Solvent Effects on the Spin Crossover Properties of Iron(II) Imidazolylimine Complexes

A series of Fe(II) complexes, fac-[Fe(4-ima-Bp)(3)](Y)(2)sol (Y = ClO4; sol = 3EtOH 1, 3MeOH 2; Y= BF4; sol = EtOH4H(2)O 3, 4H(2)O 4 and 3.5MeCN 5) have been prepared and structurally and magnetically characterized. The low temperature structures of 1, 2 and 5 have been determined by X-ray crystallography with LS Fe(II) centres found in all cases. Extensive C-H center dot center dot center dot pi interactions between the cations form 2D layers, which are linked to one another through N-H center dot center dot center dot O and O-H center dot center dot center dot O hydrogen bonds, resulting in high cooperativity. Despite 5 containing MeCN, N-H center dot center dot center dot O/F hydrogen bonds, and C-H center dot center dot center dot pi and pi-pi interactions combine to give similar 2D layers. Magnetic measurements reveal moderately abrupt spin crossover for 1-4; becoming more gradual and only 50% complete in 1 due to solvent loss. The MeCN solvate shows more gradual SCO and reinforces how subtle changes in packing can significantly influence SCO behaviour.