Syntheses, three types of hydrogen-bonded assembly structures, and magnetic properties of [FeIII(Him)2(hapen)]Y·solvent (Him = imidazole, hapen =N,N′-bis(2-hydroxyacetophenylidene)ethylenediamine, Y = BPh4−, CF3SO3−, PF6−, ClO4−, and BF4−)

Five iron(III) complexes of [FeIII(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), CF3SO3− (2), PF6− (3), ClO4− (4), and BF4− (5), and solvent = methanol or H2O. Each FeIII 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.

Graphical abstractFive iron(III) complexes with the formula [FeIII(Him)2(hapen)]Y·solvent were synthesized, where Him = imidazole, H2hapen = N,N′-bis(2-hydroxyacetophenylidene)ethylenediamine, Y = BPh4− (1), CF3SO3− (2), PF6− (3), ClO4− (4), and BF4− (5). The complex cation has an octahedral six-coordinated geometry, consisting of an equatorial tetradentate ligand (hapen) and two imidazoles (Him) at the axial positions. The imidazole group is hydrogen-bonded to the phenoxo oxygen of the adjacent hapen unit or a solvent molecule to give the assembly structures. Compound 1 with a cyclic dimer bridged by two solvent molecules is spin equilibrium. Compounds 2 and 3 with one-dimensional chain structure are spin-equilibrium complexes. Compound 3 shows abrupt spin transition. Compounds 4 and 5 with linear dimer are high-spin complexes.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Five Fe(III) complexes of [FeIII(Him)2(hapen)]Y·solvent were synthesized. ► Fe(III) ion is coordinated by a tetradentate ligand and two imidazoles. ► Imidazole group is hydrogen bonded to phenoxo oxygen of adjacent complex. ► Linear dimer, cyclic dimer, and one-dimensional zigzag chain are generated. ► 1D Fe(III) compound shows abrupt spin transition with thermal hysteresis.