IR and ESR studies on some dimeric copper(II) complexes

The copper(II) p-chlorobenzoates [Cu2R4CH3OH.2H(2)O] (I) and [Cu2R4.CH3COCH 3.2H(2)O] (II) dimeric complexes, where R = (p-ClC6H4CO2), as well as their monomeric species which occur at 77 K have been investigated by IR and ESR spectroscopy. The coordination of the copper(II) ions at the carboxylic -C OO group arises from the appearance in the IR spectra of studied complexes of the stretching vibration v(Cu-O) at 475 cm(-1) and the combination frequ encies v(Cu-O) + delta (ring) at 690 cm(-1) v(Cu-O) + delta (O-C=O) at 770- 800 cm(-1). The room temperature powder ESR spectra of the both copper(II) complexes correspond to a randomly oriented triplet state (S = 1) for coupl ed Cu(II) ions with short Cu-Cu distance (similar to2.64 Angstrom). The 77 K spectra indicate the coexistence of monomeric and dimeric species. The co mplex (I) presents two monomeric magnetic nonequivalent species. one (I') w ith square-planar local symmetry D-4h (g(parallel to) = 2.301, g(perpendicu lar to) = 2.067, A(parallel to) = 174 x 10(-4) cm(-1), A(perpendicular to) = 21.4 x 10(-4) cm(-1)) and the other (I") with terragonal-octahedral O-h d istorted symmetry due to the coordination of two water molecules along the Oz axis of Cu2+ ion (g(parallel to) = 2.327, g(perpendicular to) = 2.046, A (parallel to) = 162 X 10(-4) cm(-1). A(perpendicular to) = 43 x 10(-4) cm(- 1)). Only the tetragonal-octahedral distorted species (g(parallel to) = 2.3 24, g(perpendicular to) = 2.044, A(parallel to) = 165 x 10(-4) cm(-1), A(pe rpendicular to) = 43 X 10(-4)cm(-1)) occurs in the complex (II). (C) 2001 E lsevier Science B.V. All rights reserved.