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](C lO4)2 [tren is tris(2-aminoethyl)amine and L are neutral N-donor ligan ds including imidazoles, pyridines and amines], have been synthesized and characterized. The X-ray crystal structures of [Cu(tren)(achmH)](C lO4)2 (1) and [Cu(tren)(2MImH)](ClO4)2 (2) (achmH = N-acetylhistamine; 2MImH = 2-methylimidazole) have been determined. Their structures con sist 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 equator ial 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 othe r two. Electronic and EPR spectra are reported for these complexes. Th e LF spectra are analysed in trigonal-bipyramidal symmetry with the Ja hn-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.