Solvent Dependent Spin-Crossover and Photomagnetic Properties in an Imidazolylimine FeII Complex

The synthesis and physico-chemical characterization of an Fe-II complex [Fe(L1)(3)](ClO4)(2)center dot CH3CN center dot 0.5H(2)O, 1, incorporating a bidentate imidazolylimine-based ligand are reported. Complex 1 crystallises as the mer-isomer and the crystal lattice is replete with hydrogen bonding interactions between ClO4- anions, solvent molecules and imidazole N-H groups. Variable-temperature structural, magnetic, photomagnetic and optical reflectivity techniques have been deployed to fully characterise the spin-crossover (SCO) behaviour in 1 along with its desolvated phase, 1 center dot desolv. Variable-temperature (1.8-300 K) magnetic-susceptibility measurements reveal a broad two-step full SCO for 1 (T-1/2 = 158 and 184 K) and photomagnetic experiments at 10 K under white-light irradiation revealed complete photo-induced SCO. 1 center dot desolv displays considerably different magnetic behaviour with sharp single-step SCO accompanied by a thermal hysteresis (T-1/2 up arrow = 105 K, T-1/2 down arrow = 95 K) in addition to full photo-induced SCO at lower temperatures.