Bistable Spin-Crossover in a New Series of [Fe(BPP-R)2] 2+ (BPP = 2,6-Bis(pyrazol-1-Yl)pyridine; R =CN) Complexes

A new series of iron(II) complexes—[Fe(BPP-CN)2](X)2, X = BF4 (1a-d) or ClO4 (2)—belonging to the [Fe(BPP-R)2]2+ (BPP = 2,6-bis(pyrazol-1-yl)pyridine) family of complexes showed abrupt and hysteretic, that is, bistable, spin-crossover (SCO) characteristics. Among the complexes, the lattice solvent-free complex 2 showed a stable and complete SCO (T1/2 = 241 K) with a thermal hysteresis width (ΔT) of 28 K, the widest ΔT so far reported for a [Fe(BPP-R)2](X)2 family of complex, showing abrupt SCO. The reproducible and bistable SCO shown by the relatively simple [Fe(BPP-CN)2](X)2 series of molecular complexes is encouraging to pursue [Fe(BPP-R)2]2+ systems for the realization of technologically relevant SCO complexes.