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

Abstract

The copper(II) p-chlorobenzoates [Cu 2R 4·CH 3OH·2H 2O] (I) and [Cu 2R 4·CH 3COCH 3·2H 2O] (II) dimeric complexes, where R=( p-ClC 6H 4CO 2), 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 -COO group arises from the appearance in the IR spectra of studied complexes of the stretching vibration ν(Cu–O) at 475 cm −1 and the combination frequencies ν(Cu–O)+ δ ring at 690 cm −1, ν(Cu–O)+ δ(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 coupled Cu(II) ions with short Cu–Cu distance (∼2.64 Å). The 77 K spectra indicate the coexistence of monomeric and dimeric species. The complex (I) presents two monomeric magnetic nonequivalent species, one (I′) with square-planar local symmetry D 4h (g ∥=2.301, g ⊥=2.067, A ∥=174×10 −4 cm −1, A ⊥=21.4×10 −4 cm −1) and the other (I″) with tetragonal–octahedral O h distorted symmetry due to the coordination of two water molecules along the Oz axis of Cu 2+ ion (g ∥=2.327, g ⊥=2.046, A ∥=162×10 −4 cm −1, A ⊥=43×10 −4 cm −1). Only the tetragonal–octahedral distorted species ( g ∥=2.324, g ⊥=2.044, A ∥=165×10 −4 cm −1, A ⊥=43×10 −4cm −1) occurs in the complex (II).