Syntheses and Characterization of Dinuclear High-Spin Iron(II,III) and (III,III) Complexes with 2,6-Bis[bis(2-benzimidazolylmethyl)aminomethyl]-4-methylphenolate(1—)

Abstract

Abstract Two types of dinuclear high-spin mixed valence iron(II,III) complexes, [Fe2(L-Bzim)(RCOO)2](BF4)2·nH2O (RCOO=CH3COO (1) or C6H5COO (2)), and [Fe2(L-Bzim)(C6H5COO)2(OH)]BF4·H2O (3), and dinuclear high-spin iron(III,III) complexes, [Fe2(L-Bzim)(CH3COO)2](ClO4)3·3.5H2O (4) and [Fe2(L-py)(C6H5COO)2](ClO4)3·CH3CN·H2O (5) were prepared, where L-Bzim is 2,6-bis[bis(2-benzimidazolylmethyl)aminomethyl]-4-methylphenolate(1—) and L-py is 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methylphenolate(1—). Mössbauer spectra of the mixed valence complexes revealed that they involve high-spin iron(II) and (III) ions in equimolar amount. Their ESR spectra exhibited a signal at gav=1.7 near liquid helium temperature characteristic of an antiferromagnetically spin coupled high-spin iron(II,III) dimer. Magnetic susceptibility measurements over the temperature range 80–300 K revealed that weak antiferromagnetic spin-exchange interactions are present between iron(II) and iron(III) ions (J≈−5 cm−1). The complexes showed an intervalence absorption band in the near infrared region, indicating that they belong to class II mixed valence type on the classification of Robin and Day. Cyclic voltammogram of 3 in acetonitrile showed two sets of reversible redox couples at 0.00 and 0.66 V vs. SCE, which are assigned to the redox reactions of Fe(II,III)/Fe(II,II) and Fe(III,III)/Fe(II,III), respectively. The complexes 4 and 5 exhibited weak antiferromagnetic interaction (J=−9–−12 cm−1). ESR spectra of 4 and 5 showed a significant temperature dependence.