Valence directed binding mode of [2 × 2] iron grids of an unsymmetrical picolinic hydrazone based ligand

Abstract

A new unsymmetrical ditopic ligand H₂L was used to synthesize two [2 × 2] grid type tetranuclear trivalent and mixed-valent Fe^III₄, Fe^II₂Fe^III₂ complexes, respectively. Both complexes [Fe^III₄(L′)₄] (1) and [Fe^II₂Fe^III₂(L)₄](BF₄)₂·2CH₃CN (2) have been X-ray structurally characterized. The magnetic properties of complexes 1 and 2 show dominant antiferromagnetic coupling. Mössbauer studies were carried out to confirm the electronic states of the iron centres. The structural properties of the two complexes are diverse though they have been synthesized from the same ligand but under different conditions. In 1, all the Fe(III) metal centres are coordinated by two pairs of parallel but oppositely aligned ligand strands arranged in a ‘head-to-tail’ fashion, whereas in 2, Fe(II) and Fe(III) metal centres are coordinated by two pairs of parallel aligned ligand strands arranged in a ‘head-to-head’ fashion.