A one-dimensional assembly of a square-planar copper(ii) complex with alternating short and long Cu⋯Cu distances. Metal ion spin-exchange via π-π interactions

Abstract

A mixed-ligand copper(II) complex, [Cu(bhac)(Hdmpz)], with a tridentate Schiff base, acetylacetone benzoylhydrazone (H₂bhac) and a monodentate heterocycle, 3,5-dimethylpyrazole (Hdmpz), has been synthesized and characterized by analytical, infrared and electronic absorption spectroscopy, and cyclic voltammetry. The molecular structure of the complex has been determined by X-ray crystallography. The metal ion is coordinated to the enolate-O, the imine-N and the deprotonated amide-O centres of the deprotonated Schiff base (bhac²⁻) and to the sp² N atom of Hdmpz. The coordination geometry around the metal centre is square-planar. There is no displacement of the metal centre from the N₂O₂ square plane. The whole molecule is essentially planar, barring a small variation in the orientation of the Hdmpz plane with respect to the {Cu(bhac)} plane. In the solid state, two types of π-π interactions on two sides of [Cu(bhac)(Hdmpz)] molecule lead to a one-dimensional arrangement of the complex with sequential short [3.5952(8) Å] and long ([5.5960(12) Å] Cu⋯Cu distances. Solid state as well as frozen solution EPR spectral measurements reveal an antiferromagnetically coupled dicopper(II) system and indicate a magnetic exchange interaction mediated by π-π interactions. Magnetic susceptibility data in the temperature range of 10–300 K are consistent with this observation. The magnitude of the coupling constant J, obtained by least-squares fitting of the data using the Bleany–Bowers expression, is −6.0(1) cm⁻¹.