Racemic metal phosphonates based on 1-phosphonomethyl-2-benzimidazol-piperidine

Abstract

Based on racemic 1-phosphonomethyl-2-benzimidazol-piperidine (pbpH₂), three metal phosphonate compounds with the formula M(pbp)(H₂O)₂·3H₂O [M = Ni(1), Co(2)] and Cu(pbp)·2H₂O (3) have been synthesised and structurally determined. All of the compounds contain chiral chains, in which adjacent M(II) ions are linked solely by O–P–O bridges. In compounds 1 and 2, linear chains of the opposite handedness are fused by hydrogen bonds forming racemic double chains. The double chains are further connected by hydrogen bond interactions into a three-dimensional (3D) supramolecular network structure. In compound 3, helical chains with the opposite helicity are arranged alternately in the structure leading to a racemic 3D network. π–π stacking and hydrogen bond interactions are found to exist between the chains. Magnetic studies reveal that dominant antiferromagnetic interactions are propagated in 1–3 between the magnetic centers via the O–P–O pathways.