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

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.

Resonance Raman spectroscopy of FeII FeIII and FeIII FeIII model complexes containing an unsymmetrical dinucleating ligand: a biomimetic redox pair for uteroferrin

“…27 However, this should not be confused with the weak antiferromagnetic coupling exhibited by the phenoxo bridges, which is caused by the low electronic density on the oxygen bridge. 31 Data for other iron complexes with phenolate ligands 33 show that tyrosinate-to-Fe III CT transition molar absorptivities are much higher than the phenolate(bridge)-to-Fe III analogs. As the RR intensification is proportional to the squared molar absorptivities, most of the RR enhanced bands of compounds 1 and 2 can be safely assigned to terminal phenolates.…”

Synthesis, molecular structure and spectroscopic, electrochemical and magnetic properties of a new dinuclear iron complex containing µ-sulfate-di-µ-alkoxo bridges: evaluating the influence of the sulfate bridge on the physicochemical properties of the di-µ-alkoxo-diiron unit

“…The water molecule is disordered over two alternative positions with occupancy factors of 0.54(4) and 0.46 (4) and its H atoms and the H atom of the methanol solvent were not found on the Fourier map. Although complex 3 crystallizes in a non-centrosymmetric space group, the absolute structure was not established.…”

“…From the data it becomes evident that the change in the third bridging group from acetate (monoanion) to sulfate (dianion), although not affecting significantly the structural parameters, has an important influence on the electronic properties of these complexes. In fact, this effect may be related to the decrease in the Lewis acidity of the iron centers, due to the increase in the number of better O-donor (OAc -and SO 4 2-in 1 and 3, respectively, instead of H 2 O in 2) groups which makes the energy of the t 2g orbitals in 3 and 1 higher than that in 2 and therefore, higher energy radiation is necessary to promote the LMCT process. Similar behavior has been observed when the acetate bridges in the complex [Fe 2 (BBPMP)(OAc) 2 ] 2+ 8,2006 (λ max = 601 nm) 5 are replaced by sulfate bridges, resulting in the complex [Fe 2 III (BBPMP)(SO 4 ) 2 ] (λ max = 587 nm).…”

“…These compounds have been prepared mainly on the 1,3-diamino-2-hydroxypropane 2,3 or 2,6-bis(aminomethyl)-4-methylphenol skeleton. [4][5][6][7] Purple acid phosphatases (PAPs) are iron-containing non-heme proteins involved in the regulation of phosphate and phosphorylated metabolite levels in a wide range of organisms. They have been isolated from a variety of mammalian (TRAP, ufPAP, bsPAP), plant (kbPAP, spPAP) and bacterial sources (afPAP, ncPAP).…”

“…[2][3][4][5][6][7][16][17][18][19] This is due to the high ε values observed in electronic spectra of PAPs, which are attributed to a tyrosine→Fe III charge transfer transition. Thus, such dinucleating ligands hold the two metal centers in close proximity and provide phenolate coordinating groups, allowing the study of the influence of such groups on the properties exhibited by the metal centers in the complexes as well as in the enzyme.…”