Dimeric copper(II) compounds with a tripodal imidazole-containing ligand and bridged by imidazolate, benzimidazolate, and benzotriazolate ions. Crystal and molecular structure of µ-(benzotriazolato-N1,N3)bis{[tris(N1-methylbenzimidazol-2-ylmethyl)amine-N,N3,N3′,N3″]copper(II)} trinitrate

Abstract

A series of dimeric copper(II) co-ordination compounds with general formula [Cu₂(tmbma)₂(azolate)]X₃ has been prepared and characterized, where tmbma is the tripodal benzimidazole-containing ligand tris(N-methylbenzimidazol-2-ylmethyl)amine, azolate is the anion of imidazole, benzimidazole, or benzotriazole, and X = NO₃^–, BF₄^–, or ClO₄^–. Variable-temperature magnetic susceptibility measurements indicate antiferromagnetic interactions with J values of –10 to –18 cm^–1(for the benzimidazolate and benzotriazolate compounds) and –28 cm^–1(for the imidazolate compounds). Q-Band and X-band e.s.r. spectra show typical S= 1 signals; D values calculated from these spectra range from 0.08 to 0.13 cm^–1. The crystal and molecular structure of the title compound has been determined by single-crystal X-ray diffraction. The compound crystallizes in the space group C2/c, with a= 16.880(2), b= 26.011(1), c= 14.686(1)Å, β= 100.585(7)°, and Z= 4. The structure was solved by heavy-atom methods and refined using least-squares techniques to a residual R of 0.050 for 3 327 reflections with l > 2σ(l). The structure consists of dimeric cations, having C₂ symmetry, and disordered nitrate anions; the co-ordination geometry around the copper ions can be described as distorted trigonal bipyramidal with three equatorial benzimidazole nitrogen atoms, one axial amine nitrogen atom, and the benzotriazolate ion bridging from an axial position on one copper ion to an axial position on the other copper ion, resulting in a Cu ⋯ Cu distance of 5.536(2)Å.