Isomerism and unusual magnetic behaviour of some benzimidazole complexes of nickel(II)

Abstract

The preparation is described of the compounds NiL₄X₂, where L = benzimidazole, X = Cl, Br, I, or ClO₄. The iodide and perchlorate are diamagnetic; the bromide exists in three isomeric forms, two paramagnetic and one diamagnetic, and the chloride as two paramagnetic isomers. The acetone (= S) solvates NiL₄Cl₂,S, NiL₄Cl₂,S₂(three isomers), and NiL₄Br₂,S₂ have also been isolated. The electronic spectra of these compounds have been obtained at room temperature and at ca. 80°K, and their magnetic properties have been studied over a temperature range.

The diamagnetic complexes contain planar NiL₄ units, whereas the paramagnetic compounds are hexacoordinate, but with pronounced distortions from an octahedral configuration. Several of the compounds display unusual magnetic behaviour. The blue form of NiL₄Cl₂,S₂ is magnetically normal, but the green form is antiferromagnetic, with a temperature-dependent exchange integral. The nickel ion in the third complex of this stoicheiometry appears to have a spin-singlet ground state with a thermally accessible spin-triplet level. One form of the compound NiL₄Br₂ has a temperature-independent susceptibility of ca. 2770 × 10^–6 c.g.s.u./mole over the range 300–80°K.