Crystal structures, spectroscopy and magnetism of Cu(II) bromide adducts with bis(2-benzimidazolyl)alkanes: influence of alkyl bridge on the degree of distortion from tetrahedral

The spectroscopic and magnetic measurements of three mononuclear copper(II) bromide compounds with the ligands bis(2-benzimidazolyl)ethane (abbreviate d as dbz), bis(2-benzimidazolyl)propane (abbreviated as tbz) and bis(2-benz imidazolyl)butane (abbreviated as qbz) and the general formula [Cu(L)Br-2] (in which L = dbz, tbz or qbz) have been determined, together with the X-ra y structure of two of the three compounds. Each compound has a tetrahedrall y based CuN2Br2 chromophore with Cu-N distances from 1.976(3) to 1.993(11) Angstrom and Cu-Br distances from 2.356(2) to 2.3982(7) Angstrom. Angles N- Cu-N and Br-Cu-Br vary from 94.44(13) to 105.5(4)degrees and from 97.88(2) to 98.94(8)degrees, respectively. The length of the alkane chain determines the degree of tetragonality and the EPR measurements at 77 K as a frozen s olution reveal a d(x2-y2) for the copper compounds with the ligands dbz and qbz and a d(z2) ground state with the copper tbz compound. The dihedral an gles are 52.6(3) and 67.8(4)degrees for compounds [CuBr2(dbz)] and [CuBr2(t bz)], respectively. (C) 2000 Elsevier Science S.A. All rights reserved.