Synthesis, crystal structure and magnetic properties of di-µ-hydroxo-bis[(2,2′-bipyridine)(trifluoromethanesulfonato-O)-copper(II)]

Abstract

The compound [Cu₂(bipy)₂(OH)₂(CF₃SO₃)₂](bipy = 2,2′-bipyridine) has been synthesised and its crystal structure determined by X-ray crystallographic methods. Crystals are triclinic with a= 8.165(2), b= 14.265(2), c= 18.748(5)Å, α= 93.10(1), β= 100.58(2), γ= 99.17(1)°, space group P, and Z= 3. Least-squares refinement of 5872 reflections with I 3σ(I) and 679 parameters gave a final R′= 0.042. The structure consists of discrete centrosymmetric and non-centrosymmetric di-µ-hydroxo-copper(II) dimers with 2,2′-bipyridine as outer ligand and semi-co-ordinated CF₃SO₃^– anions. Intramolecular copper–copper distances are 2.920(1) and 2.8917(7)Å for the centrosymmetric and non-centrosymmetric dimers respectively. The co-ordination geometry around each copper ion is square pyramidal with the bridging hydroxo groups and two nitrogen atoms of the bipyridine ligand comprising the basal plane, and the apical site occupied by an oxygen atom of the CF₃SO₃^– group. Coupled variable-temperature powder ESR spectral and magnetic susceptibility data demonstrate that the copper(II) ions within both dimeric molecules are ferromagnetically coupled (J_c= 17, J_a= 158 cm^–1, g 2.09 and 2.10, with J= singlet–triplet energy gap and subscripts c and a denoting the centrosymmetric and asymmetric dimers). The nature and strength of the exchange interaction is discussed on the basis of the structural features and correlated with previously reported magnetostructural data for other di-µ-hydroxo-bis[2,2′-bipyridine)copper(II)] complexes.