Synthesis, crystal structure and hydrolysis of a dinuclear copper(II) complex constructed by N₂O donor Schiff base and 4,4′-bipyridine: discrete supra-molecular ensembles vs. oligomers

Abstract

The tridentate Schiff base ligand, 7-amino-4-methyl-5-aza-3-hepten-2-one (HAMAH), prepared by the mono-condensation of 1,2-diaminoethane and acetylacetone, reacts with Cu(BF₄)₂ • 6H₂O to produce initially a dinuclear Cu(II) complex, [{Cu(AMAH)} ₂ (μ-4,4′-bipy)](BF₄)₂ (1) which undergoes hydrolysis in the reaction mixture and finally produces a linear polymeric chain compound, [Cu(acac) ₂(μ-4,4′-bipy)]_n (2). The geometry around the copper atom in compound 1 is distorted square planar while that in compound 2 is essentially an elongated octahedron. On the other hand, the ligand HAMAH reacts with Cu(ClO₄)₂ • 6H₂O to yield a polymeric zigzag chain, [{Cu(acac)(CH₃OH)(μ-4,4′-bipy)}(ClO₄)]_n (3). The geometry of the copper atom in 3 is square pyramidal with the two bipyridine molecules in the cis equatorial positions. All three complexes have been characterized by elemental analysis, IR and UV–vis spectroscopy and single crystal X-ray diffraction studies. A probable explanation for the different size and shape of the reported polynuclear complexes formed by copper (II) and 4,4′-bipyridine has been put forward by taking into account the denticity and crystal field strength of the blocking ligand as well as the Jahn–Teller effect in copper (II).