BONDING PROPERTIES OF CU(II)-N CHROMOPHORES: PREPARATION, STRUCTURE, AND SPECTROSCOPIC PROPERTIES OF N,N,N′,N′-TETRAMETHYLETHYLENEDIAMINE COPPER (II) COMPLEXES. MOLECULAR STRUCTURE OF BIS(4-METHYLPYRIDINE)PERCHLORATO-(N,N,N′,N′-TETRAMETHYLETHYLENEDIAMINE) COPPER(II) PERCHLORATE

Abstract

Abstract N,N,N′,N′-Tetramethylethylenediamine (tmen) copper(II) perchlorate and/or tetrafluoroborate complexes of the type Cu(tmen)L2(anion)2, where L represents imidazole, N-methylimidazole, 2-methylimidazole, 4-methylimidazole, 4-methylpyridine and NH3, have been synthesized and characterized by analysis, and electronic, vibrational and epr spectroscopic measurements. The molecular structure of [Cu(tmen)(4Mpy)2(ClO4)](ClO4) (4Mpy = 4-methylpyridine) has been determined using three-dimensional X-ray diffraction data. The complex salt is monoclinic, space group P21/n with Z = 4, a = 11.876(3), b = 13.548(2), c = 15.773(3)Å and β = 95.47(2)°. Least-squares refinement of the structure yielded R = 7.48% and Rw = 7.29% for 1164 independent reflections at 297K. The Cu(II) ion is five coordinated (square pyramid) with the tmen and the 4-methylpyridine ligands on the basal plane, mean Cu-N(tmen) 2.074 Å and mean Cu-N(4Mpy) distances 2.008 Å, and one ClO4 − at the apex, Cu-O 2.353(14) Å. Both 4-methylpyridine planes are nearly perpendicular to the CuN4 coordination plane; dihedral angles are 92.5° and 98.0°. Based on spectroscopic data, similar structures are proposed for other tmen complexes. The bonding properties of the heterocyclic ligands to the tmen-Cu(II) core are elucidated and discussed by reference to the electronic structures of the complexes deduced from Gaussian analyses of their LF spectra.