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)A, 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)A. 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)A] and the apical site by one of the ‘terminal’ nitrogens [Cu–N 2.496(5)A]. 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.