Spin crossover behavior under pressure of Fe( PM-L)2(NCS)2 compounds with substituted 2′-pyridylmethylene 4-anilino ligands

New iron(II) spin crossover systems with large aromatic ligands, based on 2'-pyridylmethylene 4-anilino units, have been synthesized and studied. The whole range of spin crossover behavior has been observed, starting from pure high-spin to more or less complete gradual transitions and finally to discontinuous type transitions with both small and large hysteresis. Magnetic measurements under pressure have revealed that two of the compounds exhibit pressure-induced new phases with larger hysteresis than at atmospheric pressure. For one of the compounds the formation of this new phase is irreversible and the hysteresis width is similar to 100 K, as compared to 37 K before applying pressure. (C) 1998 Elsevier Science B.V, All rights reserved.