Journal Archive

Johnson Matthey Technol. Rev., 2021, 65, (1), 23
doi: 10.1595/205651320X15864407040223

Professor Robert D. Gillard: Transition Metal Chemist 1936–2013: Part II

From the University of Cardiff to retirement interests and scientific legacy

  • John Burgess
  • Department of Chemistry, University of Leicester, Leicester LE1 7RH, UK
  • Martyn V. Twigg*
  • Twigg Scientific & Technical Ltd, Caxton, Cambridge CB23 3PQ, UK
  • *Correspondence may be sent via the Editorial Team: tech.review@matthey.com

Article Synopsis

The second part of this commemoration covers the final stage of Robert Gillard’s career as Professor of Inorganic Chemistry at Cardiff University and his time in retirement. At Cardiff he built on earlier work while extending his scientific interests still further into mineralogical and archaeological chemistry, and even into forensic dentistry. Coordination chemistry research continued and included the polysulfide S5 chain as a bidentate ligand in the all-inorganic cyclic PtS5 unit and the rhodium(III) complex [Rh(S5)3]3–. His penchant for discussion led him into several controversies, particularly over his ‘covalent hydration’ hypothesis of coordinated nitrogen-carbon double bonds in metal complexes which included those with platinum and 2,2’-bipyridine. He travelled widely attending international conferences and giving lectures. Research collaborations continued throughout his time at Cardiff and in particular he had many strong links with Portugal, both with colleagues there and as supervisor of Portuguese higher degree students at Cardiff. His years in retirement were spent in finalising his research legacy, in continuing to read historical literature, both chemical and otherwise, and in following his musical interests that had included many years singing in the Cwmbach Male Voice Choir.

1. Introduction

The second part of this commemoration continues the account of Professor Robert D. Gillard’s life and work from 1973 when he took up the chair of Inorganic Chemistry in Cardiff University, then a College of the University of Wales, where he stayed until his retirement. This was impelled by serious ill health in 1998, although after heart surgery he continued publishing papers for several years. At Cardiff Gillard expanded his research interests and embarked more fully into several areas. These included the hydration of coordinated nitrogen heterocycles (often referred to as “covalent hydration”) and vanadium, copper, rhodium and platinum coordination complexes – often with biologically relevant amino acids. These complexes had been given significant impetus at the University of Kent at Canterbury through funding from the Medical Research Council. At Cardiff the interests of younger members of the Department influenced additional areas of his research such as mineral chemistry (with Peter Williams) and reaction kinetics of substitution inert complexes (with Leon Kane-Maguire). All of this reflects the perpetual interest Gillard had in seeking new areas for exploration that went alongside his extensive investigations in his long standing themes of interest such as rhodium and platinum chemistry and the optical properties of chiral metal complexes. In these areas he published several multi-paper series that were interspersed with a smaller number of papers on topics that did not develop as broadly and saw publication as single papers or two-part series. Gillard had much wider scientific interests than his published work might indicate, and he was always happy to enter into vibrant enthusiastic discussion on all sorts of topics with all sorts of people, and on some occasions this would inspire him to work on topics new to him, leading to a number of joint projects. Some of these were of short duration while others involved long-term collaboration as with several Portuguese chemists.

2.1 University of Cardiff: Continued Expansion of Research Interests

The now Cardiff University was a University College of Wales when Gillard went there as Professor of Inorganic Chemistry in 1973 (he was Head of the Chemistry Department 1983–1988). It is now difficult to differentiate between research that was started there and research that was completed at Canterbury but published when he was at Cardiff. Series such as ‘Coordination Compounds and Micro-Organisms’ continued seamlessly across the change in location. However, as a Professor it is clear Gillard’s chemical interests could, and did, continue to broaden even wider.

For instance he developed a great interest in the long-known penta-atomic S5 chain as a ligand, particularly in its behaviour as a bidentate ligand in the cyclic PtS5 unit that is almost unique in being a metal-complex containing an all-inorganic ring (1, 2). The short series of papers entitled ‘Sulphides of the Platinum Group Elements’ are listed in Table S8. Gillard’s contributions included an extension to the rhodium(III) complex [Rh(S5)3]3−, and a single-crystal structure determination (3) and X-ray photoelectron spectroscopy (XPS) studies on the platinum complex (4). The binding energies, 4f7/2 for platinum(IV) or 3d5/2 for rhodium(III), are lower than most of those for the respective metals bonded to oxygen or nitrogen. His brief review of these compounds in Chemistry in Britain (5) reflects his interest in the optical properties of inorganic complexes, in the history of chemistry, and in matters musical – the article includes both mention and an illustration of Elgar’s dabbling in practical chemistry, including that of sulfides.

Towards the end of his time in Canterbury Gillard had started to work on his major investigation into the properties and reactions of nitrogen-containing heterocyclic ligands and their metal complexes. In 1973, around the time of his move to Cardiff, the first reports on this research appeared. Eventually some 50 papers (6) were published in a series entitled ‘Equilibria in Complexes of N-Heterocyclic Molecules’ – plus a few others on closely related matters. Table S9 documents the first few, some intermediate examples relating to pgms, and the last few publications (7) in this series. Parts 1 to 3 set the stage for a series whose wide range is apparent from the first few parts and is still evident in the final parts 20 years later (Table S9). The metal centres that feature most prominently are iron and ruthenium (both 2+ and 3+ oxidation states in both cases); several studies feature nickel, while complexes of platinum, iridium, cobalt, copper, silver and chromium also make occasional appearances. The majority of complexes were of 1,10-phenanthroline or 2,2′-bipyridine, sometimes with nitro or methyl substituents, but related ligands such as pyridine, 2,2′-bipyrimidine, 2,4,6-tri-(2-pyridine)-1,3,5-triazine and caerulomycin, 1, (8, 9) also appear. Two terdentate ligands occasionally replaced three equivalent bidentate ligands, for example [M(2,2′-6′,2″-terpyridine)2]n+ versus [M(2,2′-bipyridine)3]n+, for increased complex stability. Alternative routes to stabilisation (with respect to substitution) of complexes or transient intermediates involved the use of ruthenium(II) rather than iron(II) and studying [Fe(diimine)2(CN)2] in place of [Fe(diimine)3]2+ (10–12). Approaches used included the determination of equilibrium constants, the establishment of rate laws, various forms of spectroscopy (visible and infrared absorption, nuclear magnetic resonance (NMR), electron spin resonance (ESR) (13–18) and circular dichroism (CD) – one of Gillard’s long-established favourite techniques), and the occasional X-ray investigation (19–22). While the investigations reported in this series ranged over preparation, characterisation and reactions of this group of complexes, the main area of interest was in apparent anomalies in their solution chemistry and Gillard’s attempts to provide a common explanation in terms of a key role played by covalent hydration and pseudobase formation.

2.1.1 Covalent Hydration and Pseudobases

Gillard spent much time speculating about the involvement of covalent hydration and pseudobase (23) intermediates in several reactions of complexes containing appropriate ligands. His proposals, first set out (24, 25) in 1973 (26) and 1974 (27), were fully detailed in a review published in 1975 (28, 29). He was particularly concerned about the possible role of covalent hydration in solution equilibria and in the possibility of participation by pseudobases as key intermediates in nucleophilic attack at low‐spin d6 and d8 complexes. The solution equilibrium studies focused on platinum(II) complexes, the mechanistic studies on diimine complexes of iron and of ruthenium, but results both from his research and that of others on such centres as Cr(III) (30, 31), Co(II), Ni(II) and Cu(II) (32–35) also featured in his discussions.

In organic chemistry, covalently hydrated species and pseudobases are formed by addition of a nucleophile to carbon in an electron-poor heteroaromatic species or addition of water across a C=N double bond. The phenomenon of covalent hydration was first described by Adrien Albert in 1952, who reported reversible hydration-dehydration of 7-hydroxypteridine, 2, when treated successively with refluxing hydrochloric acid then boiling sodium hydroxide solution (36, 37). It has been demonstrated in many bi- and poly-aza-aromatic compounds (38–42). It is rarely observed in mono-aza monocyclic rings (43, 44), but occurs with one-ring systems such as pyrimidines. In 1967 Albert suggested that in aqueous solution 1,10-phenanthroline may be in equilibrium with a hydrate (Equation (i)) (40), while even earlier (1935) T. M. Lowry suggested (45) the formation of a covalent hydrate, 3, in cyclohexane-water solutions of nicotine. Much later, Gillard himself presented evidence for a covalent hydrate of nicotine (46). The observation of a Pfeiffer effect in the N-methylphenanthrolinium cation has also been taken as evidence for the formation of a covalent hydrate (47–50), as has the fluorescence behaviour of bipy, phen and terpy (51–53). Gillard also proposed a covalent hydrate as a key intermediate in the oxidation of pyridine to 2(1H)-pyridone – Equation (ii) – when heated in a sealed tube with zinc or cadmium salts in air or oxygen (54) or with CuSO4·5H2O (55). Later workers used a similar method – hydrothermal oxidation by copper(II) nitrate – to generate 2,2′-bipyridin-6(1H)-one and 1,10-phenanthrolin-2(1H)-one, postulating a reaction pathway through intermediates such as 4(56).

(i)

 

(ii)
 

 

 

 

 

 

 

 

 

 

 

 

Loss of a proton from a covalent hydrate – or reaction of, for example, a nitrogen heterocycle with hydroxide – gives a pseudobase. Heterocycles may also react, under suitable conditions, with other nucleophiles, such as cyanide or methoxide, Equation (iii):

(iii)

to form similar species, such as pseudocyanides (pseudobase analogues; a type of Reissert intermediate) (57–61) or Meisenheimer complexes, 5 (62–66). These pseudocyanide or Meisenheimer species are also of some relevance to the following discussion of substitution mechanisms for iron and ruthenium-diimine complexes. As with the formation of covalent hydrates, pseudobase formation from monocyclic heterocycles with just one heteroatom is very difficult. Here, as with polyheteroatomic polycycles, reaction is much easier if one of the heteroatoms is quaternised. Thus 1,10-phenanthroline does form pseudobases when suitably activated, as in, for instance, pyrazino[1,2,3,4-lmn]-1,10-phenanthrolinium dication, 6, (67). Formula 7 shows the structure suggested (68) for the pseudobase form, 6. Covalent hydration and the formation of pseudobases and pseudocyanides are all facilitated by electron-withdrawing substituents; in particular quaternization of N-heterocycles leads to an increase in susceptibility to nucleophilic attack (69).

Although generally known as ‘Meisenheimer complexes’ (62–65) such anionic σ-species generated from aromatic compounds had been observed several times pre-Meisenheimer, initially with the report in 1886 (66) of a violet colour on adding alkali to a solution of 1,3-dinitrobenzene. Meisenheimer’s key contribution was the isolation of the potassium salt of the intermediate 5a in nucleophilic aromatic substitution of ethoxide at 1,3,5-trinitro-4-methoxybenzene. Terrier documents Meisenheimer intermediates derived from azaheterocycles, including 5b, which isomerises to 5c – the latter providing a model for the reactive intermediates in the Gillard mechanism discussed in this Section of the text.

Gillard reasoned that coordination of a metal ion to an N-heterocyclic ligand should have a similar effect, leading to enhanced covalent hydration or stabilisation of pseudobases and pseudocyanides. In his brief overview of 1983 Gillard summarised his approach thus

“The novel suggestion which is at the heart of my research in this field is the following: The effect on the reactivity of N-heterocycles caused by binding to metal ions (coordination) will be similar in kind to the effects of bonding the N-heterocycles to other charge acceptors, such as alkyl or aryl groups (quaternization).” (70).

A little later (1986), in his discussion of analogies between coordination and quaternization of imines, especially N-heterocycles, he commented that “much of the work done in inorganic chemistry laboratories and institutes since the time of Werner has been coordination chemistry, often involving carbonaceous ligands”, emphasising the important role of organic chemistry in coordination chemistry (71).

Equation (iv) shows the equilibria and species for a complex in which the diimine ligand is activated by coordination to a metal ion:

(iv)

As indicated at the start of this Section, and exemplified by Gillard’s initial review article on covalent hydration and related topics (Part 3 of the series ‘Equilibria in Complexes of N-Heterocyclic Molecules’ – see Table S9), his interests in this area embraced complexes of a wide range of elements. However, there was a marked concentration on complexes of platinum(II) and of iron and ruthenium, which featured in the first and second parts of this series (Table S9). Complexes of Gillard’s much-favoured rhodium and of the much-studied cobalt(III) and chromium(III) make very few appearances, though the thermal and photochemical lability (72, 73) of [Cr(bipy)3]3+, [Cr(terpy)2]3+ and [Cr(phen)3]3+ provided an early example of the anomalies (74, 75) that prompted his covalent hydration theories, and [Cr(bipy)3]3+ is the subject of Part 47 (31), almost at the end of this series (Table S9). Cobalt(III) makes an appearance in the form of cis-[Co(en)2(benzimidazole)Cl]2+, whose relatively rapid base hydrolysis (76) is, by implication, facilitated by covalent hydration (70, 77, 78). Substitution-labile 2+ first-row transition metals also, understandably, make very few appearances, though nickel(II) does appear in Parts 10, 22, 28, 46 and 50 of this series.

The covalent hydration theory was applied to aqueous solutions of several platinum(II) complexes. Thus, for example, the oft-reported, though occasionally denied (70, 79), acidity of salts of [Pt(py)4Cl2]2+ in aqueous solution was attributed to the equilibrium shown as Equation (v):

(v)

Similarly, Gillard claimed, on the basis of 1H NMR spectra, to have identified a covalently hydrated species derived from [Pt(bipy)(CN)2]·H2O (80, 81). Gillard’s nine publications referring to nucleophilic attack at bis-diimine-platinum(II) complexes are summarised in a paper published in the year of his retirement, which detailed and compared observations on the series of bis-diazine complexes [Pt(LL)2]2+ with LL = 2,2′-bipyridine, 2,2′-bipyrazine, 3,3′-bipyridazine, and 2,2′-bipyrimidine (82). After his retirement he gathered together a number of examples of cases where he had applied his covalent hydration and pseudobase theory to platinum(II) complexes of bipy, 5,5′-Me2bipy and terpy. The evidence he deployed embraced equilibrium measurements, kinetics, electronic absorption spectra (including circular dichroism) and the relation of proposed solution species to well-known 5-coordinated platinum species. This review article, dedicated to the eminent Croatian chemist (and fellow inorganic kineticist) Smiljko Ašperger, gave an overview of solution equilibria involving hydroxide and bis-diimine-platinum(II) or terimine ([Pt(terpy)Cl]+) complexes (83).

As stated above, the main area of interest in this series was in iron and, to a somewhat smaller extent, ruthenium. The central question was the mechanism of attack by hydroxide at low-spin iron(II) complexes of N-heterocyclic ligands. The rate law for reaction of most diimine-iron(II) complexes in basic solution is as given in Equation (vi):

(vi)

Here the k2[OH−] term dominates under most conditions (84, 85). But the approach of OH− to low-spin d6 Fe(II) in an SN2 mechanism would be difficult due to the full complement of t2g electrons – as is well exemplified by base hydrolysis of cobalt(III)-amine complexes (cf. Section 3.4, Part I (86)), which proceeds by the SN1CB route. Gillard therefore proposed his mechanism involving covalent hydration and pseudobase formation (Scheme I); the key steps are detailed in Equation (vii). The hydroxide in the intermediate conjugate base both reduces the aromaticity of the ligating ring and places it in close proximity to the iron. The key papers for the kinetic and mechanistic aspects are the reviews cited above, plus Part 31 of the ‘Equilibria in Complexes of N-Heterocyclic Molecules’ series (87–89). In that part, results for [Fe(LL)3]2+ with LL = phenanthroline, bipyridyl, bipyrimidinyl, bipyrazinyl and bipyridazinyl from several earlier parts are collected and compared.

(vii)

 

Scheme I.

Gillard’s ‘covalent hydration’ mechanism for base hydrolysis of d6 transition metal complexes (M = Fe, Ru), as set out in his 1975 review (29)

There is some early spectroscopic evidence said to support the intermediacy of covalent hydration or pseudobase formation in reactions of iron(II)- and ruthenium(II)-diimine complexes. Thus, for example, electronic spectra of M(5NO2phen)32+, M = FeII, RuII and 5NO2phen = 5-nitro-1,10-phenanthroline, in basic solution were said to be consistent with pseudobase formation in basic aqueous solution (89). The 1H-NMR spectrum of K2[Fe(phen)(CN)4] dissolved in D2O shows an unexpected non-equivalence of the two halves of the ligand molecule; this inequivalence was attributed to the covalent hydrate, 8 (90–93).

Much later, extensive NMR evidence was reported for the formation (facilitated by the electron-withdrawing 5-nitro-substituent) of adducts in reactions of [Ru(5NO2phen)2(bipy)]2+ and of [Ru(5NO2phen)(bipy)2]2+ with hydroxide or cyanide in aqueous solution (94) However, such adducts, 9 and 10, like those proposed (95, 96) for 5-nitro-1,10-phenanthroline itself with hydroxide or with methoxide, 11, have the added nucleophile in a position far removed from the metal atom, indicating a different mechanism (of ligand cleavage to give a high-spin species) from that shown in Scheme I for the slow reaction of these compounds with hydroxide (96, 97).

Complexes of the [Ru(diimine)2(CN)2] type are particularly substitution-inert with respect to the metal centre and thus particularly suitable for seeking model intermediates. The complexes where the diimine is 1,10-phenanthroline, 2,2’-bipyridine, 5-nitro-1,10-phenanthroline or 5,5’-dimethyl-2,2’-bipyridine react reversibly with hydroxide or cyanide to form new species whose electronic spectra were deemed consistent with their being pseudobases or pseudocyanides (81).

The thermogravimetric behaviour of [Fe(phen)2(CN)2]·2H2O provides another, though very different, instance where the results may be interpreted in terms of covalent hydration. Whereas phen·H2O loses its water of crystallisation at 93ºC (the resultant anhydrous phen melts, without decomposition, at 117ºC), hydrated [Fe(phen)2(CN)2] does not lose its water of crystallisation until 323.5ºC, at which temperature decomposition rapidly occurs (98).

The thermogravimetric study was carried out by Hans-Ulrich Hummel, from Brodersen’s group in Erlangen (Section 2.6, Part I (86)). His visit to Cardiff gave rise to two publications related to the subject of addition to complexes of N-heterocyclic molecules. The first joint paper discussed the thermogravimetric behaviour of hydrated [Fe(phen)2(CN)2] (98). This appeared as Part 44 of the series ‘Equilibria in Complexes of N-Heterocyclic Molecules’. There seems to be some uncertainty over the hydrate(s) of [Fe(phen)2(CN)2] – Gillard and Hummel, Schilt (earlier, (12)), and a Chinese group (later, (99)) all used the same method of preparation, but whereas Schilt, on the basis of elemental analysis, and Gillard and Hummel (albeit without reporting elemental analysis results) formulated their compound as a dihydrate, the Chinese X-ray structure analysis indicates a trihydrate. Interestingly, Schilt had earlier characterised the 2,2′-bipyridine analogue as the trihydrate [Fe(bipy)2(CN)2]·3H2O (12). The second paper appeared, coincidentally also as Part 44, in the ‘Optically-Active Coordination-Compounds’ series (100), but is a complementary study of [Fe(phen)2(CN)2] involving the addition of Lewis acids, here Hg2+, Hg(CN)2, BF3, to the coordinated cyanide. In contrast to the controversial subject of the addition of nucleophiles to coordinated diimine ligands in complexes of the [M(diimine)3]2+ type, the addition of electrophilic entities such as Hg2+ to coordinated cyanide in complexes of the [M(diimine)2(CN)2] type is a long-established feature of their chemistry (see for example (101)).

Gillard’s proposals were thought contentious by many. Despite the possibilities for interpreting a variety of spectroscopic, kinetic, and thermogravimetric observations in terms of covalent hydration of diimine ligands, there appears to be no hard evidence, such as from an X-ray structural demonstration, for the existence of a stable, or even ephemeral, covalent hydrate of the type proposed by Gillard. As observed by Constable in his 2016 review cited below – “The Gillard hypothesis was remarkable in being logical and reasonable but in having very little unequivocal experimental evidence to support it.” Many of Gillard’s publications reporting experimental kinetic or spectroscopic results attracted considerable criticism from several authors, including Gwyneth Nord and Ole Mønsted (see below) and, especially, Nick Serpone in 1983 (78) who offered the most trenchant criticism. Less intemperate and more sympathetic consideration was provided by Ed Constable, both in 1983 (“The reactions of nucleophiles with complexes of chelating heterocyclic imines: A critical survey”) (102) and, more recently in 2016 (75). Gillard published a mild response (70) to Serpone’s criticism in which he presented comparisons with analogous organic reactions; he was unhappy about the concentration on platinum complexes in critical comments. The whole topic was hotly debated in sessions at the Royal Society of Chemistry Autumn Meeting (chaired by one of the present authors (MVT)) and at a meeting of the Inorganic Mechanism Discussion Group (IMDG), both held in Cardiff in 1980 (103). A facet of the pseudobase controversy published, by Gillard and Wademan, outside the ‘Equilibria in Complexes of N-Heterocyclic Molecules’ series involved the trans-[Pt(py)4Cl2]2+ cation and the possibility of a pseudobase of pyridine being involved. Their proposal (104) attracted critical comments from Seddon, Constable and Wernberg (105) (who also took issue (106) with Gillard and Hughes’s proposal (107) of a covalently hydrated form of the cis-[Ru(bipy)2(py)2]2+ in equilibrium with this complex in alkaline media) and from Mønsted and Nord (79). These criticisms were rebutted by the proposers (108), who also took issue with earlier comments by the latter authors on the relative importance of this area of pseudobase chemistry to organic and to inorganic chemistry (109). In Nord’s 1985 contribution to Comments on Inorganic Chemistry (110) she reviewed equilibrium, structural and spectroscopic (NMR) evidence as well as kinetic. She asserted that there was no unequivocal evidence (111, 112) for nucleophile (OH− or CN−)-substituted compounds or transient intermediates in this group of reactions. This article provides a useful, if admittedly biased, overview, linking the base hydrolysis mechanism of these complexes with the closely related topics of reduction of [M(LL)3]3+ (M = Fe, Ru, Os) and hydroxide attack at coordinated 1,10-phenanthroline activated by 5-nitro or 5-sulfonate substituents.

The concept of covalent hydration was also applied to some systems in the solid state (cf. (98)). Thus, for example, Gillard proposed (113) – on the basis of 1H NMR spectra of [Ir(bipy)3]3+ in d6-DMSO solution – that [Ir(bipy)3]Cl3·4H2O was the trihydrate of a complex containing one of the bipy ligands covalently hydrated. His proposal was countered by those preferring a structure containing one unidentate ligand (114–119). Gillard’s arguments in favour of covalently-hydrated intermediates rather than intermediates involving a unidentate bipy ligand were set out in his discussion of the ruthenium analogue (120). However, the controversy was resolved by the X-ray crystal structure determination (121–123) of the hydrated perchlorate salt of [Ir(bipy)3]3+, which indicated that the apparently anomalous properties of this cation were due to one of the bipy ligands being C,N-bonded to the metal, 12a and 12b, an unusual mode of attachment reminiscent of orthometalation. This is a well-known reaction in organometallic chemistry with many applications in syntheses of organic compounds.

 

 

 

 

 

 

 

In a link to his biochemical interests (124–126), Gillard suggested a covalently-hydrated form of trans-[Rh(py)4Cl2]+ in the course of a conference presentation on the effects of some rhodium complexes on bacterial growth (see Part 10 in Table S5). There have been several searches for similar intermediates in reactions of binuclear copper(II)-diimine complexes, which are related, if distantly, to the CuICuII species which figure in long-distance electron transfer in metalloproteins. Indeed, evidence has been presented for ligand-hydroxylation in two such species, of bipy and of phen (56). However, similar investigations of binuclear copper(II)-diimine (diimine = bipy or phen) (127) and copper(II)-bipy-oxalate (128) complexes, and of a cadmium-phen-chloride-acetate complex (129) failed to find any indication of OH attachment to coordinated bipy or phen.

At the time Gillard retired (1998), his ideas about the role of covalent hydration and of pseudobases were viewed with suspicion by many of the workers in this field. There was a considerable amount of spectroscopic and kinetic evidence to support his postulates, but much of it was somewhat equivocal or circumstantial, and often applied to the ligand molecules rather than to their metal complexes. There was a complete lack of a structural determination for a covalent hydrate, pseudobase or Reissert intermediate isolated from an inorganic complex reacted with water or hydroxide (130, 131). Despite the evidence from circular dichroism spectra for covalent hydration of coordinated phenanthroline in solutions containing [Ni(phen)3]I2·3H2O (35), a structure determination – by the Gillard group – failed to provide any evidence of ligand-water interaction in the solid state (20, 21, 132). In fact the water molecules occur, together with the iodide ions, in layers separating the layers of complex cations.

After Gillard’s retirement it became steadily more apparent that covalent hydration and pseudobase formation play a role in at least some redox systems involving ruthenium-diimine complexes – as adumbrated by Nord as early as 1975 (112). Thus Ledney and Dutta furnished spectroscopic evidence for intermediate addition of hydroxide to coordinated bipy in the [Ru(bipy)3]2+-catalysed oxidation of water when the catalyst is embedded in a zeolite matrix – such isolation of the complex precludes the degradation reactions which dominate in aqueous solution. These authors state specifically that “The reaction is initiated by water attack on the bipyridine ligand to form a covalent hydrate” (133). This builds on an earlier proposal by Sutin that ligand degradation in hydroxide-dependent reduction of Group 8 [M(bipy)3]3+ ions involved rate-determining attack of hydroxide on bipy-carbon to give a transient pseudobase (134, 135). A similar mechanism has been suggested for water oxidation catalysed by dimeric μ-oxo-bridged ions cis,cis-{[RuIII(bipy)2(OH2)}2O]4+ or a ring-substituted derivative (136, 137).

Density functional theory (DFT) calculations suggest that the addition of water or hydroxide to coordinated 2,2′-bipyridine may well take place in redox reactions of the ruthenium(IV) and ruthenium(V) complexes [(NH3)3(bipy)RuOH]n+ and [(NH3)3(bipy)Ru=O]n+ (n = 2 and 3) (138). The calculations indicate a strong dependence on the nature of the other coordinated ligands, with the addition of hydroxide to Ru3+-coordinated 2,2′-bipyridine seemingly very much less favourable for, for example, [Ru(bipy)3]2+ (139). Similarly, theoretical analysis of catalysis of water oxidation by [(terpy)(bpz)RuIV=O]2+ (terpy = 2,2′:6′,2′-terpyridine; bpz = 2,2′-bipyrazine) revealed a possible pathway through addition of hydroxyl to the coordinated terpy (140).

An interesting variant on the Gillard covalent hydration mechanism has been suggested based on studies of intermediates isolated from the reaction of phen with copper nitrate in weakly alkaline solution to give a binuclear product. Here it is proposed that the attacking nucleophile may be [Cu(phen)2(OH)]− rather than free OH– (141).

The opening years of the 21st century have seen a resurgence of interest in the species formed by [Pt(bipy)2]2+ in alkaline solution. Here, in contrast to the above recent intimations of the formation of covalent hydrates or pseudobases, the formation of such intermediates or products, or indeed of earlier-postulated square-pyramidal [Pt(bipy)2(OH)]+ species, now seems very unlikely. In a Gillardesque move (142) a group from Otago (New Zealand) re-investigated the much-studied [Pt(bipy)2]2+-hydroxide-water system and obtained results best interpreted in terms of a fairly stable adduct in which one bipy ligand is effectively monodentate and the hydroxide acts as a normal ligand in the square planar array around the metal, (13, with X = OH) (143). Supporting evidence for a structure of this type was subsequently provided by a study of the reactions of [Pt(bipy)2]2+ with over 20 bases, mainly pyridine derivatives (144). Further support was provided by extensions to the range of incoming ligands studied and of instrumental techniques (145), and to ternary platinum(II)-bipy-nitro complexes (146). It is a matter of some regret that these authors apparently did not examine analogous systems where the flexible 2,2′-bipyridine is replaced by the more sterically demanding 1,10-phenanthroline (119, 147).

The second decade of the 21st century has, on the other hand, seen Gillard’s work and speculations on mechanisms of nucleophilic (OH−; CN−) attack at [M(diimine)3]2+ (M = Fe; Ru) increasingly ignored or forgotten. Thus, for example, there is no mention of a Gillard-type mechanism in a recently published study of micellar effects on base hydrolysis of Fe2+ complexes of sulfonated and unsulfonated phenyl-1,2,4-triazine complexes (148, 149), while there was no consideration of covalently hydrated intermediates or similar species in the DFT treatment of 18O kinetic isotope effects on catalysis by the cis,cis-{[RuIII(bipy)2(OH2)}2O]4+ cation mentioned above (150).

To summarise the current situation regarding Gillard’s covalent hydrates and pseudobases:

  1. It is possible that they are intermediates in some of the ruthenium redox systems mentioned above

  2. Their occurrence is most unlikely in platinum-bipy-hydroxide-water systems

  3. The position in regard to hydroxide (and cyanide) attack at diimine complexes of iron(II) or ruthenium(II) is still unclear, as outlined in the next paragraph.

It is still difficult for some, as it was in 1962 (85), to accept that the k2[Fe(diimine)32+][OH−] term in the long-known rate law of Equation (vi) arises from direct attack of hydroxide on the low-spin d6 metal centre. Margerum and Morgenthaler suggested transient intermediates with incoming OH−, CN− or N3− interacting with Fe and simultaneously with a pyridine ring of the leaving ligand. This was probably the source of Nord’s suggested intermediate (See Scheme II of (151)) in the dissociative redox reaction of tris-diimine complexes of iron(III) or ruthenium(III) in basic solution, where interaction between the H of the hydroxide and ligand nitrogen of the leaving ligand – as outlined in 14– rather than the O of the hydroxide with ligand C, assists the dissociation. Such an intermediate in the base hydrolysis of the iron(II) or ruthenium(II) complexes, providing a route complementary to Gillard’s covalent hydrate route, could lower the barrier to hydroxide attack at the metal centre. Indeed the situation may well be even more complicated, with the transition state or intermediate involving interactions between water or hydroxide and both the metal ion and a ligand nitrogen and the observed kinetics may well be further complicated by hydration changes for the initial state as well as for the transition state or intermediate as the hydroxide concentration changes. Such complications are, of course, even more relevant to the k3[Fe(LL)32+][OH−]2 term in the rate law of Equation (vi) – this term is appreciable at hydroxide concentrations above a level as low as about 0.05 molar, but is important at high hydroxide concentrations.

2.1.2 More Controversies

In the mid-1980s, while continuing with his provocative work on reactions of coordinated N-heterocycles, Gillard weighed into another controversial area which had been a matter of interest and concern for almost two centuries. This concerned the ingestion and consequent effects of aluminium and its compounds. These may enter the body in several ways, intentionally or otherwise. They may be ingested in food or drink, introduced intentionally in medicines or cosmetics, or incidentally in water used for dialysis, even drinking water, or may be inhaled or absorbed by workers in mining, processing or manufacturing industries. The questions then arise as to whether the aluminium becomes involved in metabolic processes and whether it is toxic (152–157).

The possibility that the ingestion of aluminium might lead to the onset of various maladies had been raised occasionally since early in the 19th century – the likely first case of presumed aluminium poisoning was reported in 1828. Arguments over whether or not aluminium compounds were a threat to human health and well-being probably started during the subsequent law suit (See pp. 39–40 of (152)). Alum has been added to flour used in baking since the early 19th century; from about 1880 to 1920 there raged the ‘baking powder wars’ during which the relative merits and demerits (culinary and toxicity) of added alum versus added tartrate (more expensive) were hotly debated. As early as 1857 a Dr John Snow reported in The Lancet that there seemed to be a connection between the development of rickets in young children and the consumption of bread made with alum-containing flour. His article was reproduced in 2003 in the International Journal of Epidemiology, where it was followed by commentaries from A. Hardy, M. Dunnigan and N. Paneth – see pages 336–343 of Volume 32 (153–156). More recently Chesney has reconsidered the possible role of aluminium in the development of rickets (157). Questions over the absorption and subsequent effects (especially in relation to kidney function and to the onset of dementia) of aluminium in food and drink were causing widespread concern and controversy in the 1970s. Gillard made his minimal sally into the field, in 1986, through the topic of significant incorporation of aluminium into food from aluminium cookware (cf. (158), one of many papers on this subject during this period).

Gillard’s reading of this paper on the leaching of aluminium from saucepans (158) prompted him, in 1986, to write a letter to Nature entitled ‘Beware the Cups that Cheer’ (159). Gillard’s interest in this area grew out of:

  1. his work on complexes and their effects on microorganisms, such as his investigations into the bactericidal effects of various platinum group metal (pgm) complexes (Section 3.4, Part I (86) on research at Canterbury)

  2. a developing interest in the research of Margaret Farago and her group at Imperial College on the effects of added inorganic species on the growth of aquatic plants (160–162)

  3. another developing interest, into food materials, subsequently reflected in a significant review on metal-protein interactions with Stuart Laurie (163).

In this letter Gillard indicated that his interest in the possible harmful effects of ingested aluminium arose from four papers on medical aspects, an article on the mobilisation of aluminium from cookware and three publications dealing with the accumulation of aluminium by tea plants (164–167). The topics, titles and citations for these papers are set out in Table S10.

In practice his contribution to the argument, simply counselling readers to moderate their intake of tea, was miniscule, and he never returned to this subject (at least in print). Uncharacteristically, he did not even respond to the prompt and succinct comment criticising this, and other articles on beverages and foods containing only low levels of aluminium, on the grounds that pickles and baking powders often contain much higher levels of aluminium (168). In retrospect Gillard was wise to exit this area promptly, for although he expressed no further interest in this topic, concern and controversy over the possible health hazards of ingesting aluminium have continued to generate a large number of publications right up to the present day (169–175).

Gillard played a minor role in two other long-running controversies, the so-called Rupp affair and the question of the (non)existence of 1,10-phenanthroline-N,N′-dioxide. In the case of the former his role was of elucidation rather than participation (176); in the latter case he twice detailed and rebutted the first (177), and later (178–181), claims for its synthesis and the reasons for failure (182, 183). However, subsequently a successful synthesis of the N,N′-dioxide was achieved using HOF·CH3CN as oxidant. Its structure was shown to involve a novel helical geometry to minimise steric interactions between the two oxygen atoms (184). In fact Gillard was right in dismissing all the then-extant (1989) claims for having prepared 1,10-phenanthroline-N,N′-dioxide – the particularly powerful oxidant HOF·CH3CN was needed (in 1999) to overcome the aromatic resonance energy and force the phenanthroline moiety away from its heavily-favoured planarity (185, 186).

Gillard was also always keen to argue with colleagues about current controversies. Thus he was fascinated by the ‘polywater’ saga (187). There had been vague intimations of strange behaviour of water in close proximity to silica as early as the 1920s, but the controversy over ‘polywater’ (‘anomalous water’, ‘orthowater’) only started in 1966, when the eminent Russian scientist Boris V. Derjaguin presented the work of the obscure Nikolaj Fedyakin (188) at a Faraday Society Discussion at Nottingham (189) and subsequently (July, 1967) at a conference at Meriden, NH, USA. The status of polywater probably reached its zenith with the First International Conference on Polywater, sponsored by the American Chemical Society at Lehigh University in 1970. There and thereafter there were heated disputes over its nature, or indeed its very existence, until it became increasingly clear that its exceptional properties were due to its content of colloidal silica (see, for example (190)). Polywater soon moved from chemical science to pathological science (see for example (191)) to philosophy (see, for example (192, 193)). Gillard must have revelled in the arguments. Fortunately for him he did not rush into print on this subject – despite his interest in the effects of solutes on water structure in the late 1960s (cf. Table S7).

2.1.3 Oxometallates and Amino Acids

In 1982 Gillard published the first of his papers on molybdenum(VI) amino acid complexes that comprised one of his shortest series; the second and last followed in 1990. These dealt with speciation in aqueous molybdate solutions to which L = aspartate (194) or (R)-cysteine (195) had been added. The latter investigation also included analogous tungstate systems. In 1988 he began publishing a somewhat longer series, of eight parts, on oxovanadium(IV) complexes of amino acids (Table S11). Gillard and his Portuguese colleagues seemed to be particularly keen to present their results in the oxovanadium(IV) area at conferences; a number of abstracts appeared in reports on conference proceedings in the Journal of Inorganic Biochemistry between 1991 and 1997 (Table S12).

There was also a two-paper series on N-salicylidene-amino acidate complexes of oxovanadium(IV) – Part 1 dealt with their crystal and molecular structures and with their spectroscopic properties (196), while Part 2 detailed the chemistry of the N-salicylidene-glycylglycinato complex (197). This minimal series from the mid-1990s was followed, in 2004, by a paper on cysteine and penicillamine derivatives (198). It had been preceded, as early as 1970, by a paper on oxovanadium(IV) and oxovanadium(V) complexes of N-salicylidene-amino acids and their esters (199). Whereas the formation of salicylaldimine (200, 201) metal complexes is long-known (202–206) and often studied (207, 208), the corresponding ketimine ligands and their complexes are much more reluctant to form (209, 210). However, the Gillard group showed that bis-paeonolato-copper(II) (paeonol, whose formula is shown as 15 (210–212) and, in a three-dimensional representation with ligating positions indicated, in 16, is 2-hydroxy-4-methoxy-acetophenone) reacts, on gentle heating with concentrated aqueous ammonia, to give bis-paeoliminato-copper(II), [Cu{2-O−,4-OMe-C6H3-C(=NH)Me}2]. The product, which crystallises anhydrous as the trans isomer, is of interest as a square-planar copper(II) complex. In contrast, the parent bis-paeonolato complex crystallises from aqueous media mainly as a dihydrate, presumably containing an octahedral (or tetragonal) copper(II) centre (213, 214). These investigations into oxovanadium(IV) complexes of amino acid derivatives were later extended to peptide (215) and to dipeptide (216, 217) ligands.

While working with his Portuguese colleagues on oxovanadium complexes Gillard also extended his career-long interest in amino acids to forensic dentistry and to archaeology. The first project (218) involved both fields, being an investigation into the determination of aspartic acid in dental collagen to establish age at death. This approach depends on the build-up over time of D-aspartyl residues in tooth enamel. The next project was concerned with the racemisation of amino acids in bone, the isolation of the relevant microorganisms (cf. the series ‘Coordination Compounds and Micro-Organisms’; Table S5 in Part I (86)), and the detection of the enzymes involved (219). This project was quickly followed by an investigation of the mineralisation of fibres in burial environments (220) and a study of the usefulness of Fourier transform infrared (FTIR) microscopy in examining remnants of dyes in long-buried textile fibres (221).

2.1.4 Into Retirement

About a dozen papers co-authored by Gillard appeared after his retirement in 1998. Five of these were published in 2000, of which two were concerned with nicotine, three with his favourite pgm, rhodium (201, 222–225). Gillard’s last chemical publication appeared in 2004 (198). It dealt with the structure of the cysteine and penicillamine N-salicylidene-aminoacidato complexes of oxovanadium(IV) in the solid state and in solution. This publication is noteworthy both as an illustration of his many links with Portugal (nine Portuguese co-authors from five locations) and the wide range of characterisation techniques used (226).

3. Legacy and Conclusions

Although it is unclear why Gillard studied chemistry rather than the originally intended mathematics at Oxford University it was a career-defining decision for he became a prolific enthusiastic researcher whose love of practical chemistry and publishing his results was obvious to all who knew him. He was a driven man, and publishing was centrally important to him. His publications spanned a wide area of coordination chemistry that included significant contributions from that of the pgms rhodium and platinum itself, and he helped to bring this subject as a whole to the forefront of scientific awareness at a time when new types of compounds were being identified (75, 227). Fundamentally Gillard was a preparative chemist who characterised what he prepared using chemical and a variety of physical techniques then available to him.

Gillard’s formative research began at Oxford, supervised by Harry Irving. This was followed by a prolific PhD with Geoffrey Wilkinson at Imperial College, in whose laboratory he prepared a wide range of new coordination complexes especially those of rhodium and other kinetically-inert metal centres. Later he worked independently on an increasing number of topics maintaining a fast pace at Sheffield University, the University of Kent at Canterbury and finally at Cardiff University. Gillard always worked at a frenetic pace. Perhaps in some instances this led to premature conclusions being rushed into print in some of his many short publications. This state of affairs could have been modified had time been taken to complete additional work and discuss his findings more fully with colleagues.

His major scientific legacy is contained in some 400 scientific papers and review articles, of which we have been able to mention less than a quarter in the present article. He organised many of his publications – over a third – into series, as documented in Tables S1 to S9 and Table S11. Scheme II details titles, time ranges and numbers of parts, and thus gives some idea of the relation of his main areas of interest and activity to his progress through his career. Scheme III details his publishing activity during his life. Both Scheme II and Scheme III illustrate how his research career waxed and waned, and how it related to his various affiliations.

Scheme II.

Summary of Gillard’s main series of publications. The sequence of numbers for each series details the number of publications in that series for each year; the part number for the final part of each series is given in the shaded box at the end of each series block. It is interesting to follow the detailed chronological progress of individual series, some showing steady progress, others illustrating a very sporadic progress. Explanation of symbols: * A brief Erratum to Part 51 appeared the following year (1996); ♦ The untraced Parts 35 to 39 and 41 to 43 (see (6)) should have appeared in the period 1982 to 1984. a Table S1; b Table S2; c Table S3; d Table S4; e Table S5; f Table S7; g Table S6; h Table S9; i Table S8; j Table S11

Scheme III.

Gillard’s life and publications, relating annual numbers of articles published (third column, depicted diagrammatically on the right of the Scheme) to year and to the major changes in his life and career. aThe abbreviation BBH denotes Burt, Boulton and Haywood Ltd. It is interesting to note the early surge in publications in the mid-1960s and the quite rapid decrease in his publishing rate after the moderate rate of the first half of the 1990s

Another major aspect of his legacy was, and is, personified by all the research colleagues who went round the world and made significant achievements in their own right. Of more than a hundred such colleagues many became professors or gained positions of importance in academia or industry. He also influenced inorganic chemists of his generation through frequent participation in conferences and symposia, both in his presentations and in the course of discussions. In 1998 a particularly happy meeting marking his retirement was held in Cardiff, attended by many of his research colleagues and former students (Figure 1). It is a great pity that no Festschrift was published to commemorate his career in research.

Fig. 1

Robert D. Gillard with his long time Australian friend Professor Brice Bosnich (left) at Gillard’s retirement event held in Cardiff in 1998 (Courtesy of Professor A. W. Addison)

The chemical highlights of his research career included the synthesis of a totally inorganic optically active platinum polysulfide which is a significant example of a chiral compound with no carbon centre. Expanding further the coordination chemistry of cobalt(III) complexes pioneered by Alfred Werner (228, 229), especially their optically active properties, was central in Gillard’s career. Starting at Imperial College he worked tirelessly on the chemistry of new rhodium(III) complexes and on correcting the formulation of long-known ones.

One of Gillard’s great personal fascinations was to read the older chemical literature, like the early work of Delépine and Poulenc on rhodium chemistry and old transition metal cyanide chemistry. His extremely well used (former British Library book) copy of the second edition (1948) of “Cyanogen Compounds” by H. E. Williams (230, 231) was littered with inserted scraps of paper noting particularly intriguing observations. Such information inspired him to do experiments and, with modern techniques, extend understanding in these areas (233, 232). Complementing (and overshadowing) this interest in the past, Gillard’s interests constantly developed and diversified throughout his career. As late as 1994, only a little time before he completely retired, he published the results of work in another area new to him which might be called archeological chemistry (outlined at the end of Section 2.1.3)! This illustrates the sense of enjoyment Gillard got from the entire research process from first idea, doing experiments, coming to conclusions and publishing the results.

He worked very hard and was successful in several areas outside his chemical career. His musical abilities have been highlighted in Part I (86) and he was something of a linguist speaking Portuguese as well as some German, Italian, French, Welsh and even able to converse in Hungarian and some Dutch. It is said that in retirement he became interested in the Victorian and Edwardian eras, writing a biography of the Portuguese diplomat the Marquis de Soveral, Envoy Extraordinaire to the Court of St James, and completing a first draft of an account of the popularity of tattoos among the Victorian aristocracy. His daughters aptly characterised him as “a Renaissance chemist” (234, 235). Gillard was always very personable and he exuded a fun for and an enjoyment of life that was infectious to all who met him (Figure 2). It is not surprising that he had a huge number of colleagues around the world (his daughters’ obituary lists 16 countries with which he had chemical contacts) who thought of him as a good friend. Gillard’s passing was a shock to his family and everyone who knew him, and he is deeply missed by all.

Fig. 2

One of the last photographs of Robert D. Gillard, having lunch with old friends in Cardiff in 2012 (Courtesy Dr J. G. Jones)

References and Notes

  1. 1.
    The inorganic/organic borderline species tris-carbonatocobalt(III) provides a link to Gillard’s series “Optically-Active Coordination Compounds” – Part 28 of which reports the resolution of this complex by the use of (+)[Co(en) 3] 3+ (2)
  2. 2.
    R. D. Gillard, P. R. Mitchell and M. G. Price, J. Chem. Soc., Dalton Trans., 1972, (12), 1211–1213 LINK https://doi.org/10.1039/DT9720001211
  3. 3.
    P. Cartwright, R. D. Gillard, R. Sillanpaa and J. Valkonen, Polyhedron, 1987, 6, (9), 1775–1779 LINK https://doi.org/10.1016/S0277-5387(00)86549-3
  4. 4.
    A. N. Buckley, H. J. Wouterlood, P. S. Cartwright and R. D. Gillard, Inorg. Chim. Acta, 1988, 143, (1), 77–80 LINK https://doi.org/10.1016/S0020-1693(00)85848-X
  5. 5.
    R. D. Gillard, Chem. Brit., 1984, 20, (11), 1022–1024
  6. 6.
    It is impossible to give a reliable estimate for the number of publications in this Series as several part numbers appear to be missing. The existence of two Part 17s and two Part 50s complicates the situation, while the fact that P. A. Williams is the sole author of Part 23 adds a further complication
  7. 7.
    The final paper is dated 2001, three years after he retired and 28 years after Part 1 was published
  8. 8.
    In Part 34 caerulomycin, which contains a bipy moiety, provides an exotic example of an N-heterocyclic ligand – see (9) – and a link to the “Coordination Compounds and Micro-Organisms” series
  9. 9.
    S. Dholakia and R. D. Gillard, J. Chem. Soc., Dalton Trans., 1984, (10), 2245–2248 LINK https://doi.org/10.1039/DT9840002245
  10. 10.
    Fe(bipy) 2(CN) 2 and Fe(phen) 2(CN) 2 are so-called Schilt-Barbieri compounds (11, 12)
  11. 11.
    G. A. Barbieri, Atti Accad. Lincei, 1934, 20, 273–278
  12. 12.
    A. A. Schilt, J. Am. Chem. Soc., 1960, 82, (12), 3000–3005 LINK https://doi.org/10.1021/ja01497a007
  13. 13.
    Though ESR was rarely used in the studies reported in this Series, Gillard used this technique extensively in later work on oxovanadium(IV) complexes (see, for example, Parts 7 and 8 of the series “Oxovanadium(IV) – Amino-Acids” – Table S11 – and (14). ESR also featured in his work on silver(II) (15) and in a few of his rhodium studies. These latter included investigation of Rh(II) species in zeolite catalysts (16) and of the paramagnetic dioxygen complexes of rhodium cis- and trans-[Rh(O 2)(en) 2Cl] +, [[Rh(en) 2Cl] 2(μ-O 2)] 3+ and [(RhL 4Cl) 2 (μ-O 2)] 3+ (L = 4-methylpyridine). Here ESR showed that the complexes contain the Rh(III)-O 2 − moiety with the unpaired electron localised on the O 2 (17). Despite his extensive work on copper, he seems very rarely to have obtained ESR spectra of copper complexes. However, his study of equilibria at high pH in copper(II)/amino-acid solutions (18) does provide one instance
  14. 14.
    J. Costa Pessoa, L. F. Vilas Boas and R. D. Gillard, Polyhedron, 1989, 8, (13–14), 1745–1747 LINK https://doi.org/10.1016/S0277-5387(00)80628-2
  15. 15.
    J. C. Evans, R. D. Gillard, R. J. Lancashire and P. H. Morgan, J. Chem. Soc . Dalton Trans., 1980, (8), 1277–1281 LINK https://doi.org/10.1039/DT9800001277
  16. 16.
    I. J. Ellison, R. D. Gillard and J. P. Maher, Trans. Met. Chem., 2000, 25, (6), 626–627 LINK https://doi.org/10.1023/A:1007037309165
  17. 17.
    J. B. Raynor, R. D. Gillard and J. D. Pedrosa de Jesus, J. Chem. Soc., Dalton Trans., 1982, (6), 1165–1166 LINK https://doi.org/10.1039/DT9820001165
  18. 18.
    R. D. Gillard, R. J. Lancashire and P. O’Brien, Trans. Met. Chem., 1980, 5, (1), 340–345 LINK https://doi.org/10.1007/BF01396956
  19. 19.
    X-Ray powder patterns were used, alongside colour and hydration data, to characterise various tris-(1,10-phenanthroline)nickel(II) salt hydrates (20), and X-ray structure determinations carried out on the iodide trihydrate of this complex (21) and on the dimorphs of fac-[Ir(py) 3Cl 3] (22)
  20. 20.
    R. D. Gillard and S. H. Mitchell, Polyhedron, 1988, 7, (13), 1175–1186 LINK https://doi.org/10.1016/S0277-5387(00)81206-1
  21. 21.
    R. D. Gillard, S. H. Mitchell and W. T. Robinson, Polyhedron, 1989, 8, (22), 2649–2655 LINK https://doi.org/10.1016/S0277-5387(00)80435-0
  22. 22.
    R. D. Gillard and S. H. Mitchell, Polyhedron, 1989, 8, (18), 2245–2249 LINK https://doi.org/10.1016/S0277-5387(00)81250-4
  23. 23.
    Covalent hydration involves the addition of water across a ring carbon-nitrogen bond in a heterocyclic compound, a pseudobase is generated by addition of an anion (e.g. hydroxide) to a ring carbon atom in a (generally quaternised) nitrogen heterocycle – either way producing a four-coordinate carbon bearing an activated nucleophile
  24. 24.
    However Gillard had earlier hinted at the possibility of the occurrence of covalent hydration, for example in his 1969 paper with Brian Heaton on the properties of complexes [M(LL) 2X 2] + (M = Rh or Ir, LL = bipy or phen, X = Cl or Br – see (25)
  25. 25.
    R. D. Gillard and B. T. Heaton, J. Chem. Soc. A, 1969, 451–454 LINK https://doi.org/10.1039/J19690000451
  26. 26.
    R. D. Gillard and J. R. Lyons, J. Chem. Soc., Chem. Commun., 1973, (16), 585–586 LINK https://doi.org/10.1039/C39730000585
  27. 27.
    R. D. Gillard, Inorg. Chim. Acta, 1974, 11, L21–L22 LINK https://doi.org/10.1016/S0020-1693(00)93676-4
  28. 28.
    “Equilibria in Complexes of N-Heterocyclic Molecules. Part III. An Explanation For Classical Anomalies Among Complexes of 1,10-Phenanthrolines and 2,2′-Bipyridyls”: A lecture delivered at the Bressanone Conference on “Stability and Reactivity of Coordination Compounds”, in August, 1974, and based on lectures at Canterbury (1967), Coleraine (1974), Cambridge (1974) and Gregynog (1974) (29)
  29. 29.
    R. D. Gillard, Coord. Chem. Rev., 1975, 16, (1–2), 67–94 LINK https://doi.org/10.1016/S0010-8545(00)80285-4
  30. 30.
    The pH-rate profile of solvolysis, racemisation and photoracemisation of [Cr(bipy) 3] 3+ and the pH dependence of its luminescence behaviour suggest the intermediacy of a cation-hydroxide adduct – see (31) and references therein
  31. 31.
    P. S. Cartwright and R. D. Gillard, Polyhedron, 1989, 8, (11), 1453–1455 LINK https://doi.org/10.1016/S0277-5387(00)86261-0
  32. 32.
    Diimine complexes of cobalt(II), nickel(II) and copper(II) feature in Parts 22 (33) and 28 (34); the pH-dependent racemisation of [Ni(phen) 3] 2+ – cf. [Cr(bipy) 3] 3+ in (30) – is discussed in Part 10 (35)
  33. 33.
    R. D. Gillard and P. A. Williams, Trans. Met. Chem., 1979, 4, (1), 18–23 LINK https://doi.org/10.1007/BF00941010
  34. 34.
    J. A. Arce Sagüés, R. D. Gillard and P. A. Williams, Inorg. Chim. Acta, 1979, 36, L411–L412 LINK https://doi.org/10.1016/S0020-1693(00)89349-4
  35. 35.
    R. D. Gillard and P. A. Williams, Trans. Met. Chem., 1977, 2, (1), 14–18 LINK https://doi.org/10.1007/BF01402669
  36. 36.
    Pteridines undergo nucleophilic addition reactions, such as covalent hydration, particularly easily (37)
  37. 37.
    A. Albert, D. J. Brown and G. Cheeseman, J. Chem. Soc., 1952, 1620–1630 LINK https://doi.org/10.1039/JR9520001620
  38. 38.
    A. Albert, Adv. Heterocyclic Chem., 1976, 20, 117–143 LINK https://doi.org/10.1016/S0065-2725(08)60853-3
  39. 39.
    A. Albert, Angew. Chem., 1967, 79, (21), 913–922 LINK https://doi.org/10.1002/ange.19670792102
  40. 40.
    A. Albert, Angew. Chem., Int. Ed., 1967, 6, (11), 919–928 LINK https://doi.org/10.1002/anie.196709191
  41. 41.
    A. Albert and W. L. Armarego, Adv. Heterocycl. Chem., 1965, 4, 1–42 LINK https://doi.org/10.1016/s0065-2725(08)60873-9
  42. 42.
    D. D. Perrin, Adv. Heterocycl. Chem., 1965, 4, 43–73 LINK https://doi.org/10.1016/S0065-2725(08)60874-0
  43. 43.
    Pyridine has long been known to associate strongly with water, e.g. in ternary pyridine/water/organic cosolvent media (44), but seems unwilling to form a covalent bond
  44. 44.
    J. R. Johnson, P. J. Kilpatrick, S. D. Christian and H. E. Affsprung, J. Phys. Chem., 1968, 72, (9), 3223–3229 LINK https://doi.org/10.1021/j100855a023
  45. 45.
    T. M. Lowry, “Optical Rotatory Power”, Longmans, Green and Co, London, UK, 1935, pp. 329–333
  46. 46.
    N. S. A. Davies and R. D. Gillard, Trans. Met. Chem., 2000, 25, (6), 628–629 LINK https://doi.org/10.1023/A:1007092216627
  47. 47.
    (48); Gillard was the (co)author of two reviews on the Pfeiffer effect (49, 50) – the former from a conference held at University of Sussex
  48. 48.
    R. D. Gillard, K. W. Johns and P. A. Williams, J. Chem. Soc., Chem. Commun., 1979, (8), 357–358 LINK https://doi.org/10.1039/C39790000353
  49. 49.
    R. D. Gillard, ‘The Origin of the Pfeiffer Effect’, Proceedings of the NATO Advanced Study Institute, University of Sussex, UK, 10th–22nd September, 1978, “Optical Activity and Chiral Discrimination”, Series C – Mathematical and Physical Sciences, ed. S. F. Mason, Vol. 48, Springer Science and Business Media, Dordrecht, Holland, 1979, pp. 353–367 LINK https://doi.org/10.1007/978-94-015-7644-4_15
  50. 50.
    R. D. Gillard and P. A. Williams, Int. Rev. Phys. Chem., 1986, 5, (2–3), 301–305 LINK https://doi.org/10.1080/01442358609353395
  51. 51.
    M. S. Henry and M. Z. Hoffman, J. Am. Chem. Soc., 1977, 99, (15), 5201–5203 LINK https://doi.org/10.1021/ja00457a062
  52. 52.
    M. S. Henry and M. Z. Hoffman, J. Phys. Chem., 1979, 83, (5), 618–625 LINK https://doi.org/10.1021/j100468a012
  53. 53.
    A. Sarkar and S. Chakravorti, J. Luminescence, 1995, 63, (3), 143–148 LINK https://doi.org/10.1016/0022-2313(94)00049-I
  54. 54.
    R. D. Gillard and D. P. J. Hall, J. Chem. Soc., Chem. Commun., 1988, (17), 1163–1164 LINK https://doi.org/10.1039/C39880001163
  55. 55.
    P. Tomasik and A. Woszczyk, J. Heterocyclic Chem., 1979, 16, (6), 1283–1286 LINK https://doi.org/10.1002/jhet.5570160639
  56. 56.
    X.-M. Zhang, M.-L. Tong and X.-M. Chen, Angew. Chem., Int. Ed., 2002, 41, (6), 1029–1031 LINK  https://doi.org/10.1002/1521-3773(20020315)41:6<1029::AID-ANIE1029>3.0.CO;2-B  
  57. 57.
    A. Reissert, Ber. Deutsch. Chem. Ges., 1905, 38, (2), 1603–1614 LINK https://doi.org/10.1002/cber.19050380260
  58. 58.
    A. Reissert, Ber. Deutsch. Chem. Ges., 1905, 38, 3415–3435 LINK https://doi.org/10.1002/cber.190503803170
  59. 59.
    W. E. McEwen and R. L. Cobb, Chem. Rev., 1955, 55, (3), 511–549 LINK https://doi.org/10.1021/cr50003a002
  60. 60.
    F. D. Popp, ‘Reissert Compounds’, in “Advances in Heterocyclic Chemistry”, eds. A. R. Katritzky and A. J. Boulton, Academic Press, Cambridge, USA, Vol. 9, 1968, pp. 1–25 LINK https://doi.org/10.1016/S0065-2725(08)60370-0
  61. 61.
    F. D. Popp, ‘Developments in the Chemistry of Reissert Compounds (1968-1978)’, in “Advances in Heterocyclic Chemistry”, eds. A. R. Katritzky and A. J. Boulton, Elsevier Inc, Amsterdam, The Netherlands, Vol. 24, 1979, pp. 187–214 LINK https://doi.org/10.1016/S0065-2725(08)60511-5
  62. 62.
    J. Meisenheimer, Justus Liebigs Ann. Chem., 1902, 323, (2), 205–246 LINK https://doi.org/10.1002/jlac.19023230205
  63. 63.
    C. F. Bernasconi, Accts. Chem. Res., 1978, 11, (4), 147–152 LINK https://doi.org/10.1021/ar50124a004
  64. 64.
    F. Terrier, Chem. Rev., 1982, 82, (2), 77–152 LINK https://doi.org/10.1021/cr00048a001
  65. 65.
    G. A. Artamkina, M. P. Egorov and I. P. Beletskaya, Chem. Rev., 1982, 82, (4), 427–459 LINK https://doi.org/10.1021/cr00050a004
  66. 66.
    J. V. Janovsky and L. Erb, Ber. Deutsch. Chem. Ges., 1886, 19, (2), 2155–2158 LINK https://doi.org/10.1002/cber.188601902113
  67. 67.
    J. W. Bunting and W. G. Meathrel, Can. J. Chem., 1974, 52, (6), 975–980 LINK https://doi.org/10.1139/v74-156
  68. 68.
    A. L. Black and L. A. Summers, Tetrahedron, 1968, 24, (21), 6453–6457 LINK https://doi.org/10.1016/S0040-4020(01)96836-X
  69. 69.
    J. W. Bunting, Adv. Heterocycl. Chem., 1980, 25, 1–82 LINK https://doi.org/10.1016/S0065-2725(08)60689-3
  70. 70.
    R. D. Gillard, Coord. Chem. Rev., 1983, 50, (3), 303–309 LINK https://doi.org/10.1016/0010-8545(83)80022-8
  71. 71.
    R. D. Gillard, Comm. Inorg. Chem., 1986, 5, (4), 175–199 LINK https://doi.org/10.1080/02603598608072283
  72. 72.
    N. Serpone and M. Z. Hoffman, J. Chem. Educ., 1983, 60, (1), 853–860 LINK https://doi.org/10.1021/ed060p853
  73. 73.
    M. A. Jamieson, N. Serpone and M. Z. Hoffman, Coord. Chem. Rev., 1981, 39, (1–2), 121–179 LINK https://doi.org/10.1016/S0010-8545(00)80513-5
  74. 74.
    It should be added that references 98 to 101 of Constable’s recent review (see page 298 of (75)) argue that covalent hydration plays no role in reactions of this type
  75. 75.
    E. C. Constable, Polyhedron, 2016, 103, (Part B), 295–306 LINK https://doi.org/10.1016/j.poly.2015.03.016
  76. 76.
    D. A. House, P. R. Norman and R. W. Hay, Inorg. Chim. Acta, 1980, 45, L117–L119 LINK https://doi.org/10.1016/S0020-1693(00)80117-6
  77. 77.
    This hint appears in his riposte (70) to Serpone’s criticism (78). It is also possible that steric effects are significant, while both here and in the equilibria shown in Equation (iv) back-donation of electrons from the metal may also play a role
  78. 78.
    N. Serpone, G. Ponterini, M. A. Jamieson, F. Bolletta and M. Maestri, Coord. Chem. Rev., 1983, 50, (3), 209–302
  79. 79.
    O. Mønsted and G. Nord, J. Chem. Soc., Dalton Trans., 1981, (12), 2599 LINK https://doi.org/10.1039/DT9810002599
  80. 80.
    This observation is a byproduct of the study of reactions of complexes [M(LL) 3] 2+ . M = Fe or Ru. LL = bipy or phen, with cyanide mentioned later in the text – see (81)
  81. 81.
    R. D. Gillard, L. A. P. Kane-Maguire and P. A. Williams, Transition Met. Chem., 1976, 1, (6), 247
  82. 82.
    A. Sengül and R. D. Gillard, Trans. Met. Chem., 1998, 23, (6), 663–666 LINK https://doi.org/10.1023/A:1006936408391
  83. 83.
    A. M. F. Gameiro, R. D. Gillard, N. H. Rees, J. Schulte and A. Sengül, Croatica Chem. Acta, 2001, 74, (3), 641–665 LINK https://hrcak.srce.hr/131884
  84. 84.
    D. W. Margerum, J. Am. Chem. Soc., 1957, 79, (11), 2728–2733 LINK https://doi.org/10.1021/ja01568a017
  85. 85.
    D. W. Margerum and L. P. Morgenthaler, J. Am. Chem. Soc., 1962, 84, (5), 706–709 LINK https://doi.org/10.1021/ja00864a003
  86. 86.
    J. Burgess and M. V. Twigg, Johnson Matthey Technol. Rev., 2021, 65, (1), 4–22 LINK https://www.technology.matthey.com/article/65/1/4-22/
  87. 87.
    (88). Some early spectroscopic evidence for pseudobase formation from M(5NO 2phen) 3 2+, M = Fe(II), Ru(II) and 5NO 2 phen = 5-nitro-1,10-phenanthroline, appeared in a non-Series communication (89); the electron-withdrawing 5-nitro-substituent promotes reaction with nucleophilic hydroxide
  88. 88.
    R. D. Gillard, D. W. Knight and P. A. Williams, Trans. Met. Chem., 1980, 5, (1), 321–324 LINK https://doi.org/10.1007/BF01396950
  89. 89.
    R. D. Gillard, C. T. Hughes and P. A. Williams, Trans. Met. Chem., 1976, 1, (2), 51–52 LINK https://doi.org/10.1007/BF01385939
  90. 90.
    (91). It should be noted that NMR spectra of Fe(bipy) 2 (CN) 2 (92) and of Ru(bipy) 2 (CN) 2 (93) have been interpreted in terms of the effects of shielding by the CN group rather than in terms of covalent hydration
  91. 91.
    R. D. Gillard, C. T. Hughes, L. A. P. Kane-Maguire and P. A. Williams, Trans. Met. Chem., 1976, 1, (3), 114–118
  92. 92.
    B. V. Agarwala, K. V. Ramanathan and C. L. Khetrapal, J. Coord. Chem., 1985, 14, (2), 133–137 LINK https://doi.org/10.1080/00958978508073899
  93. 93.
    M. Maruyama, H. Matsuzawa and Y. Kaizu, Inorg. Chim. Acta, 1995, 237, (1–2), 159–162 LINK https://doi.org/10.1016/0020-1693(95)90816-O
  94. 94.
    J. A. Arce Sagüés, R. D. Gillard and P. A. Williams, Trans. Met. Chem., 1989, 14, (2), 110–114 LINK https://doi.org/10.1007/BF01040602
  95. 95.
    D. W. W. Anderson, P. Roberts, M. V. Twigg and M. B. Williams, Inorg. Chim. Acta, 1979, 34, L281–L283 LINK https://doi.org/10.1016/S0020-1693(00)94660-7
  96. 96.
    R. D. Gillard, R. P. Houghton and J. N. Tucker, J. Chem. Soc., Dalton Trans., 1980, (11), 2102–2017 LINK https://doi.org/10.1039/DT9800002102
  97. 97.
    R. D. Gillard and R. E. E. Hill, J. Chem. Soc., Dalton Trans., 1974, (11), 1217–1236 LINK https://doi.org/10.1039/DT9740001217
  98. 98.
    R. D. Gillard and H.-U. Hummel, Trans. Met. Chem., 1985, 10, (9), 348–349 LINK https://doi.org/10.1007/BF01036399
  99. 99.
    S. -Zhan, Q. -Meng, X. -You, G. Wang and P.-J. Zheng, Polyhedron, 1996, 15, (15), 2655–2658 LINK https://doi.org/10.1016/0277-5387(95)00540-4
  100. 100.
    R. D. Gillard and H. U. Hummel, J. Coord. Chem., 1986, 14, (4), 315–319 LINK https://doi.org/10.1080/00958978608075849
  101. 101.
    M. T. Beck and E. C. Porszolt, J. Coord. Chem., 1971, 1, (1), 57–66 LINK https://doi.org/10.1080/00958977108070744
  102. 102.
    E. C. Constable, Polyhedron, 1983, 2, (7), 551–572 LINK https://doi.org/10.1016/S0277-5387(00)81511-9
  103. 103.
    The session at the Autumn Meeting was part of a joint Dalton and Perkin (i.e. inorganic and organic) symposium on “Reactions of Coordinated Ligands”, which included an oral contribution by E. C. Constable and K. R. Seddon entitled “Reactivity of Coordinated 2,2′-Bipyridine and 1,10-Phenanthroline”. Nord and Gillard both made oral presentations at the IMDG meeting
  104. 104.
    R. D. Gillard and R. J. Wademan, J. Chem. Soc., Chem. Commun., 1981, (10), 448–449 LINK https://doi.org/10.1039/C39810000448
  105. 105.
    K. R. Seddon, J. E. Turp, E. C. Constable and O. Wernberg, J. Chem. Soc., Dalton Trans., 1987, (2), 293–296 LINK https://doi.org/10.1039/DT9870000293
  106. 106.
    P. B. Hitchcock, K. R. Seddon, J. E. Turp, Y. Z. Yousif, J. A. Zora, E. C. Constable and O. Wernberg, J. Chem. Soc., Dalton Trans., 1988, (7), 1837–1842 LINK https://doi.org/10.1039/DT9880001837
  107. 107.
    R. D. Gillard and C. T. Hughes, J. Chem. Soc., Chem. Commun., 1977, (21), 776–777 LINK https://doi.org/10.1039/C39770000776
  108. 108.
    R. D. Gillard and R. J. Wademan, J. Chem. Soc., Dalton Trans., 1981, (12), 2599–2600 LINK https://doi.org/10.1039/DT9810002599
  109. 109.
    O. Farver, O. Mønsted and G. Nord, J. Am. Chem. Soc., 1979, 101, (20), 6118–6120 LINK https://doi.org/10.1021/ja00514a044
  110. 110.
    G. Nord, Comm. Inorg. Chem., 1985, 4, (4), 193–211 LINK https://doi.org/10.1080/02603598508072261
  111. 111.
    Though earlier Nord had suggested the intermediacy of a pseudobase “…highly reactive precursor complex…[M(LL) 2 (R’-OH)] 2+ where R’-OH is probably the pseudo-base…”, in her discussion of the kinetics of reduction of tris(2,2’-bipyridine) and tris(1,10-phenanthroline) complexes of iron(III) and osmium(III) by hydroxide ion (112)
  112. 112.
    G. Nord and O. Wernberg, J. Chem. Soc., Dalton Trans., 1975, (10), 845–849 LINK https://doi.org/10.1039/DT9750000845
  113. 113.
    R. D. Gillard, R. J. Lancashire and P. A. Williams, J. Chem. Soc., Dalton Trans., 1979, (1), 190–192
  114. 114.
    (115). Other examples of tris-bipy complexes of iridium(III) containing a monodentate bipy plus water or hydroxide to complete the octahedral environment of the metal include (116–118). Monodentate phen bonded to platinum(II) has been demonstrated in [PtCl(PEt 3) 2 (phen)]BF 4, see (119)
  115. 115.
    R. J. Watts, J. S. Harrington and J. Van Houten, J. Am. Chem. Soc., 1977, 99, (7), 2179–2187 LINK https://doi.org/10.1021/ja00449a026
  116. 116.
    J. L. Kahl, K. W. Hanck and K. DeArmond, J. Phys. Chem., 1978, 82, (5), 540–545 LINK https://doi.org/10.1021/j100494a009
  117. 117.
    R. J. Watts and S. F. Bergeron, J. Phys. Chem., 1979, 83, (3), 424–425 LINK https://doi.org/10.1021/j100466a025
  118. 118.
    S. F. Bergeron and R. J. Watts, J. Am. Chem. Soc., 1979, 101, (12), 3151–3156 LINK https://doi.org/10.1021/ja00506a002
  119. 119.
    K. R. Dixon, Inorg. Chem., 1977, 16, (10), 2618–2624 LINK https://doi.org/10.1021/ic50176a039
  120. 120.
    J. A. A. Sagüés, R. J. Lancashire and P. A. Williams, J. Chem. Soc., Dalton Trans., 1979, (1), 193–198 LINK https://doi.org/10.1039/DT9790000193
  121. 121.
    (122). Three years later the waters of crystallisation in the analogous perchlorate salt [Ir(bipy) 3](ClO 4) 3·2⅓H 2 O were shown to be close to 5,5′ positions of the ligands; no oxygen atoms were found close to the 3(3′) positions as proposed in Gillard’s covalent hydration structure (123)
  122. 122.
    W. A. Wickramasinghe, P. H. Bird and N. Serpone, J. Chem. Soc., Chem. Commun., 1981, (24), 1284–1286 LINK https://doi.org/10.1039/C39810001284
  123. 123.
    A. C. Hazell and R. G. Hazell, Acta Cryst., 1984, C40, (5), 806–811 LINK https://doi.org/10.1107/S0108270184005801
  124. 124.
    There is also a link to his interest in mineral materials, in that he invoked covalent hydration to explain aspects of the behaviour of 1,10-phenanthroline complexes of iron(II) and of copper(II) on clay (hectorite, the smectite Na 0.3(Mg,Li) 3Si 4O 10(OH) 2) surfaces (125). A few years later Krenske et al. (126) suggested that the dependence of absorption spectra and luminescence yields on water content for [Ru(bipy) 3] 2+ absorbed on smectite membranes could be rationalised in terms of covalent hydration – quoting several Gillard references (though not the Clays and Clay Minerals (125) paper!) in support
  125. 125.
    R. D. Gillard and P. A. Williams, Clays Clay Miner., 1978, 26, 178–179 LINK https://doi.org/10.1346/CCMN.1978.0260216
  126. 126.
    D. Krenske, S. Abdo, H. Van Damme, M. Cruz and J. J. Fripiat, J. Phys. Chem., 1980, 84, (19), 2447–2457 LINK https://doi.org/10.1021/j100456a021
  127. 127.
    J.-P. Zhang, Y.-Y. Lin, Y.-Q. Weng and X.-M. Chen, Inorg. Chim. Acta, 2006, 359, (11), 3666–3670 LINK https://doi.org/10.1016/j.ica.2006.01.025
  128. 128.
    Q. Huang, L.-H. Diao and X.-H. Yin, Z. Kristallogr. NCS, 2010, 225, (4), 781–782 LINK https://doi.org/10.1524/ncrs.2010.0343
  129. 129.
    S.-F. Wu, J.-Z. Liu, M.-X. Meng and W.-Q. Luo, Z. Kristallogr. NCS, 2012, 227, (2), 163–164 LINK https://doi.org/10.1524/ncrs.2012.0073
  130. 130.
    Though it must be said that Bunting cites Gillard in this connection in his 1980 review (131)
  131. 131.
    J. W. Bunting, Adv. Heterocycl. Chem., 1980, 25, 1–82 LINK https://doi.org/10.1016/S0065-2725(08)60689-3
  132. 132.
    (21). The authors comment (their italics) “Covalent hydration was proposed for this system in solution… such modification of the ligated 1,10-phenanthroline is not present in this particular solid ”. It should be added that, in view of the extensive polymorphism – at least seven other forms – known for [Ni(phen) 3]I 2· nH 2O (20) the occurrence of covalent hydration in [Ni(phen) 3] 2+ -water systems cannot be totally ruled out
  133. 133.
    M. Ledney and P. K. Dutta, J. Am. Chem. Soc., 1995, 117, (29), 7687–7695 LINK https://doi.org/10.1021/ja00134a013
  134. 134.
    P. K. Ghosh, B. S. Brunschwig, M. Chou, C. Creutz and N. Sutin, J. Am. Chem. Soc., 1984, 106, (17), 4772–4783 LINK https://doi.org/10.1021/ja00329a022
  135. 135.
    J. K. Hurst, Coord. Chem. Rev., 2005, 249, (3–4), 313–328 LINK https://doi.org/10.1016/j.ccr.2004.06.017
  136. 136.
    H. Yamada, W. F. Siems, T. Koike and J. K. Hurst, J. Am. Chem. Soc., 2004, 126, (31), 9786–9795 LINK https://doi.org/10.1021/ja030594g
  137. 137.
    J. L. Cape, W. F. Siems and J. K. Hurst, Inorg. Chem., 2009, 48, 8729–8735 LINK https://doi.org/10.1021/ic900826q
  138. 138.
    These entities were chosen as models for intermediates in the catalysis of water oxidation by cis,cis {[Ru III(bipy) 2(OH 2)} 2O] 4+
  139. 139.
    A. Ozkanlar, J. L. Cape, J. K. Hurst and A. E. Clark, Inorg. Chem., 2011, 50, (17), 8177–8187 LINK https://doi.org/10.1021/ic200646h
  140. 140.
    L.-P. Wang, Q. Wu and T. Van Voorhis, Inorg. Chem., 2010, 49, (10), 4543–4553 LINK https://doi.org/10.1021/ic100075k
  141. 141.
    K. B. Szpakolski, K. Latham, C. J. Rix, J. M. White, B. Moubaraki and K. S. Murray, Chem. Eur. J., 2010, 16, (5), 1691–1696 LINK https://doi.org/10.1002/chem.200901720
  142. 142.
    The words we have italicised in the title “The nature of the [Pt(bipy) 2] 2+ ion in aqueous alkaline solution: a new look at an old problem ” irresistibly recall Gillard’s re-examinations of such entities as Rhodium Blue and Tipper’s Compound
  143. 143.
    C. S. McInnes, B. R. Clare, W. R. Redmond, C. R. Clark and A. G. Blackman, Dalton Trans., 2003, (11), 2215–2218 LINK https://doi.org/10.1039/B302854B
  144. 144.
    Y. Kawanishi, T. Funaki, T. Yatabe, Y. Suzuki, S. Miyamoto, Y. Shimoi and S. Abe, Inorg. Chem., 2008, 47, (9), 3477–3479 LINK https://doi.org/10.1021/ic702449k
  145. 145.
    G. Cavigliasso, R. Stranger, W. K. C. Lo, J. D. Crowley and A. G. Blackman, Polyhedron, 2013, 64, 238–246 LINK https://doi.org/10.1016/j.poly.2013.05.004
  146. 146.
    W. K. C. Lo, R. J. Shepherd, R. Stranger, A. G. Blackman and G. Cavigliasso, Polyhedron, 2017, 130, 145–153 LINK https://doi.org/10.1016/j.poly.2017.04.007
  147. 147.
    However, monodentate phen bound to platinum(II) is not unknown – as in, for instance, [PtCl(PEt 3) 2(phen)]BF 4 (see (118))
  148. 148.
    See (149) and five earlier references (from 2012 to 2017) to Bellam et al. therein
  149. 149.
    R. Bellam, N. R. Anipindi and D. Jaganyi, J. Mol. Liquids, 2018, 258, 57–65 LINK https://doi.org/10.1016/j.molliq.2018.02.122
  150. 150.
    A. M. Angeles-Boza, M. Z. Ertem, R. Sarma, C. H. Ibanez, S. Maji, A. Llobet, C. J. Cramer and J. P. Roth, Chem. Sci., 2014, 5, (3), 1141–1152 LINK https://doi.org/10.1039/C3SC51919H
  151. 151.
    G. Nord, B. Pedersen and E. Bjergbakke, J. Am. Chem. Soc., 1983, 105, (7), 1913–1919 LINK https://doi.org/10.1021/ja00345a040
  152. 152.
    E. E. Smith, “Aluminum Compounds in Food”, Paul B. Hoeber, New York, USA, 1928
  153. 153.
    J. Snow, Int. J. Epidemiol., 2003, 32, (3), 336–337 LINK https://doi.org/10.1093/ije/dyg153
  154. 154.
    A. Hardy, Int. J. Epidemiol., 2003, 32, (3), 337–340 LINK https://doi.org/10.1093/ije/dyg175
  155. 155.
    M. Dunnigan, Int. J. Epidemiol., 2003, 32, (3), 340–341 LINK https://doi.org/10.1093/ije/dyg160
  156. 156.
    N. Paneth, Int. J. Epidemiol., 2003, 32, (3), 341–343 LINK https://doi.org/10.1093/ije/dyg159
  157. 157.
    R. W. Chesney, Pediatr. Nephrol., 2012, 27, (1), 3–6 LINK https://doi.org/10.1007/s00467-011-2004-9
  158. 158.
    P. Mattsson, Vår Foda, 1981, 33, (6), 231–236
  159. 159.
    A. M. Coriat and R. D. Gillard, Nature, 1986, 321, (6070), 570 LINK https://doi.org/10.1038/321570a0
  160. 160.
    An article detailing the effects of various platinum metal species on the growth of water hyacinths provides a useful perspective (161); a Gillard-contemporaneous reference is (162) – but Gillard will have been aware of Margaret Farago’s work well before 1979
  161. 161.
    M. E. Farago and P. J. Parsons, Chem. Speciat. Bioavail., 1994, 6, (1), 1–12 LINK https://doi.org/10.1080/09542299.1994.11083218
  162. 162.
    M. E. Farago, W. A. Mullen and J. B. Payne, Inorg. Chim. Acta, 1979, 34, 151–154 LINK https://doi.org/10.1016/S0020-1693(00)94693-0
  163. 163.
    R. D. Gillard, and S. H. Laurie, ‘Metal-Protein Interactions’, in “Biochemistry of Food Proteins”, ed. B. J. F. Hudson, Ch. 5, Springer Science and Business Media, Dordrecht, The Netherlands, 1992, pp. 155–196 LINK https://doi.org/10.1007/978-1-4684-9895-0_5
  164. 164.
    Recent references testifying to continuing interest in the absorption of aluminium by tea plants, its concentration in their shoots and leaves, its extraction in tea infusions, and levels of aluminium in typical cups of tea include (165–167)
  165. 165.
    T. Karak and R. M. Bhagat, Food Res. Int., 2010, 43, (9), 2234–2252 LINK https://doi.org/10.1016/j.foodres.2010.08.010
  166. 166.
    M. Kröppl, M. Zeiner, I. J. Cindrić and G. Stingeder, Eur. Chem. Bull., 2012, 1, (9), 382–386 LINK https://doi.org/10.17628/ecb.2012.1.382-386
  167. 167.
    R. F. Milani, M. A. Morgano and S. Cadore, LWT – Food Sci. Technol., 2016, 68, 491–498 LINK https://doi.org/10.1016/j.lwt.2015.12.041
  168. 168.
    G. M. Wild, Nature, 1987, 326, (6112), 434 LINK https://doi.org/10.1038/326434c0
  169. 169.
    A typical example of the state of the controversy towards the end of the 20th century is provided by the linked references (170–172) – of which the last is of particular reference to the topic of aluminium in tea. The current situation can be traced through, for example (173–175)
  170. 170.
    D. G. Munoz, Arch. Neurol., 1998, 55, (5), 737–739 LINK https://doi.org/10.1001/archneur.55.5.737
  171. 171.
    W. F. Forbes and G. B. Hill, Arch. Neurol., 1998, 55, (5), 740–741 LINK https://doi.org/10.1001/archneur.55.5.740
  172. 172.
    V. Hachinski, Arch. Neurol., 1998, 55, (5), 742 LINK https://doi.org/10.1001/archneur.55.5.742
  173. 173.
    C. Exley, Environ. Sci.: Processes Impacts, 2013, 15, (10), 1807–1816 LINK https://doi.org/10.1039/C3EM00374D
  174. 174.
    A. Mirza, A. King, Claire Troakes and C. Exley, J. Trace Elem. Med. Biol., 2017, 40, 30–36 LINK https://doi.org/10.1016/j.jtemb.2016.12.001
  175. 175.
    A. Seidowsky, E. Dupuis, T. Drueke, S. Dard, Z. A. Massy and B. Canaud, Nephrol. Ther., 2018, 14, (1), 35–41 LINK https://doi.org/10.1016/j.nephro.2017.04.002
  176. 176.
    R. D. Gillard, Chem. Brit., 1985, 21, (6), 535
  177. 177.
    F. Linsker and R. L. Evans, J. Am. Chem. Soc., 1946, 68, (3), 403 LINK https://doi.org/10.1021/ja01207a019
  178. 178.
    Gillard does not cite sources for some of these claims, but implies that they were made in manuscripts submitted for him to referee – he was a commendably active peer reviewer. Several papers reporting preparations of a number of its complexes, including those of VO 2+, ZrO 2+, UO 2 2+, Sn 4+ and Th 4+ (see (179, 180) and references therein), appeared around this time. This group claimed to have prepared their 1,10-phenanthroline- N,N’-dioxide (phenO 2) ligand by hydrogen peroxide/glacial acetic acid oxidation of 1,10-phenanthroline, a method which works well for the conversion of 2,2’-bipyridine to its N,N’-dioxide (181) but is unlikely to be successful for the hoped-for analogous conversion of phen into phenO 2
  179. 179.
    A. K. Srivastava, S. Sharma and R. K. Agarwal, Inorg. Chim. Acta, 1982, 61, 235–239 LINK https://doi.org/10.1016/S0020-1693(00)89146-X
  180. 180.
    R. K. Agarwal and H. K. Rawat, Thermochim. Acta, 1986, 99, 367–371 LINK https://doi.org/10.1016/0040-6031(86)85300-X
  181. 181.
    P. G. Simpson, A. Vinciguerra and J. V. Quagliano, Inorg. Chem., 1963, 2, (2), 282–286 LINK https://doi.org/10.1021/ic50006a009
  182. 182.
    R. D. Gillard, Inorg. Chim. Acta, 1981, 53, L173 LINK https://doi.org/10.1016/S0020-1693(00)84786-6
  183. 183.
    R. D. Gillard, Inorg. Chim. Acta, 1989, 156, (2), 155 LINK https://doi.org/10.1016/S0020-1693(00)83488-X
  184. 184.
    S. Rozen and S. Dayan, Angew. Chem., Int. Ed., 1999, 38, (23), 3471–3473 LINK https://doi.org/10.1002/(SICI)1521-3773(19991203)38:23<3471::AID-ANIE3471>3.0.CO;2-O
  185. 185.
    The situation here recalls the difficulty of doubly-protonating 1,10-phenanthroline – see (186)
  186. 186.
    C. Swinnerton and M. V. Twigg, Trans. Met. Chem., 1978, 3, (1), 25–27 LINK https://doi.org/10.1007/BF01393498
  187. 187.
    F. Franks, “Polywater”, The Massachusetts Institute of Technology Press, Cambridge, USA, 1981
  188. 188.
    N. Fedyakin, Kollodniy Zhurnal, 1962, 24, 497–501
  189. 189.
    B. V. Derjaguin, Disc. Faraday Soc., 1966, 42, 109–119 LINK https://doi.org/10.1039/DF9664200109
  190. 190.
    B. V. Derjaguin, Z. M. Zorin, Ya. I. Rabinovich and N. V. Churaev, J. Colloid Interface Sci., 1974, 46, (3), 437–441 LINK https://doi.org/10.1016/0021-9797(74)90053-8
  191. 191.
    D. L. Rousseau, Am. Sci., 1992, 80, (1), 54–63 LINK https://www.jstor.org/stable/29774558
  192. 192.
    W. Gratzer, “The Undergrowth of Science: Delusion, Self-Deception and Human Frailty”, Oxford University Press, New York, USA, 2000, 328 pp
  193. 193.
    J. van Brakel, ‘Pure Chemical Substance’, in “Stuff: The Nature of Chemical Substance”, ed. K. Ruthenberg and J. van Brakel, Königshausen & Neumann, Würzburg, Germany, 2008, Ch. 9, pp. 145–162
  194. 194.
    A. M. V. S. V. Cavaleiro, J. D. Pedrosa de Jesus, V. M. S. Gil, R. D. Gillard and P. A. Williams, Trans. Met. Chem., 1982, 7, (2), 75–79 LINK https://doi.org/10.1007/BF00618186
  195. 195.
    A. M. V. S. V. Cavaleiro, J. D. Pedrosa de Jesus, V. M. S. Gil, R. D. Gillard and P. A. Williams, Inorg. Chim. Acta, 1990, 172, (1), 25–33 LINK https://doi.org/10.1016/S0020-1693(00)80445-4
  196. 196.
    I. Cavaco, J. Costa Pessoa, D. Costa, M. T. Duarte, R. D. Gillard and P. Matias, J. Chem. Soc., Dalton Trans., 1994, (2), 149–157 LINK https://doi.org/10.1039/DT9940000149
  197. 197.
    I. Cavaco, J. Costa Pessoa, S. M. Luz, M. T. Duarte, P. M. Matias, R. T. Henriques and R. D. Gillard, Polyhedron, 1995, 14, (3), 429–439 LINK https://doi.org/10.1016/0277-5387(94)00247-C
  198. 198.
    J. Costa Pessoa, M. J. Calhorda, I. Cavaco, P. J. Costa, I. Correia, D. Costa, L. F. Vilas-Boas, V. Félix, R. D. Gillard, R. T. Henriques and R. Wiggins, Dalton Trans., 2004, (18), 2855–2866 LINK https://doi.org/10.1039/B404305G
  199. 199.
    J. J. R. Frausto da Silva, R. Wootton and R. D. Gillard, J. Chem. Soc. A, 1970, 3369–3372 LINK https://doi.org/10.1039/B404305G
  200. 200.
    Analogous complexes can readily be prepared from other aromatic o-hydroxyaldehydes – see for example (201)
  201. 201.
    J. Costa Pessoa, I. Cavaco, I. Correia, R. D. Gillard, F. J. Higes, C. Madeira and I. Tomaz, Inorg. Chim. Acta, 1999, 293, (1), 1–11 LINK https://doi.org/10.1016/S0020-1693(99)00196-6
  202. 202.
    Ettling’s preparation of bis-salicylaldimine-copper(II), reported in 1840 (203), provided one of the earliest examples of a reaction of a coordinated ligand. Ettling wrote at length about salicylate(s) (203) in an oil steam-distilled (in 1835) from meadowsweet ( Spiraea ulmaria) flowers by the apothecary Pagenstecher and analysed by Löwig in Zürich (204, 205). Copper(II) and nickel(II) complexes of amino acid ester derivatives of salicaldehyde were described in (206)
  203. 203.
    C. Ettling, Justus Liebigs Ann. Chem., 1840, 35, (3), 241–276 LINK https://doi.org/10.1002/jlac.18400350302
  204. 204.
    K. J. Löwig, Ann. Phys., 1835, 112, (11), 383–403 LINK https://doi.org/10.1002/andp.18351121107
  205. 205.
    M. Vallett, J. Pharm. Sci. Access., 1836, 22, 187–200
  206. 206.
    P. Pfeiffer, W. Offerman and H. Werner, J. Prakt. Chem. (Leipzig), 1942, 159, 313–333
  207. 207.
    D. St. C. Black, in “Comprehensive Coordination Chemistry”, eds. G. Wilkinson, R. D. Gillard and J. A. McCleverty, Vol. 1, Pergamon Press, Oxford, UK, 1987, p. 434
  208. 208.
    D. St. C. Black, in “Comprehensive Coordination Chemistry”, eds. G. Wilkinson, R. D. Gillard and J. A. McCleverty, Vol. 6, Pergamon Press, Oxford, UK, 1987, p. 156
  209. 209.
    Gillard thought that the “adduct” of aniline with bis-paeonolatocopper(II) made by Pfeiffer and his students – see p. 174 of (210) for the copper-paeonol complex and its aniline solvate – was in fact probably a copper(II)-ketimine complex
  210. 210.
    P. Pfeiffer, E. Buchholz and O. Bauer, J. Prakt. Chem., 1931, 129, (1), 163–177 LINK https://doi.org/10.1002/prac.19311290112
  211. 211.
    The trivial name paeonol (US peonol, German päonol) for 4-methoxy-acetophenone dates from the time it was used in perfumery. It has also been used in traditional medicine – and, more recently, shown to have analgesic, anti-inflammatory. and anti-mutagenic properties. Pfeiffer’s laboratory studied its metal-complexing reactions in the 1920s (209, 212). The name paeonol was derived from the Greek – Paiõ̅n (Παιών) was Apollo’s title as physician of the gods. Presumably the perfumery usage of paeonol comes from the fragrance of paeony (Greek παιωνία) flowers
  212. 212.
    P. Pfeiffer, S. Golther and O. Angern, Chem. Ber., 1927, 60, (2), 305–313 LINK https://doi.org/10.1002/cber.19270600206
  213. 213.
    R. A. Wiggins and R. D. Gillard, 1970, unpublished
  214. 214.
    E. R. J. Sillanpää, A. Al-Dhahir and R. D. Gillard, Polyhedron, 1991, 10, (17), 2051–2055 LINK https://doi.org/10.1016/S0277-5387(00)86031-3
  215. 215.
    J. Costa Pessoa, S. M. Luz and R. D. Gillard, J. Chem. Soc., Dalton Trans., 1997, (4), 569–576 LINK https://doi.org/10.1039/A607374C
  216. 216.
    J. Costa Pessoa, T. Gajda, T. Kiss, J. J. G. Moura, I. Tomaz, J. P. Telo and I. Török . J. Chem. Soc., Dalton Trans., 1998, (21), 3587–3600 LINK https://doi.org/10.1039/A801888J
  217. 217.
    J. Costa Pessoa, I. Cavaco, I. Correia, D. Costa, R. T. Henriques and R. D. Gillard, Inorg. Chim. Acta, 2000, 305, (1), 7–13 LINK https://doi.org/10.1016/S0020-1693(00)00102-X
  218. 218.
    R. D. Gillard, A. M. Pollard, P. A. Sutton and D. K. Whittaker, Archaeometry, 1990, 32, (1), 61–70 LINK https://doi.org/10.1111/j.1475-4754.1990.tb01082.x
  219. 219.
    A. M. Child, R. D. Gillard and A. M. Pollard, J. Arch. Sci., 1993, 20, (2), 159–168 LINK https://doi.org/10.1006/jasc.1993.1011
  220. 220.
    R. D. Gillard, S. M. Hardman, R. G. Thomas and D. E. Watkinson, Stud. Conserv., 1994, 39, (2), 132–140 LINK https://doi.org/10.1179/sic.1994.39.2.132
  221. 221.
    R. D. Gillard, S. M. Hardman, R. G. Thomas and D. E. Watkinson, Stud. Conserv., 1994, 39, (3), 187–192 LINK https://doi.org/10.1179/sic.1994.39.3.187
  222. 222.
    Indeed one paper was concerned with both subjects – (223) dealt with rhodium(III) complexes with enantiomers of nicotine
  223. 223.
    R. D. Gillard and E. Lekkas, Trans. Met. Chem., 2000, 25, (6), 617–621 LINK https://doi.org/10.1023/A:1007088115719
  224. 224.
    This final paper (198) and his 1999 paper on the same complexes (201), reflect both his long-standing interest in complexes of aminoacids and their derivatives and his fruitful Portuguese collaborations. These two papers also complement Part IV of Gillard’s “Oxovanadium(IV) – Amino-Acids” series ( Table S11) on oxovanadium complexes of cysteine and of penicillamine (225)
  225. 225.
    J. Costa Pessoa, L. F. Vilas Boas and R. D. Gillard, Polyhedron, 1990, 9, (17), 2101–2125 LINK https://doi.org/10.1016/S0277-5387(00)84041-3
  226. 226.
    To quote from the abstract and text of this article: “…characterised by elemental analysis, spectroscopy (UV-VIS, CD, EPR), TG, DSC and magnetic susceptibility measurements (9–295 K) . the use of molecular mechanics and density functional calculations… DFT calculations for both types of tautomers…”
  227. 227.
    As was recently stated “Bob was an undervalued member of the generation who brought coordination chemistry to the front of scientific awareness.” – see page 303 of (228)
  228. 228.
    G. B. Kauffman, “Alfred Werner: Founder of Coordination Chemistry”, Springer-Verlag, Heidelberg, Germany, 1966
  229. 229.
    G. B. Kauffman, Coord. Chem. Rev., 1972, 9, (3–4), 339–363
  230. 230.
    (231). The first edition was published in 1915 by J. & A. Churchill (London) under the title “The Chemistry of Cyanogen Compounds”
  231. 231.
    H. E. Williams, “Cyanogen Compounds”, 2nd Edn., E. Arnold and Co, London, UK, 1948
  232. 232.
    It is a matter of considerable regret that Gillard did not write a book on chemistry. A volume on coordination complexes which combined an outline of their historical context with accounts of their preparation, characterisation and properties, would have been particularly valuable and appreciated, as would a book expanding his review on circular dichroism ( cf. (233))
  233. 233.
    R. D. Gillard, ‘The Cotton Effect in Coordination Compounds‘, in “Progress in Inorganic Chemistry”, ed. F. A. Cotton, Vol. 7, John Wiley and Sons Inc, New York, USA, 1966, pp. 215–276 LINK https://doi.org/10.1002/9780470166086.ch4
  234. 234.
    (235). This obituary also mentions a popular public lecture entitled “Is God left handed?”, reflecting his long standing fascination by chirality and an unpublished essay on chemistry in Sherlock Holmes books
  235. 235.
    I. Gillard and F. Hammett, ‘Robert David Gillard (1956)’, St Edmund Hall Magazine (Oxford), 2013, 18, (4), 167–173

4. Acknowledgements

Thanks are due to the many people who provided a tremendous amount of information, material and reminiscences about Gillard. These include the late Brice Bosnich, Tony Addison, the late Malcolm Green, Michael Mingos, Brian Heaton, John Jones, Ed Constable, Jon McCleverty, Bill Griffith, the late Tony Poë, Nicholas Payne and the late Paul O’Brien. We are most grateful to Colin Hubbard for reading the manuscript in various stages of preparation and for providing many valuable comments, to Nick Davidson and Gillian Powell for information on Gillard’s time in St Edmund Hall, to John Todd for searching the early records of the University of Kent for information relevant to Gillard’s time in Canterbury, to Daniel Flowerday for details of the 1981 platinum group metals conference in Bristol, and to Leslie Sims for providing details of the Cwmbach Male Voice Choir. Special thanks are due to Gillard’s daughter Fiona Hammett, his first wife Mrs Diane Gillard, and his second wife the late Mrs Anne Gillard for family details. Several people provided photographs of considerable interest and those included in each of the present articles are acknowledged in the Figure captions.

5. Supplementary Material

The Supplementary Tables S1–S12 may be found in the Supplementary Information included with the online version of Part I (86).

The authors have full listings of the publications in each of the multi-part series, and a preliminary version of a complete bibliography. Any reader wishing to acquire any of these should contact either of the authors. Anyone wishing to know more about the historical background to Gillard’s brief letter on the question of the toxicity of aluminium in tea, or consult a timeline for the dinitrate anion, [(NO3)2H]−, is invited to email Dr Burgess via the Editorial Office.

The Authors


After grammar school (Queen Elizabeth’s, Barnet), National Service (Royal Artillery), and Cambridge (Sidney Sussex; MA, PhD on inorganic kinetics) John Burgess started work at Fisons Fertilizers in Suffolk. Two years later he embarked on an ICI Fellowship at the University of Leicester which led to three decades of teaching and research – ranging from mechanisms to solvatochromism to biochemistry, linked by solution chemistry of iron complexes. He is now Emeritus Reader in Inorganic Chemistry at the University of Leicester, combining the preparation of an expanded version of “Color of Metal Compounds” with gardening and pursuing his interests in music, East Anglian churches and railways.


Martyn Twigg did inorganic reaction mechanisms graduate research in a laboratory next to Gillard’s office at Canterbury. After fellowships at Toronto and Cambridge and being headhunted into the ICI Corporate Laboratory he moved to ICI Billingham to work on industrial process catalysts. Later at Johnson Matthey he was responsible for autocatalyst development and production at Royston. After emissions control successes he retired in 2010 and continues research with universities in the UK and overseas with honorary positions at some. His catalyst development, manufacturing and consulting business is thriving with novel catalytic systems in production.

Read more of this issue

Related articles

Dennis Dowden and the Development of Catalytic Science

View
Download

362 KB

Professor Robert D. Gillard: Transition Metal Chemist 1936–2013: Part I

View
Download

1.2 MB

MORE ARTICLES

Find an article

ArticleSearch