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 dicopper(II) complexes, [Cu2(OH) (O2CMe) (dmen)2] [ClO4]2 2a and [CU2(OH) (O2CMe) (H2O)2(dmen)2] [ClO4]2 2b, are cocrystallized in a 1:1 molar ratio along with 2NaClO4. The crystal structures of 1 and 2 have been determined. The complexes have an asymmetrically dibridged [CU2(mu-OH)(mu-O2CMe)]2+ core. The coordination geometry of the metal is square planar (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, 2a 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 spectrum in a methanol glass giving g(parallel-to) = 2.26 (A(parallel-to) = 164 x 10(-4) CM-1) and g(parallel-to) = 2.04. The ESR spectra obtained 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(parallel-to) = 165 x 10(-4) cm 1; g(perpendicular-to) = 2.03) and 2b (g(parallel-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 dimeric core. The fitting parameters are J = -27.8 cm-1, g = 2.1 for complex 1 and J = -1 0. 1 cm-1, g = 2.0 for 2. The magnetostructural properties 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.