Mononuclear Fe(III) complexes with 2,4-dichloro-6-((quinoline-8-ylimino)methyl)phenolate: synthesis, structure, and magnetic behavior.

Three Fe(III)-based coordination complexes [Fe(dqmp)₂](NO₃)·H₂O (1), [Fe(dqmp)₂](BF₄)·2CH₃COCH₃ (2), and [Fe(dqmp)₂](ClO₄) (3) were synthesized from Fe(NO₃)₃·9H₂O/Fe(ClO₄)₃·xH₂O, NaBF₄, and 2,4-dichloro-6-((quinoline-8-ylimino)methyl)phenol (Hdqmp) in methanol/acetone and characterized. The structures of complexes 1–3 were determined via single-crystal X-ray crystallography at 100 K and room temperature, and their magnetic properties in the solid and solution forms were investigated. All complexes showed meridional structures with two tridentate dqmp⁻ ligands coordinated with Fe(III) cations. In the solid state, complex 1 showed an abrupt and complete spin crossover at 225 K, whereas complexes 2 and 3 exhibited an incomplete spin crossover at 135 and 150 K, respectively. In a dimethylformamide solution, the complexes showed counterion-dependent spin transitions. In contrast to the solid state, in solution, complex 1 did not exhibit complete spin crossover. However, complexes 2 and 3 showed more complete spin transitions in solutions than in the solid state. The relaxation times, T₁ and T₂, for 1 and 2 were determined and both increased with temperature from 220 to 380 K. The T₁ of 1 was larger than that of 2 at 380 K, and the T₁ values were larger than the T₂ values. [ABSTRACT FROM AUTHOR]