Crystal structures, spectral and magnetic properties of (μ-hydroxo)(μ-acetato)dicopper(II) complexes containing chelating amines

Abstract

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]₂1. 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]₂2a and [Cu₂(OH)(O₂CMe)(H₂O)₂(dmen)₂][ClO₄]₂2b, 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(μ-OH)(μ-O₂CMe)]²⁺ core. The co-ordination 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-O-Cu angles in 1, 2a and 2b are 3.339(2), 3.368(3), 3.395(7)Å, 120.1(2), 116.4(1) and 123.6(2)°, respectively. Complex 1 exhibits an axial ESR spectrum in a methanol glass giving g_∥= 2.26 (A_∥=164 × 10⁻⁴ cm⁻¹) and g_∥=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_∥= 2.25, A_∥=165 × 10^-4 cm^-1; g_∥=2.03) and 2b(g_∥=2.19, A_∥=184 × 10⁻⁴ cm⁻¹; g_∥= 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=−10.1 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.