GOLD AND PLATINUM MOLECULAR CLUSTER COMPOUNDS STUDIED BY AU-197 MOSSBAUER-SPECTROSCOPY

The technique of Au-197 Mossbauer absorption spectroscopy has been use d to study four varieties of the high nuclearity gold molecular cluste r compounds abbreviated as Au-55, all having a cuboctahedral structure , with 12 PPh3-ligands or modifications of PPh3. The technique of emis sion spectroscopy developed in our laboratory [1] has been applied to four different molecular platinum carbonyl cluster compounds of varyin g 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 si te of the water soluble version differ strongly due to the effect of N a+ on the Au-Cl distances. In the frozen solution, the effect of the i onic charge on this cluster can be clearly seen. The similarity of the spectra of all the Pt compounds, especially the occurrence of a subst antial singlet contribution in all spectra, is explained by a coalesci ng mechanism for the low-nuclearity clusters, induced by the neutron i rradiation damage inflicted while preparing the sample as Mossbauer so urces. The observed decrease of the absorption intensity with increasi ng temperature is evidence for a cluster character of the sample remai ning after neutron irradiation.