Magnetostructural correlations for hexachlorodicuprate(II) salts: crystal structure and magnetic properties of the tetrameric complex [{Cu2(terpy)Cl4}2](terpy = 2,2′:6′,2″-terpyridine)

Abstract

The crystal structure of the complex [{Cu₂(terpy)Cl₄}₂](terpy = 2,2′:6′,2″-terpyridine) has been determined. It crystallizes in space group P, a= 11.136(7), b= 8.365(4), c= 9.263(5)Å, α= 97.13(5), β= 93.60(5), γ= 88.82(5)° and Z= 2. Least-squares refinement of 2 591 reflections with I > 3σ(I) and 218 parameters gave a final R= 0.070 and R′= 0.074. The structure consists of discrete neutral tetrameric units formed by slightly bifolded [Cu₂Cl₆]^2– dimers stacked between two planar [Cu(terpy)Cl]⁺ entities. The co-ordination geometry around each copper ion can be described as tetragonal square pyramidal. Temperature-dependent e.s.r. spectra and magnetic susceptibility measurements have been reinterpreted on the basis of the tetrameric nature of the compound. Exchange coupling parameters of J₁₂/K=–13 ± 1 K and J₂₃/k=–68 ± 2 K have been estimated. The strength of the exchange interaction in the [Cu₂Cl₆]^2– units is discussed on the basis of the structural features and compared with other bifolded systems, confirming the correlation of J with the bifold angle.