Ligand effects on the delta->delta 6* band energies and intensities in a series of diimine complexes of dimolybdenum

The complexes Mo(2)X(4)(diimine)(2) (X = Cl, Br, I and diimine = 2,2'-bipyridine, 4,4'-dimethyl-2,2'-bipyridine, 2,2'-bipyrazine, 3,3'-bipyridazine, 2,2'-bipyrimidine, 1,10-phenanthroline and 4,7-diphenyl-1,10-phenanthroline) have been prepared by reaction of Mo-2 (OAc)(4) with (CH3)(3)SiX in the presence of excess diimine. The product complexes apparently contain non-bridged quadruple molybdenum-molybdenum bonds. Each molybdenum is coordinated to a bidentate diimine and two halogen atoms. Electronic absorption and electrochemical studies have shown that shifts in the energy of the delta --> delta* band are affected by the mixing of this transition with a metal-to-ligand charge transfer transition, probably a delta --> pi* transition. It was also found that the compounds Mo(2)X(4)(diimine), react slowly with oxygen to form Mo2O4Cl4(diimine)(2) and then MoO2Cl2(diimine). The crystal and molecular structure of MoO2Cl2 (4,4'-dimethyl-2,2'bipyridine), determined by a three-dimensional X-ray diffraction study, is reported. Copyright (C) 1996 Elsevier Science Ltd