CRYSTAL-STRUCTURES, SPECTRAL AND MAGNETIC-PROPERTIES OF (MU-HYDROXO)(MU-ACETATO)DICOPPER(II) COMPLEXES CONTAINING CHELATING AMINES

The reaction of Cu2(O2CMe)4(H2O)2! with N,N,N',N'-tetramethylethane-1 ,2-diamine (tmen) in ethanol yielded the dicopper(II) complex Cu2(OH) (O2CMe)(tmen)2!ClO4!2 1. A similar reaction with N,N-dimethylethane-1 ,2-diamine (dmen) afforded a crystalline product 2 in which two dicopp er(II) complexes, Cu2(OH) (O2CMe) (dmen)2! ClO4!2 2a and CU2(OH) (O 2CMe) (H2O)2(dmen)2! ClO4!2 2b, are cocrystallized in a 1:1 molar rat io along with 2NaClO4. The crystal structures of 1 and 2 have been det ermined. The complexes have an asymmetrically dibridged CU2(mu-OH)(mu -O2CMe)!2+ core. The coordination geometry of the metal is square plan ar (CuO2N2) . The copper atoms in 2b have a square-pyramidal CuO3N2 co -ordination sphere. The Cu ... Cu distances and Cu-0-Cu angles in 1, 2 a and 2b are 3.339(2), 3.368(3), 3.395(7) angstrom, 120.1(2), 116.4(l) and 123.6(2)-degrees, respectively. Complex 1 exhibits an axial ESR s pectrum in a methanol glass giving g(parallel-to) = 2.26 (A(parallel-t o) = 164 x 10(-4) CM-1) and g(parallel-to) = 2.04. The ESR spectra obt ained from the bulk material of the dmen product are indicative of the presence of two dimers, viz. complex 2a (g(parallel-to) = 2.25, A(par allel-to) = 165 x 10(-4) cm 1; g(perpendicular-to) = 2.03) and 2b (g(p arallel-to) = 2.19, All = 184 X 10(-4) cm-1; g(perpendicular-to) = 2.0 ). Variable-temperature magnetic susceptibility measurements on these complexes show an intramolecular antiferromagnetic coupling in the dim eric core. The fitting parameters are J = -27.8 cm-1, g = 2.1 for comp lex 1 and J = -1 0. 1 cm-1, g = 2.0 for 2. The magnetostructural prope rties of the complexes are discussed. There is a linear correlation of the -2J values with the Cu ... Cu distances among dibridged complexes having square-planar copper(II) centres.