Cobalt(II) and zinc(II) complexes of the 'tripod' ligand tris(2-benzimidazylmethyl)amine. Some five-coordinate derivatives and some with mixed stereochemistries

Abstract

A series of cobalt(II) and zinc(II) complexes of the title ligand are reported which contain mixed stereochemistries, e.g., five-coordinate trigonal bipyramidal cations [M(ligand)X]+, and four-coordinate anions, [MX4]2− (M = Co, Zn; X = Cl, Br, NCS). The blue cobalt complexes, [Co(ligand)X]2[CoX4], are readily converted to purple five-coordinate complexes, [Co(ligand)X]X, by recrystallisation from a solvent containing water, e.g. acetone. Other five-coordinate cobalt and zinc derivatives were also prepared, [Co(ligand)X]X (X = NO3, ClO4), [Co(ligand)X]BPh4 (X = Cl, Br, NCS, NO3, ClO4), [Zn(ligand)X]BPh4 (X = Cl, Br, I, NCS). Nuclear magnetic resonance data for all the zinc complexes indicate a significant deshielding of one benzene ring proton on each coordinated benzimidazole group. Conductance data suggest the possibility of cationic association through pseudo-hydrogen bonding in both the cobalt and zinc derivatives involving Cl, Br, NCS anions.