Johnson Matthey Technology Review - Volume 58, Issue 3, 2014

To evaluate future applications of metallic clusters in nanoscience and nanotechnology, the electronic properties of the high-nuclearity carbonyl anionic platinum cluster [Pt19(CO)22]^4– were investigated using two different organic cations. In particular, N,Nʹ-diethyl viologen dication (Vio²⁺) and N,Nʹ-dimethyl-9,9ʹ-bis-acridinium dication (Acr²⁺) were employed as counterions, oxidising agents and characterisation probes. The reactions of [Pt19(CO)22]^4– tetra-n-butylammonium salt, (TBA⁺)4([Pt19(CO)22]^4–), with both (Vio²⁺) and (Acr²⁺), used as tetraphenylborate salts, yielded two new compounds, which were isolated. The stoichiometries and properties of these new compounds were determined and compared on the basis of infrared (IR) solution spectra, electron spin resonance (ESR) analyses, fluorometric spectra, superconducting quantum interference device (SQUID) magnetometry and resistivity measurements. For Vio²⁺, a cation-exchange reaction produced the final compound (Vio²⁺)2([Pt19(CO)22]^4–), ‘PtVio’, which was structurally characterised by single crystal X-ray diffraction (XRD) analysis. However, when using Acr²⁺, a spontaneous redox reaction occurred and a (Acr⁺)(TBA⁺)2([Pt19(CO)22]^3–) stoichiometry for the precipitated solid, ‘PtAcr’, was inferred from the experimental evidence, leading to an interesting ‘doubly-radicalic salt’. This new type of salt, consisting of a radical anionic Pt cluster and a radical cation, is characterised by extremely simple synthesis and isolation processes and by the lowest solid-state resistivity found in high-nuclearity cluster salts with redox-active cations (1).

This review briefly describes the vacuum electrostatic levitation furnace developed by JAXA and the associated non-contact techniques used to measure the density, the surface tension and the viscosity of materials. The paper then presents a summary of the data taken with this facility in the equilibrium liquid and non-equilibrium liquid phases for the six platinum group metals (pgms): platinum, palladium, rhodium, iridium, ruthenium and osmium over wide temperature ranges that include undercooled and superheated phases. The presented data (density, surface tension and viscosity of Pt, Rh, Ir, Ru and Os and density of Pd) are compared with literature values.

Having established that osmium is the densest metal at room temperature the question arises as to whether it is always the densest metal. It is shown here that at ambient pressure osmium is the densest metal at all temperatures, although there is an ambiguity below 150 K. At room temperature iridium becomes the densest metal above a pressure of 2.98 GPa, at which point the densities of the two metals are equal at 22,750 kg m^–3.

In the twentieth century Dennis Albert Dowden, affectionately referred to as DAD by friends and colleagues, was an important figure in the development of an understanding of the structure of industrial heterogeneous catalysts, the species present and the processes taking place on them. He was born in Bristol, UK, and following education at the University of Bristol and a short period at Amherst College in the USA, in 1938 he joined Imperial Chemical Industries (ICI) at Billingham in the North East of England. He worked there on catalysis, catalyst manufacture and catalytic processes for the next thirty-seven years. His major contribution was to bring a wide range of sciences and a rational approach into what had been until then regarded as “black art”, capable of only empirical analysis. His influence extended across ICI, which at that time operated many industrial catalytic processes, and academically he was influential worldwide and especially in the USA.

Here we profile an upcoming researcher who has benefitted from Johnson Matthey’s support in the past. David Nelson is a newly appointed Chancellor’s Fellow and Lecturer at the University of Strathclyde, in Glasgow, UK. His research interests concern the development of useful transition metal catalysed processes for synthesis via a detailed understanding of mechanism, rate and selectivity in key steps.