Croconato-bridged copper(ii) complexes: synthesis, structure and magnetic characterization

Abstract

Three croconato-bridged Cu(II) complexes were synthesized and structurally characterized including dinuclear [Cu₂(Et₄dien)₂(μ_1,2,3,4-C₅O₅)](ClO₄)₂·3H₂O (1) and [Cu₂(pmap)₂(μ_1,2,3,4-C₅O₅)](ClO₄)₂·2H₂O (2) and the 1D coordination polymer {[Cu(dmpzp)(μ_1,2,3,4-C₅O₅)]·H₂O}_n (3), where Et₄dien = N,N′,N′′,N′′-tetraethylethylenetriamine, pmap = bis(2-(2-pyridyl)ethyl)-(2-pyridylmethyl)amine and dmpzp = 1-(2-methylpyridyl)-3,5-dimethyl-1-H-pyrazole. The synthesized complexes were further characterized by a single crystal X-ray analysis which revealed the bis-bidentate chelating nature of the μ_1,2,3,4-croconato ligand with the intra-dimer Cu⋯Cu bond distances ranging from 6.79 to 7.69 Å across the bridged croconate. The magnetic susceptibility measurements at varying temperatures (1.9–300 K) showed that the complexes exhibit a weak antiferromagnetic (AF) coupling with J values = −2.67 cm⁻¹ for 1 and 2, and −4.05 cm⁻¹ for 3. The weak AF coupling was also predicted based on the DFT calculations. The magnetic properties of the complexes are discussed in light of their structures and compared with the previously reported croconato-bridged Cu(II) complexes.