A strongly hydrogen-bonded one-dimensional high-spin dinuclear Fe(ii) complex

Abstract

In this study, we report the synthesis and detailed characterization of a novel chain compound, composed of hydrogen-bonded dinuclear complexes, in which two Fe(II) ions are bridged by a 2,2′-biimidazolate (bim²⁻) dianion. The crystal structure of [(tpma)Fe(μ-bim)Fe(Hbim)₂] (1), where tpma = tris(2-pyridylmethyl)amine, exhibits a 1D zigzag chain architecture, formed through double hydrogen bonds between terminal 1H-2,2′-biimidazolate monoanions (Hbim⁻), with an N⋯H distance of 1.72 Å. Magnetic susceptibility measurements reveal weak antiferromagnetic coupling between the Fe(II) centers with the exchange constant J = −1.4 cm⁻¹, mediated by the bridging ligand. The directional hydrogen bonding network, combined with π–π and H–π intermolecular interactions, suggests potential for proton dynamics that could lead to ferroelectric behavior. This complex represents the first example of a bim²⁻ ligand bridging two iron ions and the first dimeric complex containing both bim²⁻ and Hbim⁻ ligands, which form strong one-dimensional hydrogen bonds. Investigation of ferroelectric behavior and potential interplay between functional properties are ongoing.