Crystal structures and magnetic properties of bi- and tetra-nuclear copper(II) complexes of 2,6-diformyl-4-methylphenol di(benzoylhydrazone)

Abstract

The crystal structures of the bi- and the tetra-nuclear copper(II) complexes [Cu₂L(OCH₃)]·dmf (1) and [{Cu₂L(OH)·dmf}₂](2) have been determined, where H₃L denotes 2,6-diformyl-4-methyl-phenol di(benzoylhydrazone). Complex (1) assumes a binuclear structure, in which two copper(II) ions are bridged by an endogenous phenolic oxygen atom of the dinucleating ligand L and an exogenous methoxide oxygen atom. Two molecules are stacked parallel in the crystal, where the shortest intermolecular Cu ⋯ Cu and Cu ⋯ O distances are 3.572(1) and 3.645(5)Å, respectively. Complex (2) assumes a tetranuclear structure composed of two binuclear units related by a centre of symmetry. Two copper(II) ions in the crystallographically unique binuclear unit are bridged by the endogenous phenolic oxygen atom and an exogenous hydroxide oxygen atom. The hydroxide oxygen further co-ordinates to an axial position of a copper(II) ion of an adjacent binuclear unit related by the centre of symmetry with a bond distance of 2.322(5)Å. Cryomagnetic data for complexes (1) and (2)(80–300 K) can be reproduced by an equation based on the Heisenberg model (H =–2JS₁S₂, S₁= S₂=½) with the parameters of J=–315 cm^–1 and g= 2.05 for (1) and J=–190 cm^–1 and g= 2.10 for (2) although in the case of (2) the interdimer distances of Cu(2)⋯ Cu(2^II)(1 –x, –y, 2 –z) and Cu(1)⋯ Cu(2^II) are only 3.186(1) and 3.282(1)Å respectively. The magnetism of complex (2) implies that the intradimer antiferromagnetic interaction through the endogenous phenolic oxygen is predominant, and the intra- and inter-dimer magnetic interactions through the exogenous hydroxide oxygen atom contribute little to the magnetic susceptibility, because the hydroxide oxygen atom is bound to four atoms (3Cu and H) and hence has no lone-pair electrons.