Iron(III) Spin-Crossover Compounds with a Wide Apparent Thermal Hysteresis around Room Temperature

Abstract

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 (T(1/2) upward arrow = 352 K and T(1/2) downward arrow = 212 K) and 180 K (T(1/2) upward arrow = 392 K and T(1/2) downward arrow = 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 T(1/2(S1)) upward arrow = 215 K and T(1/2(S2)) upward arrow = 282 K, respectively. On the other hand, a one-step spin-crossover occurs at T(1/2) downward arrow = 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 T(1/2(S1)) upward arrow and T(1/2) downward arrow, and T(1/2(S2)) upward arrow and T(1/2) downward arrow, 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 pi interactions between quinoline and phenyl rings. Using a previously reported 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.

Spin-Singlet Transition in the Magnetic Hybrid Compound from a Spin-Crossover Fe(III) Cation and π-Radical Anion

“…The spectrum at 293 K consisted of mainly a broad asymmetric quadrupole doublet with isomer shift (IS) of 0.307(16) mm·s −1 and quadrupole splitting (QS) of 0.91(2) mm·s −1 . As compared with the [Fe(qsal) 2 ] complexes in the literature [29,[38][39][40], the IS value is very similar to those of the HS [Fe(qsal) 2 ] species, whereas the QS value is larger than those of the HS species. This large QS value may arise from the distortion of a coordination octahedron.…”

Temperature and pressure effects on the spin state of ferric ions in the [Fe(sal2-trien)][Ni(dmit)2] spin crossover complex

“…Combining SC and electrical conductivity was the aim of Dorbes et al [11] [12]. Analogously, similar properties have been studied on the salts of the [Fe(qsal) 2 ] + and Fe(R-salEen)] + complex cations as well [13][14][15][16][17][18][19].…”

Structures and Magnetic Properties of Iron(III) Complexes with Long Alkyl Chains

“…It has been known that the iron(III) compounds [Fe(pap) 2 ]X·H 2 O (Hpap = 2-(2-pyridylmethyleneamino)phenol, X = BF 4 − or ClO 4 − ) exhibit abrupt SCO behavior [11][12][13][14][15]. We suggested that the strong intermolecular interactions (π-π stacking, hydrogen bonding and so on) are important for cooperativity.…”

“…The solvent was removed in vacuo to yield a brown solid (0.96 g, 26%). 10,12,14,16) 5-Hydroxypyridine-2-carbaldehyde (3.30 mmol, 1 eq. ), K 2 CO 3 (3.30 mmol, 1 eq) and n-alkylbromide (3.50 mmol, n = 8-16) were stirred vigorously in dry DMF at 100 °C for 6 h. After cooling to room temperature, the solvent was removed in vacuo.…”