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

Monomeric and Dimeric Copper(II) Complexes of a Pyrrole‐Containing Tridentate Schiff‐Base Ligand

“…These are closely related to the pyridine-pyridine ligands, L A , L B and L C ( Figure 1) which have been well studied, [1] and summarised in our recent publication. [2] As seen from that summary, the complexes of the ligands L A , L B and L C , together with those obtained with other closely related tridentate Schiff-base ligands, [3,4] indicate that the use of less flexible tridentate ligands tends to result in the formation of monomeric and dimeric complexes while the use of more flexible tridentate ligands tends to give rise to dimeric or polymeric complexes. These dimeric and polymeric complexes can exhibit interesting magnetic behaviour.…”

“…[8] The order of addition used for the preparation of [CuL 1 Cl] (1) was modified to ensure that analytically pure olive green solid [CuL 1 Br] n (2) precipitated from that reaction solution. As was seen for the preparation of [Cu 2 (L 2 ) 2 -(µ-Br) 2 ] (7), [2] the ethylene-linked analogue, the wrong order of addition leads to a crude product contaminated by impurities involving the brominated-ligand, and this appeared to also be an issue with the methylene-linked ligand.…”

“…[2] Crystal structures of the complexes 6-8 and 10 indicate that use of the ethylene-linked ligand (L 2 ) -and its brominated form (L 2a ) -leads to the formation of dimeric or 1D-chain polymeric copper(II) complexes. Weak antiferromagnetic exchange is observed for complexes 6-8 and 10.…”

“…[2] Here, we detail the synthesis, spectral and structural characterisation of the copper(II) complexes of (L 1 The ligand HL 1 , a homologue of HL 2 , is also potentially a tridentate Schiff-base ligand containing both a pyridine and a pyrrole moiety. As seen for HL 2 , the pyrrole NH moiety in HL 1 can be deprotonated in the presence of a base and this leads to tridentate coordination of (L 1 ) -to the metal ion.…”

“…[Cu 2 (L 1 ) 2 (µ 1,3 -NCS) 2 ]. The structure determinations on 4 and 5 showed that in both cases the copper(II) ion is in a distorted square-planar N 2 X 2 environment, with the pyrrole NH remaining non-deprotonated and uncoordinated.…”