An iron(II) spin crossover grafted cyclotriphosphazene

Article abstract of DOI:10.1016/j.poly.2013.02.065

The synthesis of the new cyclotriphosphazene (CTP) ligand substituted with a pendant 2,6-bis(benzimidazole-2-yl)pyridine (bbp), namely (pentaphenoxy)[4-{2, 6-bis(benzimidazole-2-yl)pyridine-4-yl}phenoxy]cyclotriphosphazene L is reported. The single crystal structure of L shows that the bbp group is attached to the CTP via the oxygen. L reacts with FeX₂ (X = ClO ₄^- or BF₄^-) salts forming the [FeL₂]X₂ complexes 1 and 2 respectively. For [FeL ₂](BF₄)₂ (2), the single crystal structure shows an 'N₆' coordination sphere around the iron atom. UV-Vis, resonance Raman and M?ssbauer spectroscopies and magnetic susceptibility measurements, aided by density functional theory (DFT) calculations, determine the complexes are low spin below 300 K but display spin crossover (SCO) behavior above this temperature, hence showing that the addition of a phosphazene to a SCO moiety does not prevent SCO.