Ligand-controlled nuclearity in nickel bis(benzimidazolyl) complexes

A series of nickel complexes supported with a tripodal ligand bis(1-methylbenzimidazolyl-2-methyl)amine (L) or bis(1-methylbenzimidazolyl-2-methyl)-10-camphorsulfonamide (L′) on a Ni(ii) ion were synthesized and fully characterized. The complexes, [LNiCl(µ-Cl)]₂·4CH₃OH (1), [LNi(CH₃CN)₃](ClO₄)₂·2CH₃CN (3), and [L₂Ni₂(µ-OAc)₃]X (X = Cl⁻ (5) or ClO₄⁻ (7)), coordinated with the tridentate L ligand, all possess an octahedral structure at the nickel center; in contrast, the geometry of the complexes, L′NiCl₂ (2), [L′Ni(CH₃CN)₃](ClO₄)₂·2CH₃CN (4), and L′Ni(OAc)₂·0.5Et₂O (6), employing the L′ ligand are either tetrahedral or octahedral. Due to the weak coordinating ability of the sulfonamide group and the steric hindrance of the camphorsulfonyl group of L′, the tripodal L′ becomes a bidentate ligand in the presence of chloride or acetate groups, which have a stronger electron donating ability than acetonitrile, bound to the nickel center. It is noteworthy that the nuclearity of the nickel complexes can be controlled by the coordination ability of the central nitrogen of the supporting bis-methylbenzimidazolyl ligand.