Crystal and molecular structure and magnetic properties of a tetrameric copper complex formed by the terdentate ligand N-2-pyridylsalicylaldimine

Abstract

The crystal and molecular structure of the tetranuclear complex tetrakis[(aquo)-(N-2-pyridylsalicylaldiminato)copper(II)] tetranitrate has been determined from counter-collected single-crystal X-ray diffraction data and refined to R 0·072 for 1570 independent reflections. Two complex cations, having crystallographically imposed D₂(222) point symmetry, occupy a tetragonal unit cell, space group P4₂2₁2, of dimensions: a= 14·83 and c= 13·58 Å. The four copper atoms in the tetranuclear cluster are situated in an almost square arrangement, the two independent copper–copper distances being 3·077(2) and 3·171(2)Å. The tridentate Schiff-base ligand is co-ordinated to three different copper atoms, the phenolic oxygen bridging two of the atoms, while the pyridine nitrogen atom is co-ordinated to the third. The water molecule occupies the axial position of a distorted square pyramidal co-ordination sphere about the copper atom, while the nitrate ion is not co-ordinated and appears to be statistically disordered between two sites in the crystal.

The magnetic susceptibility measured over the range 90—300 K indicates an antiferromagnetic coupling between the pairs of oxygen bridged copper atoms, with an interaction constant J/k of ca.–60 K. There appears to be little, if any, interaction between the two binuclear units making up the tetrameric complex ion.