SYNTHESIS AND CHARACTERIZATION OF HETEROMETALLIC CARBONYL CLUSTER ANIONS

The chemistry of rhodium carbonyl cluster anions is a guide-line for the rational synthesis of those mixed-metal clusters which contain rhodium associated with a metal of group VIII. The work presented here concerns reductions of neutral carbonylic substrata and redox condensations, performed under a carbon monoxide atmosphere which limits the nuclearity to 6-7 metal atoms and induces metal redistribution amongst the various species. The reduction degree of a species (i.e. the ratio anionic charge/metal atoms) is a function of the reducing strength (or basicity) of the medium and can be chosen with some accuracy, while the internal Rh:M ratio may be addressed working on the solution equilibria. Several M-Rh species (M = Fe, Ru, Os, Ir, Pt) have been specifically synthesized yielding the MRh4, and MRh5 families of homologous compounds where rhodium prevails as the main component of the metal skeleton. As a consequence the main structural and physical properties of these species are always strictly related to those of the corresponding homometallic rhodium species. On the other hand, the presence of the M heterometal acts as a 'fine tuner' giving to any member of these families specific properties, such as the reactivity and the NMR chemical shifts.