Synthesis, structure, and magnetism of binuclear copper(II) complexes of pyrazole ligands with nitrogen-containing chelating arms. First example of di-µ-pyrazolato-dicopper(II,II) complexes

Abstract

The preparation of new dinucleating pyrazole ligands, 3,5-bis[(2-diethylamino)ethylaminomethyl]pyrazole (HL¹) and 3,5-bis[(3-dimethylamino)propylaminomethyl]pyrazole (HL²), has been accomplished. They afford binuclear copper(II) complexes of the formula [Cu₂L₂][BPh₄]₂(L = L¹ or L²). The structure of [Cu₂L¹₂][BPh₄]₂ was determined by single-crystal X-ray analysis. It crystallizes in the triclinic space group P with a= 13.437(4), b= 15.192(5), c= 12.364(4)Å, α= 116.38(3), β= 113.71(3), γ= 60.48(2)°, and Z= 1. The complex has a binuclear structure doubly bridged by the pyrazolate groups with the Cu ⋯ Cu separation 3.903(2)Å. The configuration geometry of each copper is a square pyramid, whose basal plane is formed by the two pyrazolate nitrogens and the ‘articular’ nitrogens [Cu–N 1.906(3)–2.028(3)Å] and the apical site by one of the ‘terminal’ nitrogens [Cu–N 2.496(5)Å]. The other terminal nitrogen is free from co-ordination. Cryomagnetic investigations over the temperature range 100–300 K revealed a strong antiferromagnetic spin exchange in both complexes. The exchange integral (J) based on the Heisenberg model, was evaluated as – 214 cm^–1 for [Cu₂L¹₂][BPh₄]₂ and –181 cm^–1 for [Cu₂L²₂][BPh₄]₂.