Bonding properties of copper(II)-imidazole chromophores: structures and electronic properties of tetrakis imidazole copper(II) complexes. Molecular structures of Cu(N-methylimidazole)4(ClO4)2 and [Cu(N-methylimidazole)4(H2O)]Cl2(H2O)

Article abstract of DOI:10.1016/0277-5387(95)00111-5

The crystal and molecular structures of [Cu(NMIm)4(ClO4)2] (1) and [Cu(NMIm)4(H2O)2]Cl2.(H2O) (2) (NMIm=N-methylimidazole) have been determined from three-dimensional X-ray diffraction data. The structure of 1 consists of discrete centrosymmetric [Cu(NMIm)4(ClO4)2] units having a CuN4 plane with a set of two trans N-methylimidazole ligands nearly perpendicular to the CuN4 plane (dihedral angle 87.8°) and another set approximately parallel (dihedral angle 4.4°), and two perchlorates on the long z-axis with Cu-O length of 2.718(13) ?. The structure of 2 comprises two discrete structurally similar centrosymmetric [Cu(NMIm)4(H2O)2] cations interconnected with Cl(-) ions and hydrate molecules by hydrogen bonds. The dihedral angles between the imidazole and the CuN4 planes are 98.8° and 57.6° for one unit and 97.0° and 50.6° for another. Electronic and EPR spectra are reported for 1 and 2 and also for tetrakis complexes of imidazole, 4-methylimidazole, 4-phenylimidazole and benzimidazole. Analysis of the electronic spectra of 1 and 2 reveals that the former has D(2h) symmetry with non-degenerated(xz) and d(yz) orbitals, and the latter has D94h) symmetry with degene rate d(xz) and d(yz). This is ascribed to the difference in donor abilities of the axial ClO4(-) and H2O ligands. In solution, all tetrakis species exhibit different structures depending on the donor abilities of thesolvent molecules.