Mesophase and magnetic behavior in cobalt(II) and iron(II) compounds

The metal complexes with long alkyl chains [Co(C16-terpy)(3)](BF(4))(2) (1) and [Fe(C16-terpy)(2)](BF(4))(2) (2) were synthesized and the physical properties of the complex were characterized by magnetic susceptibility, Mossbauer spectroscopy, polarizing optical microscopy, differential scanning calorimetry, and X-ray scattering, where C16-terpy is 4'-hexadecyloxy-2,2':6',2 ''-terpyridine. Variable-temperature magnetic susceptibility measurements and/or Mossbauer studies revealed that the complex 1 exhibited unique spin transition (T(1/2)down arrow = 217 K and T(1/2)up arrow = 260 K) induced by structural phase transition, and the complex 2 was in the low-spin state in the temperature region of 5-400 K before the first mesophase transition. The cobalt(II) and iron(II) complexes exhibited liquid-crystal properties in the temperature range of 371-528 K and 466-556 K, respectively. After mesophase transition, the complex 1 exhibited only slight spin transition (T(1/2)down arrow = 266 K and T(1/2)up arrow = 279 K), and the complex 2 was in the low-spin state. The compounds with multifunction, i.e., magnetic property and liquid-crystal properties, are important in the development of molecular materials. (c) 2009 Elsevier Ltd. All rights reserved.