BONDING PROPERTIES OF PENTACOORDINATE CU(II)-N CHROMOPHORES - STRUCTURES AND ELECTRONIC-SPECTRA OF COPPER(II) COMPLEXES OF TRIS(2-AMINOETHYL)AMINE (TREN) - MOLECULAR-STRUCTURES OF [CU(TREN)(N-ACETYLHISTAMINE)](CLO4)2 AND [CU(TREN)(2-METHYLIMIDAZOLE)](CLO4)2

Tris(2-aminoethyl)aminecopper(II) perchlorate complexes, [Cu(tren)L](ClO4)2 [tren is tris(2-aminoethyl)amine and L are neutral N-donor ligands including imidazoles, pyridines and amines], have been synthesized and characterized. The X-ray crystal structures of [Cu(tren)(achmH)](ClO4)2 (1) and [Cu(tren)(2MImH)](ClO4)2 (2) (achmH = N-acetylhistamine; 2MImH = 2-methylimidazole) have been determined. Their structures consist of discrete perchlorate anions and distorted trigonal-bipyramidal [Cu(tren)(N-donor)]2+ cations with the three primary amine groups of the tren ligand forming the equatorial plane, where one of the equatorial angles is larger than the other two and the Cu-N bond opposite the largest equatorial N-Cu-N angle is significantly longer than the other two. Electronic and EPR spectra are reported for these complexes. The LF spectra are analysed in trigonal-bipyramidal symmetry with the Jahn-Teller effect being considered in the excited state and the effect of geometric distortions. The d-orbitals are assigned in a sequence of d(z)2 m much greater than d(x2-y2) > d(xy) > d(xz) approximately d(yz). The bonding properties of the CuN5 chromophores are elucidated and discussed with reference to the electronic structures of the complexes, suggesting no pi-interaction in the axial Cu-N bonds.