Effect of N 4-substituent choice on spin crossover in dinuclear iron(II) complexes of bis-terdentate 1,2,4-triazole-based ligands

Abstract

Seven new dinuclear iron(II) complexes of the general formula [Fe II2(PMRT)2](BF4)4· solvent, where PMRT is a 4-substituted-3,5-bis{[(2-pyridylmethyl)-amino]methyl}- 4H-1,2,4-triazole, have been prepared in order to investigate the substituent effect on the spin crossover event. Variable temperature magnetic susceptibility and 57Fe Mössbauer spectroscopy studies show that two of the complexes, [FeII2(PMPT)2](BF4) 4·H2O (N4 substituent is pyrrolyl) and [FeII2(PMPhAT)2](BF 4)4 (N4 is N,N-diphenylamine), are stabilized in the [HS-HS] state between 300 and 2 K with weak antiferromagnetic interactions between the iron(II) centers. Five of the complexes showed gradual half spin crossover, from [HS..