Syntheses and Characterization of Dinuclear Iron(II, II) and Iron(II, III) Complexes with a Dinucleating Ligand, 2,6-Bis[bis(2-pyridylmethyl)aminomethyl]-4-methylphenolate (1—)

Abstract

Dinuclear iron(II, II) complexes, [Fe2(L-py)(RCOO)2]BF4·nH2O (RCOO : CH3COO (1a) and C6H5COO (2a)), and two types of dinuclear mixed valence iron(II, III) complexes [Fe2(L-py)(RCOO)2](BF4)2·nH2O (RCOO : CH3COO (1b) and C6H5COO (2b)) and [Fe2(L-py)(CH3COO)(OH)](BF4)2·2H2O (3) were prepared, where L-py represents 2,6-bis[bis(2-pyridylmethyl)aminomethyl]-4-methyl-phenolate(1–). Only one of the two iron(II) ions in the iron(II, II) complexes is easily oxidized with molecular oxygen in methanol to form the mixed valence complexes, [Fe2(L-py)(RCOO)2](BF4)2·nH2O, which were characterized by chemical analyses and Mössbauer measurements. Magnetic susceptibility measurements over the temperature range 80–300 K revealed that high-spin iron(II) and iron(III) ions are antiferromagnetically coupled with the spin-exchange coupling constants J=−3–−8cm−1. The complexes exhibited an ESR signal of gav≈1.7 near liquid helium temperature. Such an ESR signal arises from an antiferromagnetically spin-coupled high-spin iron(II, III) dimer. An inter-valence charge-transfer transition was observed in the region 7000–8500 cm−1. The electron delocalization parameter α is estimated to be ca. 0.08, which corresponds to the class II mixed valence type in the classification of Robin and Day. Cyclic voltammogram of the complex 2b in acetonitrile showed two reversible couples at +0.05 and +0.73 V (vs. SCE), which were assigned to the redox reactions of Fe(II, III)/Fe(II, II) and Fe(III, III)/Fe(II, III), respectively. The comproportionation constants of 1b and 2b at 20 °C are 1.6×1012 and 5.0×1011, respectively, implying that the present mixed valence complexes are significantly stabilized.

Broken symmetry density functional study of a mixed‐valence unsymmetrical dinuclear iron complex

“…We have also computed the EPR g‐tensor for complex (1) at the B3LYP level of theory, obtaining the value of 2.03 averaged over the x, y and z components. The B3LYP calculated g value is in good agreement with the experimental values available from studies on mixed valence diiron complexes 48, which exhibited an ESR signal of g av ≈1.7 near liquid helium temperature for the complex with one phenolate and two carboxylate bridges 47.…”

“…This agreement shows that the use of the LS geometry to compute J seems to be more appropriate because the electron density of the LS state corresponds to the electron density of the real antiferromagnetic state, as was also pointed out by Neese and coworkers 36. Fortunately, for the case of compound (1), both values of J (computed using the HS or LS geometries) lies within the range of values for analogous mixed‐valence Fe(II)‐Fe(III) complex with a phenolate and two carboxylate bridging units ( J = (−3)‐(−8) cm −1 ) 47. In summary, we may say that the computed coupling constants for complex (1) are in very good agreement with the experimental values and are within the range expected experimentally for a mixed valence diiron complex with a μ‐phenolate and μ‐carboxylate ligands.…”

Versatile Reactivity of a Solvent-Coordinated Diiron(II) Compound: Synthesis and Dioxygen Reactivity of a Mixed-Valent FeIIFeIII Species

“…4) in a 1:1 ratio with δ = 0.48 mm/s, ΔE Q = 0.71 mm/s and δ = 1.17 mm/s, ΔE Q = 3.25 mm/s respectively, consistent with a high spin Fe(II)-Fe(III) formulation. 51 This observation is in accord with parameters observed in the case of its acetonitrile analog [Fe 2 ( N -Et-HPTB)( μ -PhCOO)(MeCN) 2 ](ClO 4 ) 3 31 (120 K, δ = 0.46 mm/s, ΔE Q = 0.52 mm/s; δ = 1.11 mm/s, ΔE Q = 3.06 mm/s) and other mixed valent compounds such as [Fe II Fe III BPMP(OPr) 2 (BPh 4 ) 2 25 , [Na][Me 4 N][Fe 2 (HXTA)(OAc) 2 ] 29 , [Fe II Fe III L-py(CH 3 COO) 2 ](BF 4 ) 2 28 , and [Fe II Fe III L-py(PhCOO) 2 ](BF 4 ) 2 28 . The observation of discrete quadrupole doublets for 5 at 77 K as well as at r.t. (Fig.…”

Phosphate Ester Hydrolysis: Metal Complexes As Purple Acid Phosphatase and Phosphotriesterase Analogues

“…Fe II Fe III complexes of symmetrical ligands have also been studied. Fe II Fe III complexes of 2,6‐bis{[bis(pyridin‐2‐ylmethyl)amino]methyl}‐4‐methylphenol (HBPMP; 7 ),61,98,99 4‐methyl‐2,6‐bis({[(6‐methylpyridin‐2‐yl)methyl](pyridin‐2‐ylmethyl)amino}methyl)phenol (HBPLMP; 8 ),90 2,6‐bis({[(6‐methylpyridin‐2‐yl)methyl](pyridin‐2‐ylmethyl)amino}methyl)‐4‐nitrophenol (HBPLNP; 9 )40 and 2,6‐bis{[bis(pyridin‐2‐ylmethyl)amino]methyl}‐4‐methoxyphenol (HBPMOP; 10 )100 have been reported. The syntheses are often, but not always, reported as being undertaken under an atmosphere of nitrogen.…”

“…The analogous symmetric ligands 2,6‐bis{[bis(pyridin‐2‐ylmethyl)amino]methyl}‐4‐methylphenol ( 7 )61,98,99 andA2,6‐bis{[(2‐hydroxybenzyl)(pyridin‐2‐ylmethyl)amino]methyl}‐4‐methylphenol ( 3 )96 permitted an assessment of the site‐specificity of the putative trivalent and divalent sites. The mixed Ga III Zn II complex of BPBPMP 2– and the digallium complexes of ligands 3 and 7 have been prepared and characterised 123.…”