X-Ray crystal structures and magnetic properties of azide-bridged binuclear copper(II) complexes containing the Schiff-base ligand derived from 2-pyridinecarbaldehyde and histamine. Structure–magnetism relationship

Abstract

The structures of the complexes [Cu₂(L¹)₂(N₃)₂][ClO₄]₂(1){ L¹= 1-(imidazol-4-yl)-2-[(2-pyridylmethylene)amino]ethane} and [Cu₂(L¹)₂(N₃)₃]Cl·2H₂O (2) have been determined by X-ray methods. Complex (1) contains discrete [Cu₂(L¹)₂(N₃)₂]²⁺ cations which are located at centres of inversion. The geometry around each copper(II) ion is square pyramidal. The two basal planes in the complex cation are parallel and separated by 2.64 Å. The two azide ions which are parallel to each other bridge in an end-on fashion between a basal position of one square pyramid and an apical position of the other. Magnetic susceptibility data for (1) show a ferromagnetic interaction (Weiss constant θ=+23 K) above 200 K. On the other hand, below 200 K, it is considered that there is a weaker exchange interaction than that above 200 K. In differential scanning calorimetry curves for (1), small thermal anomalies have been observed over the temperature range 150–250 K. Complex (2) contains an azide-bridged, centrosymmetric copper(II) dimeric cation. The five-coordinate geometry around each copper(II) ion is square pyramidal. An azide ion bridges in an endto-end fashion between the two apical positions of two square pyramids. A very weak antiferromagnetic exchange interaction is found for (2)(0 J–0.5 cm^–1, where J denotes the exchange integral defined by the Hamiltonian ℋ=–2JS₁S₂).