Bifunctional Fe(ii) spin crossover-complexes based on ω-(1H-tetrazol-1-yl) carboxylic acids

Abstract

To increase the supramolecular cooperativity in Fe(II) spin crossover materials based on N1-substituted tetrazoles, a series of ω-(1H-tetrazol-1-yl) carboxylic acids with chain-lengths of C₂–C₄ were synthesized. Structural characterization confirmed the formation of a strong hydrogen-bond network, responsible for enhanced cooperativity in the materials and thus largely complete spin-state transitions for the ligands with chain lenghts of C₂ and C₄. To complement the structural and magnetic investigation, electronic spectroscopy was used to investigate the spin-state transition. An initial attempt to utilize the bifunctional coordination ability of the ω-(1H-tetrazol-1-yl) carboxylic acids for preparation of mixed-metallic 3d–4f coordination polymers resulted in a novel one-dimensional gadolinium-oxo chain system with the ω-(1H-tetrazol-1-yl) carboxylic acid acting as μ₂-η²:η¹ chelating–bridging ligand.