Spin-crossover iron(II) compounds with liquid-crystal properties

Abstract

The iron(II) compounds [Fe(1C16-O-bzimpy) 2](BF 4) 2 ( 1) and [Fe(2C16-bzimpy) 2](BF 4) 2 ( 2) were synthesized and the physical properties of the compounds were characterized by polarizing optical microscopy, differential scanning calorimetry, and powder X-ray analysis, where 1C16-O-bzimpy and 2C16-bzimpy are 2,6-bis(benzimidazol-2′-yl)-4-hexadecyloxypyridine and 2,6-bis( N-hexadecylbenzimidazol-2′-yl)pyridine, respectively. The iron(II) compounds 1 and 2 have exhibited crystal-liquid crystal transition at 547 K and 322 K, respectively. Variable-temperature magnetic susceptibility measurements and/or Mössbauer studies reveal that the compound 1 exhibits spin-crossover behavior between high-spin and low-spin states and photo-induced spin transition from a low-spin state to a metastable high-spin state, and the compound 2 is in the low-spin state. Therefore, the iron(II) compound 1 can undergo spin-crossover, photo-induced spin transition and liquid-crystal properties in a compound. The compounds with multifunction, i.e. spin-crossover and photo-induced spin transition material with liquid-crystal properties, are important in the development of molecular switches and optical materials.