Hetero triply-bridged dinuclear copper(ii) compounds with ferromagnetic coupling: a challenge for current density functionals

Abstract

Seven new hetero triply-bridged dinuclear Cu(II) compounds have been synthesized and characterized corresponding to a series with general formula [Cu₂(L)₂(μ-OH)(μ-OH₂)(μ-O₂CR)]X₂ (where L = bpy = 2,2′-bipyridine, 4,4′-dmbpy = 4,4′-dimethyl-2,2′-bipyridine and 5,5′-dmbpy = 5,5′-dimethyl-2,2′-bipyridine; R = H for formate, CH₃ for acetate, CH₂CH₃ for propionate and C(CH₃)₃ for trimethylacetate and X = CF₃SO₃⁻ and ClO₄⁻). All compounds exhibit ferromagnetic behavior with the experimental J values derived from magnetic susceptibility measurements being in the 73–104 cm⁻¹ range. The overall qualitative behavior is reproduced by state of the art density functional theory based methods. However, none of the functionals is able to reproduce the fine details along the series which constitutes an excellent benchmark for future developments.