Spin transition at the mesophase transition temperature in a cobalt(II) compound with branched alkyl chains

A cobalt(II) compound, Co(C5C12C10-terpy)2](BF4)2 C5C12C10-terpy = 4',5' '-decyl-1' '-(heptadecyloxy)-2,2':6',2' '-terpyridine] with branched alkyl chains, based on a terpyridine frame, was synthesized. The cobalt(II) compound exhibits a spin transition between low-spin and high-spin with a thermal hysteresis loop (T(1/2) upward arrow = 288 K and T(1/2) downward arrow = 284 K) at the liquid-crystal transition temperature. It is the first example in the cobalt(II) compounds in which the spin transition occurs at the crystal-liquid crystal transition temperature.