Synthesis, characterization and structures of copper(II) complexes with amide-based ligands: Unusual formation of a linear trimer and a zig-zag chain and their contrast magnetic behaviour

Abstract

The present work illustrates the versatile coordination modes of the amide-based ligands towards copper(II) ion. The reaction of the deprotonated form of the ligand, [L 1] 2− with CuCl 2 affords a linear trinuclear complex, [Cu 3(L 1) 2(Cl) 2(H 2O)] ( 1) which has been characterized thoroughly including single crystal structure analysis. The structure of 1 shows that one of the arm of the flexible ligand flips to coordinate second copper(II) centre, resulting in the formation of a trinuclear complex. On the other hand, ligand H 2L 2 in its deprotonated form reacts with Cu(II) ion to give complex 2 with general formula, [Cu(L 2)] n ( 2). The crystal structure of the complex 2 shows that each copper is square-pyramidal with 5th coordination coming from the O-atom of the amide group from a neighbouring complex. This results in the generation of an one-dimensional zig-zag chain. The variable temperature magnetic measurements of the complexes, 1 and 2 show that while Cu ions in the former are antiferromagnetically coupled ( J = −110.34 cm −1), a weak ferromagnetic interaction ( J = +3.08 cm −1) exists in the later. A rationale, based on the orbital overlap from the copper ions and associated ligands, is provided for the observed magnetic coupling between the copper ions.