One-Dimensional Spin-Crossover Iron(II) Complexes Bridged by Intermolecular Imidazole−Pyridine NH···N Hydrogen Bonds, [Fe(HLMe)3]X2 (HLMe = (2-Methylimidazol-4-yl-methylideneamino-2-ethylpyridine; X = PF6, ClO4, BF4)

2-Methylimidazol-4-yl-methylideneamino-2-ethylpyridine (abbreviated as HLMe) is the 1:1 condensation product of 2-methyl-4-formylimidazole and 2-aminoethylpyridine and functions as a bidentate ligand to the iron(II) ion to produce the 3:1 complexes together with anions, [Fe(HLMe)3]X2 (X = PF6 (1), ClO4 (2), BF4 (3)). The magnetic susceptibilities, differential scanning calorimetric measurements, and Mossbauer spectral measurements demonstrated that complexes 1, 2, and 3 showed a steep one-step spin crossover (SCO) between the high-spin (HS, S = 2) and low-spin (LS, S = 0) states with small thermal hysteresis. Three complexes have an isomorphous structure and are crystallized in the same monoclinic space group, C2/c, both in the HS and LS states. The iron(II) ion has the octahedral coordination geometry of a facial isomer with N6 donor atoms of three bidentate ligands, in which an imidazole and an imine nitrogen atom per ligand participate in the formation of the coordination bond, but the pyridine nitroge...