Iron(III) spin transition compound with a large thermal hysteresis

The magnetic properties of the spin-crossover compound, [Fe(qsal) ₂ ]NCSe·2DMSO (N-(8-quinolyl)-salicyladimine) (1), have been measured. We have discovered that the compound 1 exhibits a wide "thermal hysteresis loop" of 115 K (T _1/2 ↑ = 324 K and T _1/2 ↓ = 209 K) in the first cycle. Thermogravimetric analysis shows that solvent molecules of the compound 1 are removed at around 324 K. This means that the hysteresis loop observed for the first cycle is only an apparent one. Following the first loop, the compound 1 shows a spin-crossover in warming mode. The spin transition occurs at T _1/2 ↑ = 285 K and T _1/2 ↓ = 209 K and the hysteresis width can be estimated to be 76 K, which is one of the largest values reported so far for spin-crossover compounds. It is thought that the cooperativity produced in the compound mainly arises from the intermolecular π interactions between the quinoline and the phenyl rings.