CORRELATION OF MO-95 NMR CHEMICAL-SHIFTS, ELECTRONIC ABSORPTION-BANDS, AND SOLVENT DONOR NUMBERS FOR SOME DIMERIC MO-2(O2CR)(4)L-2 SOLVENT ADDUCTS

The Mo-95 NMR chemical shifts are reported for two series of solvent a dducts of the dimeric molybdenum(II) complexes Mo-2(O2CR)(4)L-2 (R = C F3, Bu-t; L = solvent). The large deshielding effect (over 450 ppm for the R = CF3 series as the solvent changes from chloroform to hexameth ylphosphoramide) correlates well with the donor number of the solvent. The lowest energy electronic absorption band corresponding to the del ta-delta transition also moves to longer wavelength with the more str ongly coordinating solvents, which is consistent with weakening of the Mo=Mo quadruple bond and the dominance of the Delta E parameter in th e paramagnetic term which controls the magnitude of delta(Mo-95). (C) 1997 Elsevier Science Ltd.