Structural and spectroscopic characterisation of tris(2-benzimidazolylmethyl)amine coordination compounds of Zn(II), Cd(II) and Hg(II)

Zinc(II), cadmium(II) and mercury(II) coordination compounds derived from tris(2-benzimidazolylmethyl)amine (ntb) were characterised by 1H and 13C NMR in solution, IR and X-ray single crystal diffraction for [Zn(ntb)Cl]2[ZnCl4]4EtOH, [Cd(ntb)(?2-NO3)]NO32DMSO and [Hg(ntb)Cl]2[HgCl4]4EtOH. The complexes derived from zinc(II), cadmium(II) and mercury(II) halides form [M(ntb)X]+ cations, where the metal ions are pentacoordinated and have a distorted trigonal bipyramidal geometry, with tetrahedral anions [MX4]2?. In the [Cd(ntb)(?2-NO3)]NO32DMSO complex, by analogy with the Zn(II) and Hg(II) compounds, the NO3 ? could be considered as the fifth apical substituent in a distorted trigonal bipyramid geometry. In all complexes the ligand is coordinated to the metal through the imidazolic nitrogen atoms and has a weak coordination with the tertiary amine. The counter ion (halide or nitrate) remains bonded to the metal ion in solution and in the solid state as was evidenced by NMR and X-ray diffraction. The structures presented interactions between the coordinated counterion and the nearest C?H of the aromatic rings. All cations show an approximate C3 symmetry. The distortions found in the solid state were attributed to intermolecular hydrogen bonding and stacking between the benzimidazolic rings of neighbouring molecules.