Influence of Intermolecular Hydrogen Bonding to Spin Crossover Property of Iron （111） Complexes with a N3O2 Pentadentate Ligand and a Monodentate Ligand

Three iron （III） complexes with the formula of [Feat（X）L2]BPh4 were studied, in which a pentadentate Schiff-base ligand （H2L2 = bis （3-methoxysalicylideneiminopropyl） methylamine） and a counter anion BPh4 were fixed, and three monodentate ligands, 3-Mepy （3-methylpyridine）, 4-NH2py （4-aminopyridine）, and 2-Meim （2-methylimidazole） were used as the axial ligand X. The temperature dependence of magnetic susceptibility measurements demonstrated that [Fem（3-Mepy）L2]BPh4 showed a gradual spin equilibrium between HS （high-spin） （S = 5/2） and LS （low-spin） （S = 1/2） states, [Fem（4-NH2py）L2]BPh4 showed a steep SCO （spin crossover） and [FeIH（2-Melm）L2]BPh4 was in the HS state even at 100 K. The single crystal X-ray analyses demonstrated that [FelH（4-NH2py）L2]BPh4 has an one-dimensional chain structure constructed by intermolecular hydrogen bonding between 4-amino group of 4-NH2py and methoxy oxygen of adjacent molecular-cation. The crystal structure of [FenI（3-Mepy）L2]BPh4 has no such intermolecular interaction and its SCO site behaves independently, and the crystal structure of [FeIII（2-Meim）L2]BPh4 has a NH...n interaction between imidazole group of 2-Meim of cation and a phenyl group of anion BPh4. The result demonstrates that the intermolecular hydrogen bonding affects SCO profile significantly.