Synthesis and characterization of iron(II) complex with unsymmetrical heterocyclic (2-pyridyl)(4-imidazolyl)azine

A new iron(II) complex bearing unsymmetrical azine, [Fe(HLH)2](PF6)2·H2O·MeCN (HLH = 2-pyridylmethylidenehydrazono(4-imidazolyl)methane), was synthesized exclusively by a reaction of 2-pyridine carboxaldehyde, 1H-imidazole-4-carboxaldehyde, hydrazine monohydrate and FeCl2·4H2O (in a molar ratio of 2:2:2:1) in methanol, followed by the addition of an aqueous NH4PF6 solution. It was characterized using spectroscopic techniques, elemental analysis, magnetic measurement, and cyclic voltammetry. The molecular and crystal structure of the compound was revealed by X-ray analysis, where an iron(II) ion was surrounded by two HLH azines with a planar E(py),Z(im) conformation, and tridentate κ3N,N’,N” coordination mode, forming a monomeric six-coordinated and diamagnetic complex. The complex cations were linked by water molecules via intermolecular hydrogen-bonding interactions between the imidazole N−H and the neighboring uncoordinated azine-N atom, forming a 1D chain structure. The selective formation of this unsymmetrical azine (HLH) from a stoichiometric mixture of the components would result from the steric preference of the five- and six-membered chelate rings by the 2-pyridyl and 4-imidazolyl azine moieties, respectively, with the E(py),Z(im) configuration.

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