Mononuclear and Mixed-Valence Binuclear Oxovanadium Complexes with Benzimidazole-Derived Chelating Agents

Oxovanadium complexes with H2bzimpy (2,6-bis[benzimidazol-2‘-yl]pyridine) and Me2bzimpy (2,6-bis[N‘-methylbenzimidazol-2‘-yl]pyridine), and H3ntb (tris[benzimidazol-2‘-yl-methyl]amine) and Me3ntb (tris[N‘-methylbenzimidazol-2‘-yl-methyl]amine) have been synthesized. Dioxovanadium(V) and oxovanadium(IV) complexes prepared from
H2bzimpy and Me2bzimpy are [VVO2(Hbzimpy)]·1.25H2O (1), [VVO2(Me2bzimpy)](ClO4)·H2O (3), [VIVO(H2bzimpy)(H2O)2](CF3SO3)2·2H2O (2), and [VIVO(Me2bzimpy)(H2O)2](CF3SO3)2 (4). H3ntb and Me3ntb afforded oxovanadium(IV) complexes, [VIVO(Hntb)]·2MeOH (5), [VIVO(H3ntb)Cl]Cl·H2O (7), [VIVO(Me3ntb)SO4]·H2O (9), [VIVO(Me3ntb)Cl]Cl·H2O (10), and mixed-valence complexes, [(H3ntb)VIVO(μ-O)VVO(H3ntb)](CF3SO3)3·2H2O (8) and [(Me3ntb)VIVO(μ-O)VVO(Me3ntb)](CF3SO3)3·3H2O (11). Crystal structures of 2, 7, and 11 are reported. The mixed-valence complexes,
8 and 11, show 15-line isotropic ESR spectra in fluid solutions at room temperature. These compounds also exhibit
an intervalence transfer band around 1015 nm which is essentially independent of solvent, so these compounds
are stable, mixed-valence species where the single unpaired electron is delocalized over the two vanadium centers
at ambient temperature. With respect to one-electron reduction, the dioxovanadium(V) complexes are redox-potential
equivalent with their monooxovanadium(IV) counterparts.