Contribution of Coulomb Interactions to a Two-Step Crystal Structure Phase Transformation Coupled with a Significant Change in Spin Crossover Behavior for a Series of Charged Fe Complexes from 2,6-Bis(2-methylthiazol-4-yl)pyridine.

A series of [Fe(L)](BF) compounds were structurally and physically characterized (L = 2,6-bis(2-methylthiazol-4-yl)pyridine). A crystal structure phase transformation from dihydrate compound 1 to anhydrous compound 3 through partially hydrated compounds 2 and 2' upon dehydration was found. Compounds 1 and 3 exhibited a gradual spin crossover (SCO) conversion, whereas compounds 2 and 2' demonstrated two-step and one-step abrupt SCO transitions, respectively.

A New Family of Anionic Fe(III) Spin Crossover Complexes Featuring a Weak-Field N2O4 Coordination Octahedron.

Unprecedented anionic Fe(III) spin crossover (SCO) complexes involving a weak-field O,N,O-tridentate ligand were discovered. The SCO transition was evidenced by the temperature variations in magnetic susceptibility, Mössbauer spectrum, and coordination structure. The DFT calculations suggested that larger coefficients on the azo group in the HOMO-1 of a ligand might contribute to the enhancement of a ligand-field splitting energy.