New Octahedral, Head-Tail Iron(II) Complexes with Spin Crossover Properties

The synthesis and characterisation of four new Schiff base-like ligands with long alkyl chains in the outer periphery and their iron(II) complexes with methanol and pyridine as axial ligands is reported. Two of the methanol complexes crystallise in a lipid layer-like arrangement with the alkyl chain (tail) packed in the middle and the iron centres (head) in the outer sites. The pyridine complexes show varying types of spin transition (step wise, incomplete, with hysteresis), which depends on the alkyl chain length and substituents in the outer periphery of the ligand. Investigations in solution using 1H NMR spectroscopy demonstrate that the differences in the spin transition behaviour are due to packing effects as the same transition curve is obtained independently of the alkyl chain length.