The complex Tp(Ph,Me)NiS(2)CNMe(2) [Tp(Ph,Me) = hydrotris(3-phenyl-5-methyl- 1 -pyrazolyl)borate] features a bioinspired N3S2 ligand set supporting a five-coordinate, trigonally distorted square-pyramidal geometry in the solid state. Spin crossover of Ni(II) was demonstrated by temperature-dependent X-ray crystallography and magnetic susceptibility measurements. The crystal lattice contains two independent molecules (i.e., Nil and Ni2). At 293 K, the observed bond lengths and susceptibility are consistent with high-spin (S = 1) Ni(II), and both molecules exhibit relatively short axial Ni-N bonds and long Ni-N and Ni-S equatorial bonds. At 123 K, the Nil complex remains high-spin, but the Ni2 molecule substantially crosses to a structurally distinct diamagnetic (S = 0) state with significant elongation of the axial Ni-N bond and offsetting contraction of the equatorial bonds. The temperature-dependent susceptibility data were fit to a spin equilibrium at Ni2 [Delta H degrees = 1.13(2) kcal/mol and Delta S degrees = +7.3(1) cal mor(-1) K-1] consistent with weak coupling to lattice effects. Cooling below 100 K results in crossover of the Nil complex.