Anion-dependent spin crossover in solution for an iron(II) complex of a 1H-pyrazolyl ligand

The spin-crossover equilibrium midpoint temperature (T-1/2) in [Fe(3-bpp)(2)]X-2 (3-bpp = 2,6-di{pyrazol-3-yl}pyridine) varies from 259 K when X- = BPh4- to 277 K when X- = Br-, at 10 mM concentrations in an acetone-water solvent mixture.