Platinum Metals Review - Volume 48, Issue 3, 2004

Magnus’ green salt is a quasi-one-dimensional compound of composition [Pt(NH3)4][PtCl4] comprising linear arrays of platinum(II) ions. It is essentially insoluble in water and organic solvents and therefore difficult to process, which limits its use. Recently, soluble and thus processible derivatives of Magnus’ green salt have been synthesised by substituting the ammonia by linear and branched aminoalkanes. The Pt-Pt distances and the properties of these Magnus’ salt derivatives depend on the detailed structure of the aminoalkane. In particular, in compounds with branched aminoalkanes weak but noteworthy interactions arise between adjacent platinum atoms, as is evident from their colour, their electrical conductivity, and their UV and IR spectra. Compounds with optically active branched aminoalkanes exhibit circular dichroism with a bisignate Cotton effect and unusually high absolute values for the chiral anisotropy factors. The complex [Pt(NH2dmoc)4][PtCl4] with dmoc designating (S)-3,7-dimethyloctyl is of particular importance since its colour and electrical conductivity strongly resemble those of Magnus’ green salt. Films of [Pt(NH2dmoc)4][PtCl4] can function as an active semiconducting layer in field effect transistors. Remarkably, such devices have superior stability in air and water to unprotected field effect transistors fabricated with typical organic polymers. Hence, Magnus’ salt derivatives might find use in components of mass-produced “plastic electronics”.

This review focuses on the reactions of ethanol on the surfaces of platinum, palladium, rhodium and gold supported on ceria (of size 10-20 nm). The bimetallic compounds: Pt-Rh, Rh-Au, Rh-Pd, and Pt-Pd were also investigated. Initially this work was aimed at understanding the roles of the different components of automobile catalytic converters on the reactions of ethanol, which is used as a fuel additive. Some of the catalysts that showed high activity for ethanol oxidation were also investigated for hydrogen production. The addition of any of the above metals to CeO2 was found to suppress the oxidation of ethanol to acetates at room temperature, as there are fewer surface oxygen atoms available to oxidise the ethanol (the remaining oxygen atoms did not produce efficient oxidation). Ethanol dehydrogenation to acetaldehyde was facilitated by the presence of Pt or Pd; at higher temperatures the acetaldehyde condensed to other organic compounds, such as crotonaldehyde. By contrast, in the presence of Rh only traces of acetaldehyde or other organic compounds were seen on the surface, and detectable amounts of CO were found upon ethanol adsorption at room temperature. This indicates the powerful nature of Rh in breaking the carbon-carbon bond in ethanol. The effects of prior reduction were also investigated and clear differences were seen: for example, a shift in reaction selectivity is observedfor the bimetallic Rh-containing catalysts. Methane was the dominant hydrocarbon on the reduced catalysts while acetaldehyde was the main product for the nonreduced ones. Hydrogen formation was monitored during steady state ethanol oxidation and Pt-Rh and Rh-Au were found to be the most active catalysts.

Piezochromic phenomena are explained by pressure perturbation to the HOMO and/or LUMO energy levels of the related electronic transition. The piezochromism of solid inorganic and organic materials has been investigated by examination of the phase transition phenomena. Specific electronic properties of the solids, acquired by tuning the external pressure, may be used as electronic devices and as pressure sensors. The effects of pressure perturbations on the absorption and emission spectra exhibited by solid palladium complexes are reviewed here. Related phenomena exhibited by platinum complexes and other metal complexes are included for comparison.

A flowsheet has been developed for the production of rich concentrates of precious and non-ferrous metals by a complex treatment of the flotation products from South African platinum-containing chrome ores. The procedure involves: autoclave leaching, roasting, hydrochlorination and precious metal recovery by sorption. Autoclave oxidative leaching of the initial material allows the non-ferrous metals to pass into solution from where they are recovered as a rich sulfide concentrate (> 30% nickel and copper). Recovering the precious metals into solution combines two operations: sinter roasting and hydrochlorination. Roasting destroys the precious metal acid-proof mineral forms. The precious metals are recovered from solution by ion exchange using anionites that are finally burned. The ash from the burning is a concentrate of precious metals (> 75% in total) which are recovered in three forms: ammonium chloroplatinate with purity > 98%, palladium dichlorodiamine with purity > 96%, and a mixture of rhodium, ruthenium and iridium hydrates. The flowsheet uses full water rotation and minimum consumption of reagents, and gives a good recovery of metals to commodity concentrates (nickel > 98%, copper > 80% and precious metals (in total) > 95%).

It is not known for certain howfour platinum roubles came to be in Johnson Matthey ’s possession. There is rumour that, at the end of World War I, A. B. Coussmaker of Johnson Matthey, negotiated with the White Russians to smuggle out of Russia a hoard of coins which had been withdrawn by the government years before. The hoard was reputed to be on a train to the West when the Reds caught up with it. Rather than stop the transaction, they thought it a good idea as it would raise capital for them - at that time, the refining capacity of the young U.S.S.R. had been disrupted. So they took over the deal and let the consignment continue its journey to Johnson Matthey where it was refined and the platinum sold on their behalf. However, this is speculation (1). Eye witnesses state that two roubles were definitely in the company’s possession in 1956, and that two more came from the desk of Dr Leslie B. Hunt, the founder of this Journal (1). The roubles have thus been in Johnson Matthey ’s possession for almost 50 years and probably for longer. More likely to be true is a brief note in a typewritten statement in the possession of Johnson Matthey, stating no more than “the specimens formed part of a consignment sent to Johnson Matthey for refining about 1870” (2). As there is always interest in platinum coins and particularly in Russian roubles which were the first platinum coins to be minted, it was decided to investigate the metal content of the Johnson Matthey roubles to find if they conformed to recognised Russian roubles - or were forgeries.