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 (abbreviated as dbz), bis(2-benzimidazolyl)propane (abbreviated as tbz) and bis(2-benzimidazolyl)butane (abbreviated as qbz) and the general formula [Cu(L)Br2] (in which L=dbz, tbz or qbz) have been determined, together with the X-ray structure of two of the three compounds. Each compound has a tetrahedrally based CuN2Br2 chromophore with Cu–N distances from 1.976(3) to 1.993(11) Å and Cu–Br distances from 2.356(2) to 2.3982(7) Å. Angles N–Cu–N and Br–Cu–Br vary from 94.44(13) to 105.5(4)° and from 97.88(2) to 98.94(8)°, respectively. The length of the alkane chain determines the degree of tetragonality and the EPR measurements at 77 K as a frozen solution reveal a dx2−y2 for the copper compounds with the ligands dbz and qbz and a dz2 ground state with the copper tbz compound. The dihedral angles are 52.6(3) and 67.8(4)° for compounds [CuBr2(dbz)] and [CuBr2(tbz)], respectively.