Mössbauer spectroscopic study of 57Fe species produced by 56Fe(n,γ)57Fe reaction in iron disulfide

In order to investigate the physical and chemical effects of neutron capture reaction, a neutron in-beam Mössbauer spectroscopic study on two isomorphs of iron disulfide: pyrite and marcasite, were carried out with a parallel plate avalanche counter at room temperature. In both compounds only two major products accounted for the obtained spectrum: one with Mössbauer parameters close to the parent compound and the other one considered to be a new product. The yield of the parent-like species was different in the two isomorphs.     

Preparation of57Fe enriched K4[Fe(CN)6] and K3[Fe(CN)6]

A simple method to prepare⁵⁷Fe enriched K₄[Fe(CN)₆] and K₃[Fe(CN)₆] is described. The yields of the products are much better than those reported in the literature so far. The enrichment is essential for⁵⁷Fe Mössbauer investigation in a variety of Prussiate type complexes and other inorganic compounds which are conveniently prepared from K₄[Fe(CN)₆] and K₃[Fe(CN)₆]. K₄[Fe(CN)₆] was obtained by reacting freshly prepared Fe(OH)₃ with glacial acetic acid and treating with iron acetate in boiling aqueous solution of KCN. The novel feature of the procedure to obtain K₃[Fe(CN)₆] is that the oxidation of K₄[Fe(CN)₆] has been carried out in the solid state by passing chlorine gas over the powdered specimen. K₃[Fe(CN)₆] was crystallised from alkaline solution of this oxidised powder. The compounds were characterised by Mössbauer spectroscopy.     

Preparative and structural studies on iron(II)-thiolate cyanocarbonyls: relevance to the [NiFe]/[Fe]-hydrogenases

A number of thermally stable iron(II)-thiolate cyanocarbonyl complexes, cis,cis-[Fe(CN)2(CO)2(CS3-S,S)]2-(1), mer-[Fe(CO)2(CN)3(NCCH3)]-(2)mer-[Fe(CO)3(CN)(CS3-S,S)]-(3), cis-[Fe(CO)2(CN)(S(CH2)2S(CH2)2S-S,S,S)]-(4), [Fe(CO)2(CN)3Br]2-(5), mer-[Fe(CO)2(CN)3(m-SC6H4Br)]2-(6) and mer-[Fe(CO)2(CN)3(SPh)]2-(7) were isolated and characterized by IR and X-ray diffraction analysis. The extrusion of one strong sigma-donor CN- ligand instead of CO from the iron(II) center of the thermally stable complexes [FeII(CO)2(CN)3Br]2-(5) containing less electron-donating bromide reflects the electron-rich character of the mononuclear [FeII(CN)2(CO)2(CS3-S,S)]2-(1) when ligated by by the bidentate thiolate, and the combination of one cyanide, two carbonyls and a tridentate thiolate provides the stable complex 4 as a result of the reaction of complex 5 and chelating ligand [S(CH2)2S(CH2)2S]2-. The preference of the sixth ligand coordinated to the unsaturated [FeII(CO)(CN)2(CS3-S,S)]2- Fe(II) center, the iron-site architecture of the bimetallic Ni-Fe active-site of [NiFe] hydrogenases, is a strong pi-acceptor CO group. Scrutiny of the coordination chemistry of iron(II)-thiolate cyanocarbonyl species [FeII(CO)x(CN)y(SR)z]n- reveals that certain combinations of thiolate, cyanide and carbonyl ligands (3 < or = y+z > or = 4) bound to Fe(II) are stable and this could point the way to understand the reasons for Nature's choice of combinations of these ligands in hydrogenases.     

DFT analysis: Fe4 cluster and Fe(110) surface interaction studies with pyrrole,furan, thiophene,and selenophene molecules

DFT studies of both the Fe₄ cluster and the Fe(110) surface interaction with pyrrole, furan, thiophene, and selenophene showed that selenophene forms a stabler adsorbate iron complex than the other heterocyclic molecules; this is consistent with the binding energy data that were calculated between the Fe cluster and the Fe(110) surface with the heterocycles. Furthermore, when the adsorption of the compounds with the iron cluster was analyzed by molecular orbital studies, the orbitals of selenophene overlapped more strongly with the Fe atom than that of the other molecules. In TD-DFT, the π → π* peak observed for the molecules disappeared when they formed complexes, and there appeared a charge transfer band (ligand to metal), thus confirming the coordination of these molecules with the cluster. The data suggest that the chemisorption is an exothermic process.     

Recent advances in synthesis and analysis of Fe(VI) cathodes: solution phase and solid-state Fe(VI) syntheses,reversible thin-film Fe(VI) synthesis,coating-stabilized Fe(VI) synthesis,and Fe(VI) analytical methodologies

Fe(VI) batteries based on unusual ferrate cathodic charge storage have been studied for quite a few years. So far, a class of Fe(VI) compounds have been successfully synthesized and studied as the cathodic materials in both alkaline and nonaqueous battery systems. This paper provides a summary of the syntheses of a range of Fe(VI) cathodes including the alkali Fe(VI) salts Li₂FeO₄, K _x Na_(2?x)FeO₄, K₂FeO₄, Rb₂FeO₄, Cs₂FeO₄, as well as alkali earth Fe(VI) salts CaFeO₄, SrFeO₄, BaFeO₄, and a transition metal Fe(VI) salt Ag₂FeO₄. Two synthesis routes summarized in this paper are the solution phase synthesis and the solid-state synthesis. Preparation of coating-stabilized (coated with KMnO₄, SiO₂, TiO₂, or ZrO₂) Fe(VI) cathodes and preparation of thin-film reversible Fe(VI/III) cathodes are also presented. Fe(VI) analytical methodologies summarized in this paper include Fourier transform infrared spectrometry, titrimetric (chromite), ultraviolet-visible spectroscopy, X-ray diffraction, inductively coupled plasma spectroscopy, Mössbauer spectrometry, potentiometric, galvanostatic, and cyclic voltammetry. Cathodic charge transfer of Fe(VI) is also briefly presented.     

A flow-through fluorescent sensor to determine Fe(III) and total inorganic iron

A flow-through fluorescent sensor for the consecutive determination of Fe(III) and total iron is described. The reactive phase of the proposed sensor, which has a high affinity for complexed Fe(III), consists of pyoverdin immobilized on controlled pore glass (CPG) by covalent bonding. This pigment selectively reacts with Fe(III) decreasing its fluorescence emission. Total inorganic iron is determined as Fe(III) after on-line oxidation in a mini-column containing persulphate immobilized on an ion exchange resin. The developed method allows the determination of Fe(III) in the 3-200 (g l(-1) range. The relative standard deviations of 10 determinations of 60 (g l(-1) of Fe(III) and 20 (g l(-1) of Fe(III)+Fe(II) are 3 and 5%, respectively. The sensor has been satisfactorily applied to speciate iron in synthetic, tap and well waters and wines. There were no significant differences for total inorganic iron determination between this new method and the atomic absorption spectroscopy reference method at the 95% confidence level. The sensor allows the concentration of Fe(II) to be calculated as the difference between total inorganic iron and Fe(III). The lifetime of the sensor is at least 3 months in continuous use or the equivalent of 1000 determinations.     

Manganoan rockbridgeite Fe4.32Mn0.62Zn0.06(PO4)3(OH)5: structure analysis and 57Fe Mössbauer spectroscopy

The structure of the basic iron phosphate rockbridgeite [iron manganese zinc tris­(phosphate) penta­hydroxide] was reinvestigated with special emphasis on the cation distribution deduced from new X‐ray and ⁵⁷Fe Mössbauer data. Rockbridgeite is orthorhombic, space group Cmcm, and shows three different Fe sites, one with symmetry, another with m symmetry and the third in a general position. One phosphate group has the P atom on a site with m symmetry, while the other has the P atom at a site with mm symmetry. Two Fe sites are fully occupied by ferric iron, while Mn³⁺ and Fe²⁺ are situated at a third, principally Fe, site. Structural data, bond‐valence sums and polyhedral distortion parameters suggest a new inter­pretation of the rockbridgeite ⁵⁷Fe Mössbauer spectrum.     

Thermal analysis of Fe(Co,Ni) based alloys prepared by mechanical alloying

In this work several Fe(Co,Ni) based nanocrystalline alloys were obtained by mechanical alloying. Thermal study was performed by differential scanning calorimetry and thermogravimetry. After 80 h milling, all DSC scans show several reactions on heating. At low temperature, about 400 K, the exothermal process detected is associated to structural relaxation. In all alloys, the main crystallization process begins over 700 K and has apparent activation energy values between 3.7 and 3.1 eV at^–1. The Co content increases the thermal stability of this process. Furthermore, thermomagnetic measurements confirm the Co solid solution into Fe. The ferromagnetic–paramagnetic transition occurs at about 900 K.     

Chalcogens as terminal ligands to iron: synthesis and structure of complexes with Fe(III)-S and Fe(III)-Se motifs

Metal complexes with terminal chalcogenido ligands are known for the early transition-metal complexes, yet for the heavier congeners (e.g., sulfido and selenido), there are no analogous examples for the late 3d metal ions. Reported herein is the isolation and characterization of monomeric iron(III) complexes containing sulfido and selenido ligands; isolation was accomplished using the tripodal ligand tris[(N'-tert-butylureaylato)-N-ethylene]aminato ([H3buea]3-). The FeIII-E (E = S2-, Se2-) complexes were prepared from the iron(II) precursor, [FeII(H3buea)]2-, and the elemental forms of the chalogen. The formulation of [FeIIIH3buea(S)]2- and [FeIIIH3buea(Se)]2- as monomeric complexes with Fe-E units is supported by spectroscopic, analytical, and X-ray diffraction studies. For instance, X-band EPR spectra contain well-resolved axial signals, which are consistent with each complex having S = 5/2 ground states. The solid-state molecular structures reveal FeIII-E bond lengths of 2.211(1) and 2.355(1) A for [FeIIIH3buea(S)]2- and [FeIIIH3buea(Se)]2-, respectively. The primary coordination sphere for each complex also contains three deprotonated urea nitrogen atoms from [H3buea]3-; the apical amine nitrogen atom weakly interacts with the iron centers at distances of greater than 2.6 A. The terminal chalcogenido ligands appear to weakly hydrogen-bond with the urea NH groups of the [H3buea]3-; however, open H-bond cavities are observed for [FeIIIH3buea(S)]2- and [FeIIIH3buea(Se)]2-, which may contribute to their observed long-term instability.     

Electron diffraction studies of the molecular structures of iron(II) chloride and iron(II) bromide. Evidence on the structure of dimeric species Fe2Br4

An expression for the extreme values of mean-square amplitudes of vibrations in polyatomic molecules has been derived which permits estimation of the mean-square amplitude without solving the vibrational problem. This expression can be improved for the stretching and scissoring modes when the assignment of frequencies is known. In turn, the corresponding vibrational frequency may be estimated from the experimental value of the mean-square amplitude. The mean-square amplitudes of the butadiene-1,3 molecule are considered as an example.     

Evaluation of matrix effect in isotope dilution mass spectrometry based on quantitative analysis of chloramphenicol residues in milk powder

In the present study, we developed a comprehensive strategy to evaluate matrix effect (ME) and its impact on the results of isotope dilution mass spectrometry (IDMS) in analysis of chloramphenicol (CAP) residues in milk powder. Stable isotope-labeled internal standards do not always compensate ME, which brings the variation of the ratio (the peak area of analyte/the peak area of isotope). In our investigation, impact factors of this variation were studied in the extraction solution of milk powder using three mass spectrometers coupled with different ion source designs, and deuterium-labeled chloramphenicol (D5-CAP) was used as the internal standard. ME from mobile phases, sample solvents, pre-treatment methods, sample origins and instruments was evaluated, and its impact on the results of IDMS was assessed using the IDMS correction factor (θ). Our data showed that the impact of ME of mobile phase on the correction factor was significantly greater than that of sample solvent. Significant ion suppression and enhancement effects were observed in different pre-treated sample solutions. The IDMS correction factor in liquid–liquid extraction (LLE) and molecular imprinted polymer (MIP) extract with different instruments was greater or less 1.0, and the IDMS correction factor in hydrophilic lipophilic balance (HLB) and mix-mode cation exchange (MCX) extract with different instruments was all close to 1.0. To the instrument coupled with different ion source design, the impact of ME on IDMS quantitative results was significantly different, exhibiting a large deviation of 11.5%. Taken together, appropriate chromatographic conditions, pre-treatment methods and instruments were crucial to overcome ME and obtain reliable results, when IDMS methods were used in the quantitative analysis of trace target in complex sample matrix.     

Five-coordinate iron(III) porphycenes: (1)H NMR, magnetic, and structural studies

Five-coordinate iron(III) 2,7,12,17-tetrapropylporphycene (TPrPc)Fe(III)X (X = C(6)H(5)O(-), Cl(-), Br(-), I(-), ClO(4)(-)) complexes have been investigated. The (1)H NMR spectra demonstrate downfield shifts for pyrrole resonances [(TPrPc)Fe(III)(C(6)H(5)O), 65.3 ppm; (TPrPc)Fe(III)Cl, 28.5 ppm] but large upfield ones for (TPrPc)Fe(III)Br (-7.8 ppm), (TPrPc)Fe(III)I (-49.4 ppm), and (TPrPc)Fe(III)ClO(4) (-77.1 ppm) (294 K, CD(2)Cl(2)). The pyrrole chemical shifts span the remarkable +70 to -80 ppm range. The variable-temperature (1)H NMR spectra of (TPrPc)Fe(III)X demonstrate anti-Curie behavior with a sign reversal for (TPrPc)Fe(III)Cl. These behaviors are consistent with the admixed S = 3/2, 5/2 ground electronic state with a dominating contribution of the S = 3/2 one. In terms of the chemical shift, (TPrPc)Fe(III)(ClO(4)) can be considered as an example of the purest S = 3/2 state in the investigated series. The extent of the S = 5/2 contribution in the admixed S = 3/2, 5/2 ground electronic state, as gradated solely the basis of the pyrrole proton paramagnetic shifts, is controlled by the strength of the axial ligand, following the magnetochemical series (Evans, D. R.; Reed, C. A. J. Am. Chem. Soc. 2000, 122, 4660). Significantly iron(III) 2,7,12,17-tetrapropylporphycene, soluble in typical organic solvents, can be considered as a universal framework to classify the ligand strength in a magnetochemical series, consistently using the beta-H pyrrole paramagnetic shifts as a fundamental criterion. The structure of (TPrPc)Fe(III)Cl has been determined by X-ray crystallography. The iron is five-coordinate with bonds of nearly equal length to the four pyrrole nitrogen atoms (Fe-N in the range 1.983(5)-2.006(6) A). The iron lies 0.583(1) A out of the mean plane of the macrocycle and 0.502(5) A out of the mean N(4) plane. In the solid, pairs of molecules are positioned about the center of symmetry so there is face-to-face pi-pi contact. The mean plane separation is 3.38 A, and the lateral shift of the porphycene center along the Fe-N bond is 4.490 A. The distance from one porphycene center to the other is 5.62 A, and the iron-iron separation is 6.304(2) A.     

The analysis of slag for copper,total iron,iron(II) and iron(III) by titration,controlled potential coulometry and electrodeposition

The interference of copper in the titrimetric determination of iron(II), iron-(III) and total iron in slags is discussed. The titration of iron(II) suggested by Bowen and Schairer is accurate and can be conducted with a reproducibility of ±0.29% at the 95% confidence level. Electrolytic copper-iron separation techniques were adapted to copper-containing iron-silicate slag, to obtain a reliable method for copper and total iron analysis. The theoretical and practical limitations for performing potentiostatic determinations of iron(III) in copper-containing slag are reviewed. Some determinatons were made but initial results were unreliable. Complete analyses of copper-gold alloys were made potentiostatically. Copper plus gold recoveries were ca. 99.8%.     

High-spin iron(III) complexes: structural,spectroscopic, and photochemical studies

Reaction of FeCl₃ with one equivalent of acac (acac = pentane-2,4-dionate) and KTp^Me2 (Tp^Me2 = hydrotris(3,5-dimethyl-pyrazol-1-yl)borate) yielded Tp^Me2Fe(acac)Cl (3), which upon reaction with methanolic solution of sodium azide resulted in the formation of a six coordinate compound Tp^Me2Fe(acac)N₃ (4) with a single azide. When the reaction of FeCl₃ and KTp^Me2 was performed with two equivalents of sodium azide and one equivalent of 3,5-dimethylpyrazole (Pz^Me2H), a six coordinate cis azide compound [Tp^Me2Fe(Pz^Me2H)(N₃)₂] (5) was obtained. These compounds were characterized by spectroscopic methods and single crystal X-ray crystallography. Electrochemical studies of 5 show that it can be irreversibly reduced at relatively lower potential than 4. The photolysis of 5 was performed at 77 K at different wavelengths (480, 419, and 330 nm) showing that 5 was photoreduced to a high-spin Fe(II) species instead of photooxidized to Fe(V).     

Synthesis, structure, and properties of an Fe(II) carbonyl [(PaPy3)Fe(CO)](ClO4): insight into the reactivity of Fe(II)-CO and Fe(II)-NO moieties in non-heme iron chelates of N-donor ligands

An Fe(II) carbonyl complex [(PaPy3)Fe(CO)](ClO4) (1) of the pentadentate ligand N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide (PaPy3H, H is the dissociable amide proton) has been synthesized and structurally characterized. This Fe(II) carbonyl exhibits its nu(CO) at 1972 cm(-1), and its 1H NMR spectrum in degassed CD3CN confirms its S = 0 ground state. The bound CO in 1 is not photolabile. Reaction of 1 with an equimolar amount of NO results in the formation of the {Fe-NO}7 nitrosyl [(PaPy3)Fe(NO)](ClO4) (2), while excess NO affords the iron(III) nitro complex [(PaPy3)Fe(NO2)](ClO4) (5). In the presence of [Fe(Cp)2]+ and excess NO, 1 forms the {Fe-NO}6 nitrosyl [(PaPy3)Fe(NO)](ClO4)2 (3). Complex 1 also reacts with dioxygen to afford the iron(III) mu-oxo species [{(PaPy3)Fe}2O](ClO4)2 (4). Comparison of the metric and spectral parameters of 1 with those of the previously reported {Fe-NO}6,7 nitrosyls 3 and 2 provides insight into the electronic distributions in the Fe(II)-CO, Fe(II)-NO, and Fe(II)-NO+ bonds in the isostructural series of complexes 1-3 derived from a non-heme polypyridine ligand with one carboxamide group.     

Iron (II) and iron (III) isotope exchange in water–dimethyl sulfoxide mixtures

The rate of the isotope exchange reaction between iron(II) and iron(III) perchlorates has been measured in a solvent mixture containing a 3:2 mole ratio of water to dimethyl sulfoxide over the temperature range from 25° to ?98°C. In this temperature range, the reactants can diffuse together faster than they can undergo isotope exchange. The activation enthalpy and entropy for the acid-independent reaction were 6.0 ± 1.2 kcal/mole and ?38 ± 17 cal/deg mole, respectively. Below ?22°C, the acid-dependent exchange reaction did not contribute significantly to the exchange. In liquid media at ?112° and ?117°C and in a solid glass at ?136°C, no isotope exchange was observed over the period of a calculated half-life for the reaction. At these temperatures, the rate at which the reactants diffuse together is slower than the calculated rate of isotope exchange. In a solid glass at ?196°C, no isotope exchange was observed over the period of one week.     

M(mu-CN)Fe(mu-CN)M' chains with phthalocyanine iron centers: preparation, structures, and isomerization

The molecular building blocks Fe(II)Pc (Pc = phthalocyaninato2-), Fe(III)Pc, ZnPc, Cp(dppe)Fe, and Cp(PPh3)2Ru were combined in the cyanide-bridged dinuclear reference compounds with M-CN-ZnPc and M-CN-FePc-CN arrays containing Fe(II)Pc and Fe(III)Pc. The linear trinuclear species with the M(mu-CN)Fe(mu-CN)M' backbone were prepared for both Fe(II)Pc and Fe(III)Pc centers, for terminal Fe/Fe, Fe/Ru, and Ru/Ru combinations and for all three possible cyanide orientations (M-CN-Fe-NC-M', M-CN-Fe-CN-M', and M-NC-Fe-CN-M'). The 15 complexes obtained were identified from their IR spectra and six structure determinations. The preferred orientation of the cyanide bridges could be established starting from the [Fe-NC-Fe(III)Pc-CN-Fe]+ complex, which is labile in solution and isomerizes to the corresponding [Fe-CN-Fe(III)Pc-NC-Fe]+ complex. A kinetic analysis of this isomerization has yielded an activation barrier of roughly 110 kJ/mol.     

Unusual structural types in polynuclear iron chemistry from the use of N,N,N',N'-tetrakis(2-hydroxyethyl)ethylenediamine (edteH4): Fe5, Fe6, and Fe12 clusters

The syntheses, crystal structures, and magnetochemical characterization of five new iron clusters [Fe5O2(O2CPh)7(edte)(H2O)] (1), [Fe6O2(O2CBut)8(edteH)2] (2), [Fe12O4(OH)2(O2CMe)6(edte)4(H2O)2](ClO4)4 (3), [Fe12O4(OH)8(edte)4(H2O)2](ClO4)4 (4), and [Fe12O4(OH)8(edte)4(H2O)2](NO3)4 (5) (edteH4= N,N,N',N'-tetrakis(2-hydroxyethyl) ethylenediamine) are reported. The reaction of edteH4 with [Fe3O(O2CPh)6(H2O)3](NO3) and [Fe3O(O2CBut)6(H2O)3](OH) gave 1 and 2, respectively. Complex 3 was obtained from the reaction of edteH4 and NaO2CMe with Fe(ClO4)3, whereas 4 and 5 were obtained from the reaction of edteH4 with Fe(ClO4)3 and Fe(NO3)3, respectively. The core of 1 consists of a [Fe4(mu3-O)2]8+ butterfly unit to which is attached a fifth Fe atom by four bridging O atoms. The core of 2 consists of two triangular [Fe3(mu3-O)]7+ units linked together by six bridging O atoms. Finally, the cores of 3-5 consist of an [Fe12(mu4-O)4(mu-OH)2]26+ unit. Variable-temperature (T) and -field (H) solid-state direct and alternating current magnetization (M) studies were carried out on complexes 1-3 in the 1.8-300 K range. Analysis of the obtained data revealed that 1, 2, and 3-5 possess an S = 5/2, 5, and 0 ground-state spin, respectively. The fitting of the obtained M/N(muB) vs H/T data was carried out by matrix diagonalization, and this gave values for the axial zero-field splitting (ZFS) parameter D of -0.50 cm-1 for 1 and -0.28 cm-1 for 2.     

Determination of metallic iron, iron(II) oxide, and iron(III) oxide in a mixture

A procedure is described for the estimation of metallic iron, ferrous oxide, and ferric oxide when present together. The sample is treated with bromine dissolved in ethanol, and filtered. Iron in the filtrate is titrated iodometrically, and corresponds to the metallic iron present in the mixture. The oxide residue is dissolved in hydrochloric acid under a carbon dioxide atmosphere. The iron(II) formed, equivalent to FeO present, is titrated with a standard vanadate solution, and the total iron(III) (FeO + Fe₂O₃) in the titrated solution is then estimated iodometrically.     

Novel Fe (III) heterochelates: Synthesis,structural features and fluorescence studies

Fluorescence properties of five 4-acyl pyrazolone based hydrazides (H₂SB_n) and their Fe (III) heterochelates of the type [Fe(SB_n)(L)(H₂O)]·mH₂O [H₂SB_n = nicotinic acid [1-(3-methyl-5-oxo-1-phenyl-4,5-di hydro-1H-pyrazol-4yl)-acylidene]-hydrazide; where acyl = –CH₃, m = 4 (H₂SB₁); –C₆H₅, m = 2 (H₂SB₂); –CH₂–CH₃, m = 3 (H₂SB₃); –CH₂–CH₂–CH₃, m = 1.5 (H₂SB₄); –CH₂–C₆H₅, m = 1.5 (H₂SB₅) and HL = 1-cyclopropyl-6-fluoro-4-oxo-7-(piperazin-1-yl)-1,4-dihydroquinoline-3-carboxylic acid] were studied at room temperature. The fluorescence spectra of heterochelates show red shift, which may be due to the chelation by the ligands to the metal ion. It enhances ligand ability to accept electrons and decreases the electron transition energy. The kinetic parameters such as order of reaction (n), energy of activation (E_a), entropy (S*), pre-exponential factor (A), enthalpy (H*) and Gibbs free energy (G*) have been reported.