Magnetic exchange in some polynuclear bis(azole)dihalogenocopper(II) complexes

Abstract

Variable-temperature (4.2–80.0 K) magnetic-susceptibility data are reported for compounds CuX₂L₂[X = Cl or Br; L = imidazole (imH), N-methylimidazole (mim), pyrazole (Hpz), and indazole (Hindi)]. The magnetic data have been analysed with five different equations, i.e. the Heisenberg polynomial, the lsing expression, the parallel component of the lsing expression, the Monte-Carlo calculation of Jotham, and the dimeric Bleaney–Bowers expression. Ligand-field and e.s.r. spectra (X- and Q-band) are also presented. The magnetic properties of none of the compounds can be described with the lsing model of anisotropic coupling. For the compounds CuBr₂L₂(L = Hpz or Hind) excellent fits are obtained with the Heisenberg model of isotropic coupling, yielding J=–19.0 cm^–1 and g 2.06, and J=–18.7 cm^–1 and g 2.06 respectively. For CuCl₂L₂(L = imH or mim) and CuBr₂(mim)₂ the Jotham expression gives the best results, with J=–5.36 cm^–1 and g 2.19, J=–2.88 cm^–1 and g 2.36, and J=–11.7 cm^–1 and g 2.15 respectively. The magnetism of CuCl₂(Hpz)₂ can best be described with the dimeric Bleaney–Bowers expression (J=–1.3 cm^–1 and g 2.18). In CuCl₂(Hind)₂ the copper(II) ions appear to be coupled ferromagnetically. Unfortunately no unique fit has been obtained; both the parallel lsing and Bleaney–Bowers expressions fit the data (J= 0.9 cm^–1 and g 2.21, and J= 5.2 cm^–1 and g 2.10 respectively).