Co-ordination chemistry of mixed pyridine–phenol and phenanthroline–phenol ligands; a variable-temperature electron paramagnetic resonance and magnetic susceptibility study on two binuclear copper(II) complexes with Cu2(µ-O)2(µ-1,3,-O2CMe) cores

Abstract

The EPR spectra (characteristic of triplet species) of the complexes [Cu₂L¹₂(µ-1,3-O₂CMe)][PF₆]1[HL¹= 6-(2-hydroxyphenyl)-2,2′-bipyridine] and [Cu₂L²₂(µ-1,3-O₂CMe)][PF₆]2[HL²= 2-(2-hydroxyphenyl)-1,10-phenanthroline], previously structurally characterised as containing Cu₂(µ-O)₂ cores in which the phenolate oxygen atoms of L¹ and L² bridge both copper(II) centres, have been successfully modelled using a perturbation-theory approach. The Cu ⋯ Cu distances calculated from the spectra are in reasonable agreement with the values given by the crystal structures. By measuring the variation in intensity of the spectrum of 1 with temperature it was established that 1 is antiferromagnetic with J= 52 ± 8 cm^–1. Variable-temperature magnetic susceptibility measurements on 1 and 2 confirm the presence of moderate antiferromagnetic couplings, although the presence of a mononuclear impurity in each case precludes use of the Bleaney–Bowers equation to obtain more accurate values of J.