An iron(II) spin crossover grafted cyclotriphosphazene

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 = ClO4− or BF4-) salts forming the [FeL2]X2 complexes 1 and 2 respectively. For [FeL2](BF4)2 (2), the single crystal structure shows an ‘N6’ coordination sphere around the iron atom. UV–Vis, resonance Raman and Mössbauer 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.

Graphical abstractA new cyclotriphosphazene ligand substituted with a pendant 2,6-bis(benzimidazole-2-yl)pyridine (bbp) moiety has been used to synthesize iron(II) compounds with an ‘N’ iron(II)-bis-bbp core. Spectroscopic, magnetic and computational studies of the complexes have been conducted to determine the spin crossover behavior of the complexes. The complexes are low spin below 300 K but display spin crossover above this temperature.Figure optionsDownload full-size imageDownload as PowerPoint slide