Syntheses, three types of hydrogen-bonded assembly structures, and magnetic properties of [Fe^III(Him)₂(hapen)]Y·solvent (Him = imidazole, hapen =N,N′-bis(2-hydroxyacetophenylidene)ethylenediamine, y = BPh₄^-, CF₃SO₃^-, PF ₆^-, ClO₄^-, and BF₄ ^-)

Five iron(III) complexes of [Fe^III(Him)₂(hapen)] Y·solvent with five different counter anions were synthesized, where Him = imidazole, H₂hapen = N,N′-bis(2-hydroxyacetophenylidene) ethylenediamine, Y = BPh₄^- (1), CF₃SO ₃^- (2), PF₆^- (3), ClO ₄^- (4), and BF₄^- (5), and solvent = methanol or H₂O. Each Fe^III ion has octahedral coordination geometry with N₂O₂ donor atoms of the equatorial tetradentate ligand (hapen) and two nitrogen atoms of two imidazoles at the axial positions. The imidazole group is hydrogen-bonded to the phenoxo oxygen atom of hapen of the adjacent unit and/or to the counter anion or solvent molecule, to give three types of assembly structures involving linear dimer, cyclic dimer, and one-dimensional zigzag chain. Compound 1, with a cyclic dimer, and 2 and 3, with a one-dimensional chain, showed spin-equilibrium behavior between high-spin (S = 5/2) and low-spin (S = 1/2) states, whereas 4 and 5, with linear dimers, are high-spin complexes. Compound 3 shows abrupt spin transition with small thermal hysteresis.