Spin crossover of a Fe(II) mononuclear complex induced by intermolecular factors involving chloride and solvent ordering.

Two new salts of a mononuclear tripodal Fe(II) complex were prepared, using ClO 4 - and Cl - . The ClO 4 - sample (1) remained HS at low temperatures, similar to the previously reported BF 4 - analogue. Crystallising with the Cl - anion (2) led to a markedly different crystal packing arrangement, and engendered SCO activity. This has been correlated to the lower crystal packing density in 2 and the coordination complex conformational differences arising due to the packing motifs of 1 and 2. Further, solvent ordering effects have been proposed to facilitate spin transition behaviour in 2.