The magnetic properties of the spin-crossover compounds, [Fe(qsal)2]NCSe·MeOH (1) and [Fe(qsal)2]NCSe·CH2Cl2 (2), have been measured. We have discovered that both compounds 1 and 2 exhibit a wide thermal hysteresis loop of 140 K (T1/2↑ = 352 K and T1/2↓ = 212 K) and 180 K (T1/2↑ = 392 K and T1/2↓ = 212 K), respectively, in the first cycle. Thermogravimetric analysis shows that solvent molecules escape from compounds 1 and 2 around 340 and 395 K, respectively. This means that the hysteresis loops observed for the first cycle are only apparent ones. Following the first loop, they show a two-step spin-crossover in warming mode. The so-called "step 1" and "step 2" are centered around T1/2(S1)↑ = 215 K and T1/2(S2)↑ = 282 K, respectively. On the other hand, a one-step spin-crossover occurs at T1/2↓ = 212 K in cooling mode. The hysteresis widths can be estimated to be 3 K (step 1) and 70 K (step 2), assuming that the widths in steps 1 and 2 are defined as the differences between T1/2(S1)↑ and T1/2↓, and T1/2(S2)↑ and T1/2↓, respectively. The hysteresis width of 70 K in step 2 is one of the widest values reported so far for spin-crossover complexes. It is thought that the cooperativity operating in the complexes arises mainly from the intermolecular π interactions between quinoline and phenyl rings. Using a previously repored model, we are able to simulate the hysteresis loop with a two-step spin-crossover in warming mode and a one-step transition in cooling mode.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry