REDOX CHEMISTRY OF TRINUCLEAR COMPLEXES POSSESSING A HEXATHIOLATOMOLYBDATE(IV) CORE - INSITU SYNTHESES, CHARACTERIZATION AND GEOMETRY OPTIMIZATION

The trinuclear heterobimetallic clusters [(Ph3P)Cu(mu-SR)3Mo(mu-SR)3Cu (PPh3)] (R = C6H4Me-4 2, C6H4F-4 3, C6H4Cl-4 4 or C6H4Br-4 5) have bee n found to undergo reversible one-electron reductions. The reduction p otential is sensitive to the para substituent on the thiolate and has been correlated with the electron-donating properties of the substitue nt. In addition, 2 undergoes a reversible one-electron oxidation. Acco rding to EPR measurements, the oxidation of 2 is molybdenum-based. Geo metry optimizations based on density functional theory of the oxidized and reduced model cluster [(H3P)Cu(mu-SH)3Mo(mu-SH)3Cu(PH3)], assumin g retention of the D3 point-group symmetry, have shown that both redox processes will lead to an elongation of the Mo-Cu vector. Reduction o f the central molybdenum fragment will decrease the strength of the Cu to Mo donor bond. Oxidation of the central molybdenum fragment will r esult in a decrease of electrostatic interaction with the [(H3P)CuCu(P H3)]2+ fragment. The reaction of 2 with NOBF4 results in oxidation of the cluster. The IR spectrum of the diamagnetic reaction product shows a band at 1657 cm-1 suggesting the presence of co-ordinated NO-. Furt her evidence is provided by N-14 NMR spectroscopy. The reactions of 2 and 5 with arenediazonium salts result in degradation of the clusters, with the liberation of organic sulfides and disulfides, suggesting th e involvement of free thiyl radicals.