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.