Die Kristallstruktur des gemischtvalenten Eisenfluoridhydrates Fe3F8 · 2 H2O

Crystal Structure of the Mixed-Valence Iron Fluorid Hydrate Fe₃F₈ · 2 H₂O Newly prepared was the red, monoclinic compound Fe₃F₈ · 2 H₂O, single crystals of which could be obtained under hydrothermal high pressure conditions (space group C2/m with a = 761.2(3), b = 750.0(1), c = 746.9(3) pm, β = 118.38(2)° and Z = 2). The X-ray structure determination (R_G = 0.0192 and 635 reflexions) yielded a framework structure, in which layers of octahedra 2[Fe^IIIF_6/2] are connected via corners of [Fe^IIF_4/2(H₂O)₂]-octahedra. The average distances in the nearly ideal octahedra are Fe^III? F = 193.0, Fe^II? F = 208.1 and Fe^II? OH₂ = 211.5 pm.     

Stationary points on the potential energy surface of O2−HF and O2−H2O

The determination of minima and saddle points on the potential energy surfaces of the hydrogen bonded species O₂^?HF and O₂^?H₂O is performed with unrestricted Hartree-Fock calculations. Geometries, electron density distributions, and relative energies for every stationary point are reported. Only one true minimum is found for O₂^?HF and for O₂^?H₂O, and this approximately corresponds to a structure where the partially positive hydrogen atom is located along one of the superoxide ion electron lone-pair directions. Calculated ΔH, ΔS, and ΔG values for the reaction between O₂^? and H₂O are in good agreement with experimental data.     

Theoretical studies of O2−:(H2O)n clusters

The interaction of superoxide ion O₂^? with up to four water molecules [O₂^?: (H₂O)_n, n = 1, 2, 4] has been investigated using ab initio molecular orbital theory. The binding energy of O₂^?: H₂O is calculated to be ?20.6 kcal/mol in good agreement with gas phase experimental data. At the MP3/6-31G^* level the O₂^?:H₂O complex has a C_2v structure with a double (cyclic) hydrogen bond between O₂^? and H₂O. A C_s structure with a single hydrogen bond is only 0.7 kcal/mol less stable. Interaction of H₂O with the doubly occupied π^* orbital of O₂^? is preferred slightly over interaction with the singly occupied π^* orbital. Natural bond orbital analysis suggests that both electrostatic and charge transfer interactions are important in anionic complexes. The charge transfer occurs predominantly in the O₂^? → H₂O direction and is important in determining the relative stabilities of the different structures and states. Singly and doubly hydrogen-bonded structures for the O₂^?: (H₂O)₂ and O₂^?: (H₂O)₄ clusters were found to be similar in stability and the increase in binding of the cluster becomes smaller as each additional water molecule is added to the cluster.     

Molekülstrukturen von Kupfer(II)- und Eisen(III)-Chlorokomplexen mit di- und monoprotoniertem N-(Pyrid-2-ylmethyl)ethylendiamin-N,N′,N′-triacetat (H2pedta−; Hpedta2−)

Molecular Structures of Copper(II) and Iron(III) Chloro Complexes with di- and monoprotonated N-(pyrid-2-ylmethyl)ethylenediamine-N,N′,N′-triacetate (H₂pedta^?; Hpedta^2?) The molecular structures of two complexes of di- and monoprotonated N-(pyrid-2-ylmethyl)ethylenediamine-N,N′,N′ -triacetate (pedta^3?) with Cu^II and Fe^III as central atoms have been determined by single crystal X-ray diffraction methods. Both complexes have a distorted octahedral coordination with H₂pedta^? and Hpedta^2? as pentadentate ligands and a chloride ion occupying the sixth coordination site. The different oxidation states of the central atoms result in a completely different coordination behaviour of the carboxyl groups. In both complexes one of the ? CH₂? COOH groups is uncoordinated. In the Fe^III complex, the central atom is coordinated by the hydroxylic O atoms of the deprotonated carboxyl groups. Contrary to this in the Cu^II complex, the central atom is coordinated by the carbonylic O atoms. One of the coordinated carboxyl groups is protonated and the other is deprotonated. All protonated carboxyl groups in both complexes form intermolecular hydrogen bonds.     

Syntheses and structural study of trinuclear iron acetates [Fe3O(CH3COO)6(H2O)3]Cl· 6H2O and [Fe3O(CH3COO)6(H2O)3] [FeCl4]· 2CH3COOH

The structure of two trinuclear iron acetates [Fe₃O(CH₃COO)₆(H₂O)₃]Cl· 6H₂O (I) and [Fe₃O(CH₃COO)₆(H_2O)₃][FeCl₄] · 2CH₃COOH (II) was determined by X-ray diffraction analysis. Crystals I and II are ionic and belong to the orthorhombic system with parameters a = 13.704(3), b = 23.332(5), c = 9.167(2) Å, R = 0.0355, space goup P2₁2₁2 for I and a = 10.145(4), b = 15.323(6), c = 22.999(8) Å, R = 0.0752, space group Pbc2₁ for II. The complex cation [Fe₃O(CH₃COO)₆(H₂O)₃]⁺ has a μ₃-O-bridged structure typical for trinuclear iron (III) compounds. As shown by Mössbauer spectroscopy, the iron(III) ions are in the high-spin state. In trinuclear cations, antiferromagnetic exchange interaction takes place between the Fe(III) ions with the exchange parameter J = -26.69 cm^?1 for II (Heisenberg-Dirac-Van Vleck model for D_3h, symmetry).     

Studies on the non-isothermal kinetics of thermal decomposition of the mixed ligand complex — [Fe2O(OC6H4CH=NC6H4O)2(C5H5N)4]·2H2O

The thermal decomposition of the mixed-ligand complex of iron(III) with 2-[(o-hydroxy benzylidene)amino] phenol and pyridine-[Fe₂O(OC₆H₄CH=NC₆H₄O)₂(C₅H₅N)₄]·2H₂O and its non-isothermal kinetics were studied by TG and DTG techniques. The non-isothermal kinetic data were analyzed and the kinetic parameters for the first and second steps of the thermal decomposition were evaluated by two different methods, the Achar and Coats-Redfern methods. Steps 1 and 2 are both second-order chemical reactions. Their kinetic equations can be expressed as: dα/dt=Ae^?E/RT(1-α)²     

Second-sphere effects on H2O2 activation by non-heme FeII complexes: role of a phenol group in the [H2O2]-dependent accumulation of FeIVO vs. FeIIIOOH

Redox metalloenzymes achieve very selective oxidation reactions under mild conditions using O₂ or H₂O₂ as oxidants and release harmless side-products like water. Their oxidation selectivity is intrinsically linked to the control of the oxidizing species generated during the catalytic cycle. To do so, a second coordination sphere is used in order to create a pull effect during the activation of O₂ or H₂O₂, thus ensuring a heterolytic O–O bond cleavage. Herein, we report the synthesis and study of a new non-heme Fe^II complex bearing a pentaazadentate first coordination sphere and a pendant phenol group. Its reaction with H₂O₂ generates the classical Fe^IIIOOH species at high H₂O₂ loading. But at low H₂O₂ concentrations, an Fe^IVO species is generated instead. The formation of the latter is directly related to the presence of the 2nd sphere phenol group. Kinetic, variable temperature and labelling studies support the involvement of the attached phenol as a second coordination sphere moiety (weak acid) during H₂O₂ activation. Our results suggest a direct Fe^II → Fe^IVO conversion directed by the 2nd sphere phenol via the protonation of the distal O atom of the Fe^II/H₂O₂ adduct leading to a heterolytic O–O bond cleavage.

A new Fe^II complex with a phenol group attached as a second coordination sphere moiety activates H₂O₂ to yield Fe^IVO following a mechanism reminiscent of peroxidase enzymes.     

Synthesis,structures and characterization of two new supramolecular coordination complexes with the ambidentate ligand 5-(4-pyridyl)-1,3,4-oxadiazole-2-thione (Hpot)

Two new coordination supramolecular complexes based on a versatile and unsymmetrical 5-(4-pyridyl)-1,3,4-oxadiazole-2-thione (Hpot) and Mn^II and Ni^II have been synthesized and structurally characterized by single-crystal X-ray diffraction analysis. Reaction of MnCl₂?· 4H₂O with Hpot afforded a neutral mononuclear complex [Mn(pot)₂(H₂O)₄]?·?2H₂O (1), which exhibits a three-dimensional (3-D) supramolecule through versatile intermolecular O–H?···?X (X=O, N and S) hydrogen bond interactions. When using NiCl₂?·?6H₂O instead of MnCl₂?· 4H₂O under similar reaction conditions, a neutral mononuclear complex [Ni(pot)₂(H₂O)₄] (2) is also obtained, which does not exhibit intermolecular hydrogen bonds and π–π stacking interactions. It is very interesting that the pot anion exhibits different coordination modes in complexes 1 and 2. The IR spectra and the TGA for 1 and 2 have been investigated and discussed in detail.     

Hydroxylation of Aromatics by H2O2 Catalyzed by Mononuclear Non-heme Iron Complexes: Role of Triazole Hemilability in Substrate-Induced Bifurcation of the H2O2 Activation Mechanism

Rieske dioxygenases are metalloenzymes capable of achieving cis-dihydroxylation of aromatics under mild conditions using O₂ and a source of electrons. The intermediate responsible for this reactivity is proposed to be a cis-Fe^V(O)(OH) moiety. Molecular models allow the generation of a Fe^III(OOH) species with H₂O₂, to yield a Fe^V(O)(OH) species with tetradentate ligands, or {Fe^IV(O); OH^.} pairs with pentadentate ones. We have designed a new pentadentate ligand, mtL₄², bearing a labile triazole, to generate an “in-between” situation. Two iron complexes, [(mtL₄²)FeCl](PF₆) and [(mtL₄²)Fe(OTf)₂]), were obtained and their reactivity towards aromatic substrates was studied in the presence of H₂O₂. Spectroscopic and kinetic studies reflect that triazole is bound at the Fe^II state, but decoordinates in the Fe^III(OOH). The resulting [(mtL₄²)Fe^III(OOH)(MeCN)]²⁺ then lies on a bifurcated decay pathway (end-on homolytic vs. side-on heterolytic) depending on the addition of aromatic substrate: in the absence of substrate, it is proposed to follow a side-on pathway leading to a putative (N₄)Fe^V(O)(OH), while in the presence of aromatics it switches to an end-on homolytic pathway yielding a {(N₅)Fe^IV(O); OH^.} reactive species, through recoordination of triazole. This switch significantly impacts the reaction regioselectivity.     

The calculation of the thermodynamic equilibrium in Fe3+/MoO 4 2− /H+(OH−)/H2O system and determination of reasonable conditions for iron molybdate deposition

The thermodynamic data on the Fe³⁺/MoO₄ ^2?/H⁺(OH^?)/H₂O system were analyzed. The iron(III) molybdate precipitates were studied by the X-ray phase analysis and electron probe microanalysis. It was shown that the content of the iron(III) oxide impurity in the precipitates depends on method and conditions of mixing of an iron precursor solution and an molybdenum precursor solution.     

Cs2.91Na1.34Fe3+0.25[Fe3O(SO4)6(H2O)3]·5H2O,a member of the Maus's salt family

The title compound, tricaesium sodium iron(III) μ₃‐oxido‐hexa‐μ₂‐sulfato‐tris[aquairon(III)] pentahydrate, Cs_2.91Na_1.34Fe³⁺_0.25[Fe₃O(SO₄)₆(H₂O)₃]·5H₂O, belongs to the family of Maus's salts, K₅[Fe₃O(SO₄)₆(H₂O)₃]·6H₂O, which is based on the triaqua‐μ₃‐oxido‐hexa‐μ‐sulfato‐triferrate(III) anion, [Fe₃O(SO₄)₆(H₂O)₃]⁵⁻, with Fe in a characteristically distorted octahedral coordination environment, sharing a common corner via an oxide O atom. Cs in four different cation sites, Na in three different cation sites and five water molecules link the anions in three dimensions and set up a crystal structure in which those parts parallel to (001) and within 0.05 < z < 0.95 have a distinct trigonal pseudosymmetry, whereas the cation arrangement and bonding near z∼ 0 generate a clear‐cut noncentrosymmetric polar edifice with the monoclinic space group C2. The structure shows some cation disorder in the region near z ∼ , where one Na atom in octahedral coordination is partly substituted by Fe³⁺, and a Cs atom is substituted by small amounts of Na on a separate nearby site. One Na atom, located on a twofold axis at z = 0 and tetrahedrally coordinated by four sulfate O atoms of two [Fe₃O(SO₄)₆(H₂O)₃]⁵⁻ units, plays a key role in generating the noncentrosymmetric structure. Three of the seven different cation sites are on twofold axes (one Na⁺ site and two Cs⁺ sites), and all other atoms of the structure are in general positions.     

Effect of Solvation on Chemical Reactions,I. Addition of a Single Water Molecule to the H− + H2O → OH− + H2 Reaction

The gas phase chemical reaction, H^? + H₂O → H₂ + OH, and the effect of an additional water molecule on the reaction, H^?(H₂O) + H₂O → H₂ + OH(H₂O), have been investigated. The optimal structures and energies of the reactants, products, two stable intermediates, and the transition state connecting the two intermediates have been determined. The additional water molecule does not affect the potential surface congruently: it destabilizes the H(H₂O) minimum, but stabilizes the H₂ ?OH minimum and the transition state connecting the two intermediates. However, it stabilizes the products more than the H₂ ?OH^? minimum. Finally, in line with the reduction in the barrier height, the transition state for the H(H₂0) to H₂ ?OH^? isomerization moves further along the reaction path.     

High Sensitive Microsensor Based on Organic‐Inorganic Composite for Two‐Dimensional Mapping of H2O2 by SECM

The present work describes the development of a selective, sensitive and stable sensing microsensor for scanning electrochemical microscopy (SECM) to measure H₂O₂ during electrochemical reduction of oxygen. The microsensor is based on graphene and Poly(3,4‐ethylenedioxythiophene) composite as support to iron (III) hexacyanoferrate (II) (PEDOT/graphene/Fe^III₄[Fe^II(CN)₆]₃ microsensor). The electrochemical properties of the PEDOT/graphene/Fe^III₄[Fe^II(CN)₆]₃ microsensor were investigated by cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM). The PEDOT/graphene/Fe^III₄[Fe^II(CN)₆]₃ microsensor showed an excellent electrocatalytic activity toward hydrogen peroxide (H₂O₂) reduction with a diminution of the overpotential of about 500 mV in comparison to the process at a bare gold microelectrode. The microsensor presented excellent performance for two dimensional mapping of H₂O₂ by SECM in 0.1 mol L^?1 phosphate buffer solution (pH 7.0). Under optimized conditions, a linear response range from 1 up to 1000 µmol L^?1 was obtained with a sensitivity of 0.08 nA L µmol^?1 and limit of detection of 0.5 µmol L^?1.     

Synthese und Strukturuntersuchungen von Ba2H[α-FeO4W12O36] · 26 H2O

Synthesis and Structure Studies of Ba₂H[α-FeO₄W₁₂O₃₆] · 26 H₂O The heteropolyanion compound Ba₂H[α-FeO₄W₁₂O₃₆] · 26 H₂O (I) crystallizes in the tetragonal space group P4 n2 with the lattice parameters a = 12.398(6), c = 18.721(6) Å; Z = 2; D_x = 4.128 g · cm^?3. The structure was solved on a twinned crystal from 1029 observed reflections and refined to an index R of 7.6%. The calculations were done by means of a modified ORFLS-programme by Eitel and Bärnighausen. The heteropolyanion [α-FeO₄W₁₂O₃₆]^5? has the well known α-Keggin structure. The average distance of the four central oxygen atoms to the Fe^III position (0, 0, 0) is 1.84 Å. The angles ? O? Fe? O are 112.3° (4X) and 103.9 (2X), respectively, which leads to an disphenoidal distortion of the FeO₄ tetrahedron. The powder and single crystal ESR spectra of I show the anisotropy of the Fe^III fine structure transition 1/2 ? ?1/2. The Mößbauer spectra confirm the tetragonal distortion of the central FeO₄ tetrahedron (quadrupole splitting Δ ≈ 0.50 mm · s^?1).     

Double Salt Formation in MBr2?M′ Br2?H2O and MCl2?M′Cl2?H2O systems (M,M′  Mg,Ca, Mn,Zn, Cd)

The CaBr₂? MnBr₂? H₂O and CdBr₂? MnBr₂? H₂O systems at 25°C have been studied. Two new double salts, CaBr₂ · MnBr₂ · 8 H₂O and 4 CdBr₂ · MnBr₂ · 10 H₂O, have been found. It was shown that for all known systems of the type MX₂? M′X₂? H₂O (M, M′ ? Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd; X ? Cl, Br), double salts are formed in all cases when both M²⁺ and M′²⁺ are p⁶, d⁵-HSS or d¹⁰ ions as well as in some cases when only one of the metal ions has these configurations. A comparison is made of the type and number of the double salts formed in a chloride and the corresponding bromide system.     

Synthesis,characterization and magnetic properties of mixed-valence iron complexes with 2-pyridyl oximes

Abstract

Two new mixed-valence iron complexes with 2-pyridyl oximes, [Fe(mpko)₃Fe(H₂O)₂(NO₃)](NO₃)·2H₂O (1) (mpko^? = methyl(2-pyridyl)ketone oximate) and [{Fe(dpko)₃}₂Fe](ClO₄)·4H₂O (2) (dpko^? = bis(2-pyridyl)ketone oximate), have been prepared by reaction of Fe^III with mpkoH in methanol (1) and Fe^II with dpkoH in methanol/water (2). Dinuclear Fe^II(low-spin)Fe^III(high-spin) and trinuclear Fe^II(low-spin)Fe^III(high-spin)Fe^II(low-spin) cations are present in the crystal structure of 1 and 2, respectively. Intermolecular hydrogen bonds in 1 lead to weak antiferromagnetic interactions between pairs of neighboring Fe^III centers, which allows observation of single-ion zero-field splitting effects.     

Redox Equilibria in the System Fe(OH)3(H2SO4)-Na2SO3-H2O Involving Precipitation of Iron(II) Sulfite as a Fe2O3 Precursor

Experimental data on the equilibria Fe²⁺/Fe³⁺ and SO₃ ²⁻/SO₄ ²⁻ in the system Fe(OH)₃(H₂SO₄)-Na₂SO₃-H₂O are presented. The quantitative relations between the reduction of Fe(III) and the precipitation of FeSO₃·2.5H₂O as a Fe₂O₃ precursor have considered graphically.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 1, 2005, pp. 41–44.Original Russian Text Copyright © 2005 by Vasekha, Motov.     

Synthesis, Characterization and Thermochemistry of 2MgO：B2O3：1.5H2O

Introduction　　 2MgO·B2 O3(Mg2 B2 O5)and 2MgO·B2 O3·H2 Omightbepreparedaswhiskermaterials .12MgO·B2 O3·H2 OnamedszaibelyiteisamagnesiumboratemineralwithastructuralformulaofMg2 [B2 O4 (OH) 2 ].2 Itisdifficulttosynthesizethiscompoundinthelaboratory .Recently ,weobtainedasimilarcompound 2MgO·B2 O3·1 5H2 Owhenwetriedtopreparewhiskerof 2MgO·B2 O3·H2 Obythephasetransformationof 2MgO·2B2 O3·MgCl2 ·14H2 OinH3BO3solutionunderhydrothermalcondition .Itishope fultopreparewh…     

Zur Kenntnis von Kaliumarseniten im Dreistoffsystem K2O?As2O3?H2O. Darstellung und Kristallstruktur von K3(HAs2O4)(As2O4) · 3/2 H2O

Concerning Potassium Arsenites in the Three-Component System K₂O? As₂O₃? H₂O. Preparation and Crystal Structure of K₃(HAs₂O₄) (As₂O₄) · 3/2 H₂O The phase K₃(HAs₂O₄)(As₂O₄) · 3/2 H₂O has been identified in the system K₂O? As₂O₃? H₂O at 40°C and characterized by X-ray structural analysis. In the crystal lattice independent polymetaarsenite anions, [HAs₂O₄^?]_n and [As₂O₄^2?]_n, adopt parallel zweier single chains.