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

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).

Graphical abstractThe 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). 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).Figure optionsDownload full-size imageDownload as PowerPoint slide