Gold and platinum molecular cluster compounds studied by Au-197 Mossbauer spectroscopy

The technique of Au-197 Mossbauer absorption spectroscopy has been used to study four varieties of the high nuclearity gold molecular cluster compounds abbreviated as Au-55, all having a cuboctahedral structure, with 12 PPh3-ligands or modifications of PPh3. The technique of emission spectroscopy developed in our laboratory [1] has been applied to four different molecular platinum carbonyl cluster compounds of varying cluster nuclearity, abbreviated as Pt-38, Pt-26, Pt-24, and Pt-19 [2]. The four Au-55 compounds were studied, both as dry materials and as frozen solutions. The Mossbauer parameters of the chlorine ligated site of the water soluble version differ strongly due to the effect of Na+ on the Au-Cl distances. In the frozen solution, the effect of the ionic charge on this cluster can be clearly seen. The similarity of the spectra of all the Pt compounds, especially the occurrence of a substantial singlet contribution in all spectra, is explained by a coalescing mechanism for the low-nuclearity clusters, induced by the neutron irradiation damage inflicted while preparing the sample as Mossbauer sources. The observed decrease of the absorption intensity with increasing temperature is evidence for a cluster character of the sample remaining after neutron irradiation.