Abstract
Binuclear iron (III) spin-crossover complexes, [Fe2 (salten)2(az)] (BPh4)2 (1) and [Fe2(salten)2(cc)](BPh4)2 (2) (H2salten= 2, 2'-[iminobis(3, 1-propanediylnitrilomethylidyne)]bis-phenol, az=4, 4'-azobis-pyridine, and cc=4, 4'-(1, 2-ethenediyl)bis-pyridine), and mononuclear iron (III) spin-crossover complexes, [Fe(pap)2]ClO4·H2O (3) (Hpap = 2-(2-pyridylmethyleneamino)phenol) and [Fe(qsal)2]NCSe·CH2Cl2 (4) (Hqsal = 2-[(8-quinolinylimino)methyl]-phenol), were synthesized and characterized by single-crystal X-ray diffraction, Mössbauer spectra, magnetic susceptibilities, and electronic spectra. The structures of 1 and 2 were determined in the low-spin states at 100 K and the high-spin states at 298 K. The complexes 1 and 2 exhibited the spincrossover behavior; gradual and rapid spin interconversion was observed by means of Mössbauer spectroscopy at 293 K. The structure of 3 in the high-spin state was determined at 293 K. The complex 3 exhibited the abrupt spin transition with thermal hysteresis (T1/2↑=180 K and T1/2↓=165 K). The time dependence of the magnetism and the frozen-in effect were observed for the complex 3. Furthermore, light-induced excited spin state trapping effect was observed for the first time for iron (III) complexes. The structure of 4 in the low-spin state was determined at 200 K. The complex 4 exhibited a wide thermal hysteresis loop of 180 K (T1/2↑ = 392 K and T 1/2↓ = 212 K) in the first cycle, although the hysteresis loop observed for the first cycle is apparent ones. Following the first loop, it shows a two-step spin transition in warming mode (T1/2 (S1) ↑ = 215 K and T1/2 (S2) ↑ = 282 K) and a one-step spin transition in cooling mode (T1/2 ↓ = 212 K).
