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A series of iron(II) complexes with the general formula [FeII(L2-Qn)(L)]n+ (n = 1, L = F−, Cl−; n = 2, L = NCMe, H2O) have been isolated and characterized. The X-ray crystallographic data reveals that metal–ligand bond distances vary with varying ligand field strengths of the sixth ligand. While the complexes with fluoride, chloride and water as axial ligand are high spin, the acetonitrile-coordinated complex is in a mixed spin state. The steric bulk of the quinoline moieties forces the axial ligands to deviate from the Fe–Naxial axis. A higher deviation/tilt is noted for the high spin complexes, while the acetonitrile coordinated complex displays least deviation. This deviation from linearity is slightly less in the analogous low-spin iron(II) complex [FeII(L1-Qn)(NCMe)]2+ of the related asymmetric ligand L1-Qn due to the presence of only one sterically demanding quinoline moiety. The two iron(II)-acetonitrile complexes [FeII(L2-Qn)(NCMe)]2+ and [FeII(L1-Qn)(NCMe)]2+ generate the corresponding iron(IV)-oxo species with higher thermal stability of the species supported by the L1-Qn ligand. The crystallographic and spectroscopic data for [FeIV(O)(L1-Qn)](ClO4)2 bear resemblance to other crystallographically characterized S = 1 iron(IV)-oxo complexes. The hydrogen atom transfer (HAT) and oxygen atom transfer (OAT) reactivities of both the iron(IV)-oxo complexes were investigated, and a Box–Behnken multivariate optimization of the parameters for catalytic oxidation of cyclohexane by [FeII(L2-Qn)(NCMe)]2+ using hydrogen peroxide as the terminal oxidant is presented. An increase in the average Fe–N bond length in [FeII(L1-Qn)(NCMe)]2+ is also manifested in higher HAT and OAT rates relative to the other reported complexes of ligands based on the N4Py framework. The results reported here confirm that the steric influence of the ligand environment is of critical importance for the reactivity of iron(IV)-oxo complexes, but additional electronic factors must influence the reactivity of iron-oxo complexes of N4Py derivatives. [ABSTRACT FROM AUTHOR]

Using the pentadentate ligand (N-bis(1-methyl-2-benzimidazolyl)methyl-N-(bis-2-pyridylmethyl)amine, 2pyN2B), presenting two pyridyl and two (N-methyl)benzimidazolyl donor moieties in addition to a central tertiary amine, new MnII and MnIV-oxo complexes were generated and characterized. The [MnIV(O)(2pyN2B)]2+ complex showed spectroscopic signatures (i.e., electronic absorption band maxima and intensities, EPR signals, and Mn K-edge X-ray absorption edge and near-edge data) similar to those observed for other MnIV-oxo complexes with neutral, pentadentate N5 supporting ligands. The near-IR electronic absorption band maximum of [MnIV(O)(2pyN2B)]2+, as well as DFT-computed metric parameters, are consistent with the equatorial (N-methyl)benzimidazolyl ligands being stronger donors to the MnIV center than the pyridyl and quinolinyl ligands found in analogous MnIV-oxo complexes. The hydrogen- and oxygen-atom transfer reactivities of [MnIV(O)(2pyN2B)]2+ were assessed through reactions with hydrocarbons and thioanisole, respectively. When compared with related MnIV-oxo adducts, [MnIV(O)(2pyN2B)]2+ showed muted reactivity in hydrogen-atom transfer reactions with hydrocarbons. This result stands in contrast to observations for the analogous FeIV-oxo complexes, where [FeIV(O)(2pyN2B)]2+ was found to be one of the more reactive members of its class. [ABSTRACT FROM AUTHOR]

The heterodinuclear mixed-valence complex [FeMn(ICIMP)(OAc)2Cl] ( 1) {H2ICIMP = 2-( N-carboxylmethyl)-[ N-( N-methylimidazolyl-2-methyl)aminomethyl]-[6-( N-isopropylmethyl)-[ N-( N-methylimidazolyl-2-methyl)]aminomethyl-4-methylphenol], an unsymmetrical N4O2 donor ligand} has been synthesized and fully characterized by several spectroscopic techniques as well as by X-ray crystallography. The crystal structure of the complex reveals that both metal centers in 1 are six-coordinate with the chloride ion occupying the sixth coordination site of the MnII ion. The phenoxide moiety of the ICIMP ligand and both acetate ligands bridge the two metal ions of the complex. Mössbauer spectroscopy shows that the iron ion in 1 is high-spin FeIII. Two quasi-reversible redox reactions for the complex, attributed to the FeIIIMnII/FeIIMnII (at -0.67 V versus Fc/Fc+) and FeIIIMnII/FeIIIMnIII (at 0.84 V), were observed by means of cyclic voltammetry. Complex 1, with an FeIII-MnII distance of 3.58 Å, may serve as a model for the mixed-valence oxidation state of purple acid phosphatase from sweet potato. The capability of the complex to effect organophosphate hydrolysis (phosphatase activity) has been investigated at different pH levels (5.5-11) by using bis(2,4-dinitrophenyl)phosphate (BDNPP) as the substrate. Density functional theory calculations indicate that the substrate coordinates to the MnII ion. In the transition state, a hydroxide ion that bridges the two metal ions becomes terminally coordinated to the FeIII ion and acts as a nucleophile, attacking the phosphorus center of BDNPP with the concomitant dissociation of the leaving group. [ABSTRACT FROM AUTHOR]

The dinuclear complex [Zn2(papy)2] ·2CH3OH [H2papy = N-(2-hydroxybenzyl)- N-(2-picolyl)glycine] was synthesized and characterized. The crystal structure of the complex reveals that both ZnII ions are pentacoordinate with distorted pentagonal bipyramidal coordination arrangements. The phenoxyl groups of each ligand bridge the two metal atoms, whereas each carboxylate of the ligand is terminally bound to one ZnII ion. Potentiometric studies of the ZnII:H2papy system in a methanol/water mixture show the existence of a mononuclear species at lower pH; but at a pH above 5, a dimeric species starts to dominate and transforms further into a bis(μ-phenoxo) bridged dizinc complex by deprotonation of phenolic hydrogen. A kinetic study of the hydrolysis of bis(2, 4-dinitrophenyl)phosphate at different pH, catalyzed by complex 1, indicates a maximum rate at pH 9, where the bis(μ-phenoxo)-bridged dizinc species corresponding to 1 dominates in solution. [ABSTRACT FROM AUTHOR]

Abstract: The orange–red colored complexes of the type [Fe(LSB)Cl3], 1, have been synthesized in excellent yields by reacting FeCl3·6H2O with LSB in methanol. Here, LSB is (2-(ethylthio)-N-(pyridin-2-ylmethyl)ethanamine), (LSB 1) and (2-(benzylthio)-N-(pyridin-2-ylmethyl)ethanamine) (LSB 2). Similarly, FeCl3·6H2O reacted with 2-(((2-(ethylthio) ethyl) (pyridin-2-ylmethyl)amino)methyl)phenol (HL1), 2-(((2-(ethylthio)ethyl)(pyridin-2 ylmethyl)amino)methyl)-4-nitrophenol (HL2), 4-chloro-2-(((2-(ethylthio)ethyl)(pyridin-2-ylmethyl)amino)methyl)phenol (HL3), 2-(((2-(benzylthio)ethyl)(pyridin-2-ylmethyl) amino)methyl)phenol (HL4), 2-(((2-(benzylthio)ethyl)(pyridin-2-ylmethyl)amino)methyl) -4-nitrophenol (HL5), and 4-chloro-2-(((2-(benzylthio)ethyl)(pyridin-2-ylmethyl)amino) methyl)phenol (HL6) to give dichloro complexes of the type [Fe(L)Cl2], 2. The solid and solution structure of the complexes, as well as their properties, were probed using X-ray diffraction, spectroscopic and electrochemical methods. The Mössbauer spectral study at 80K for complexes reveals the existence of (III) oxidation state and high-spin state of the metal center in the complex. Dioxygenase activity of the complexes has been studied and both 1 and 2 have been found to display the intradiol-cleaving pathway. However, no extradiol cleavage products have been isolated. [ABSTRACT FROM AUTHOR]

Abstract: The N4O3 coordinating heptadentate ligand afforded the mononuclear [FeIII(HL)][BPh4] (1) and binuclear [Fe2 IIIL(OAc)2][BPh4] (2) complexes. In complex 1, the ligand binds in a trianionic N2O3 fashion whereas in the case of 2 the ligand binds in the trianionic N4O3 form in which the iron ions are held together by μ-phenoxo and bis μ-acetato bridges. In 1, the Fe(III) center has a trigonal bipyramidal geometry (τ =0.84) whereas in 2 both the Fe(III) centers have a distorted octahedral geometry. Complex 2 shows an intramolecular weak antiferromagnetic interaction. Gas phase geometry optimizations have been performed using density functional theory without any symmetry constraints. The gas phase optimized structures agree well with the X-ray structure. [Copyright &y& Elsevier]