Synthesis and ligand-based mixed valency of cis- and trans-CrIII(X4SQ)(X4Cat)(L)n (X = Cl and Br, n=1 or 2) complexes:: Effects of solvent media on intramolecular charge distribution and ligand dissociation of CrIII(X4SQ)3

The treatment of CrIII(X(4)SQ)(3) (SQ = o-semiquinonate; X = Cl and Br) with acetonitrile affords trans-Cr-III(X(4)SQ)- (X(4)Cat)(CH3CN)(2) (X = Cl (1) and Br (2)). In the presence of 2,2'-bipyridine (bpy) or 3,4,7,8-tetramethyl-1,10-phenanthrene (tmphen), the reaction affords Cr-III(X(4)SQ)(X(4)Cat)(bpy)(.)nCH(3)CN (X = Cl, n = 1 (3); X = Br, n = 0.5 (4)) or Cr-III(X(4)SQ)(X(4)Cat)(tmphen) (X = Cl (5) and Br (6)), respectively. All of the complexes show a ligand-based mixed-valence (LBMV) state with SQ and Cat ligands. The LBMV state was confirmed by the presence of the interligand intervalence charge-transfer band. Spectroscopic studies in several solvent media demonstrate that the ligand dissociation included in the conversion of Cr-III(X(4)SQ)(3) to 1-6 occurs only in solvents with relatively high polarity. On the basis of these results, the effects of solvent media were examined and an equilibrium, Cr-III(X(4)SQ)(3) Cr-III(X(4)BQ)(X(4)SQ)(X(4)Cat) (BQ = o-benzoquinone), is proposed by assuming an interligand electron transfer induced by solvent polarity.