Monomeric, dimeric and 1D chain polymeric copper(ii) complexes of a pyrrole-containing tridentate Schiff-base ligand and its 4-brominated analogue

Abstract

The synthesis and characterisation of the Schiff-base ligand, HL¹ [N-(1H-pyrrol-2-ylmethylene)-2-pyridineethanamine; derived from 2-formylpyrrole and 2-(2-aminoethyl)pyridine] and copper(II) complexes of (L¹)⁻ in the form of [Cu₂(L¹)₂(μ-X)₂] (X = Cl⁻, 1; X = Br⁻, 2; X = N₃⁻, 3; X = NCS⁻, 4) are reported. Bromination of the β position on the pyrrole ring of (L¹)⁻ was observed in the preparation of the di(μ-bromo)-bridged complex [Cu₂(L¹)₂(μ-Br)₂] (2), and the copper(II) complex of the brominated pyrrole derivative (L^1a)⁻, 5, was also obtained. Procedures to synthesise analytically pure samples of 2 and 5 were developed. X-Ray structure determinations carried out on 1, 2, 3 and 5 reveal that 1, 2 and 3 are all doubly-bridged square pyramidal copper(II) dimers [Cu₂(L¹)₂(μ-X)₂] while 5 is an unusual mono(μ-bromo)-bridged square pyramidal copper(II) 1D chain polymer of the brominated ligand (L^1a)⁻, [Cu(L^1a)(μ-Br)]_∞. In the case of [Cu₂(L¹)₂(μ-N₃)₂] (3) the structure determination reveals that the azide groups bridge the two copper(II) ions in a 1,1-N₃, end-on, fashion. Variable temperature magnetic susceptibility measurements carried out on the structurally characterised dimeric and polymeric copper(II) complexes 1, 2, 3 and 5, revealed weak antiferromagnetic exchange.