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 ](NO 3 )·H 2 O (1), [Fe(dqmp) 2 ](BF 4 )·2CH 3 COCH 3 (2), and [Fe(dqmp) 2 ](ClO 4 ) (3) were synthesized from Fe(NO 3 ) 3 ·9H 2 O/Fe(ClO 4 ) 3 ·xH 2 O, NaBF 4 , 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, T 1 and T 2 , for 1 and 2 were determined and both increased with temperature from 220 to 380 K. The T 1 of 1 was larger than that of 2 at 380 K, and the T 1 values were larger than the T 2 values.