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 up arrow = 288 K and T-1/2 down 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.