The synthesis and physico-chemical characterization of an FeII complex [Fe(L1)3](ClO4)2·CH3CN·0.5H2O, 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·desolv. Variable-temperature (1.8–300 K) magnetic- susceptibility measurements reveal a broad two-step full SCO for 1 (T1/2=158 and 184 K) and photomagnetic experiments at 10 K under white-light irradiation revealed complete photo-induced SCO. 1·desolv displays considerably different magnetic behaviour with sharp single-step SCO accompanied by a thermal hysteresis (T1/2›=105 K, T1/2fl=95 K) in addition to full photo-induced SCO at lower temperatures.