Light and thermally activated spin crossover coupled to an order-disorder transition of a propyl chain in an iron(III) complex

A series of three solvates [Fe(naphPren)2]I center dot CH2Cl2 1, [Fe(naphPren)(2)]I center dot CHCl3 2 and [Fe(naphPren)(2)]I center dot acetone 3 with the novel ligand HnaphPren {2-([(2-(propylamino)ethyl]imino)methyl)naphthalen-2-ol} is reported. Magnetic studies of these complexes reveal that 1 exhibits an abrupt SCO at 162 K, whereas 2 possesses a more gradual SCO centred at 172 K. 3 is trapped in the HS state, but irradiation at 980 nm enables accessibility to a hidden LS state via reverse-LIESST. The structures of 1-3 reveal that 1 and 2 show reversible disorder in the propyl group that is coupled to SCO which is absent in the acetone solvate. This study demonstrates how solvent subtly alters the packing impacting the potential flexibility of the propyl chain and thereby switching SCO on or off.