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《Tetrahedron》1986,42(6):1721-1729
1,4-Dibromo- (8) as well as 1,4,7-trichloro- (11a) and 1,4,7-tribromotriquinacene (11b) react with Fe2(CO)9 in THF to yield (dihydroacepentalene)hexacarbonyldiiron complexes 9 and 10, the first representatives with a 7,10-dihydroacepentalene ligand. By reaction with Fe2(CO)9, the readily accessible 4,7-bis (dialkylamino)tricyclo[5.2.1.04.10]deca-1(10),2,5,8-tetraenes 14, derivatives of the unknown 4,7-dihydroacepentalene, were transfomed into their tricarbonyliron complexes 15. Upon reduction with sodium in THF, the η4-(diene)tricarbonyliron 15 selectively gave the novel 1,10η2-(olefin)tricarbonylferrates(-2)17 as a result of a twofold electron transfer. The intermediate green radical anion 16, which is persistent in the absence of excess sodium, was characterized by its ESR signal. Complexes 17 are the first of their class with complete structural characterization by 1H- and 13C-NMR spectroscopy. 相似文献
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A novel electrokinetic streaming potential technique has been used to determine the ζ potential behavior of three magnetic iron oxides, (Fe(3)O(4), γ-Fe(2)O(3), and CoFe(2)O(4)) as a function of pH and salt concentration. These colloidal materials, (nanosize in one dimension), are held in the form of a plug by means of external magnets. The streaming potential (E) is measured as a function of fluid flow induced by a pressure drop (ΔP) across the plug. The magnetically held plug is found to obey the requirements of the streaming potential technique; in each case an iso-electric point, (iep) independent of salt concentration is observed. However, if one uses the appropriate quantities in the standard formula, the calculated ζ potentials are very much lower than for oxides such as silica, alumina or goethite and other colloidal oxide, latex, etc. particulates in aqueous salt solutions. Furthermore, at a given pH, the measured ζ potentials anomalously increase in magnitude rather than decrease as observed conventionally as the salt concentration is increased. This apparent anomalous behavior could not be eliminated by incorporating surface conductance effects. However by including a conductance pathway, independent of pH or salt concentration, through the magnetic particle network itself, the anomaly was removed. Confirmation of the role of a conductance pathway through the magnetic particle network was obtained by using silica coated magnetic particles which displayed normal electrokinetic behavior. Finally, we have redesigned the plug-electrode assembly to allow measurement of streaming current, a technique know to eliminate contributions from plug network conductances of any kind. The resulting ζ potentials, derived from this streaming current technique are normal. 相似文献
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Anangamohan Panja Sanchita Goswami Nizamuddin Shaikh Partha Roy Mario Manassero Ray J. Butcher Pradyot Banerjee 《Polyhedron》2005,24(18):2921-2932
The reaction of copper chloride dihydrate and ferric chloride hexahydrate with a tripodal N4 ligand (ntb) under mild conditions affords two novel complexes [Cu(ntb)Cl]2[CuCl4] · 2H2O (1) and [Fe(ntb)Cl2]Cl · 3H2O (2). The reaction of ferric chloride with another N4 ligand, bispicpn, forms an octahedral mononuclear complex, [Fe(bispicpn)Cl2]Cl (3). Single-crystal X-ray structural studies of 1, 2 and 3 reveal the formation of hydrogen-bond sustained 3D, 2D and 1D networks, respectively, involving (N–HO) and (N–HCl) interactions. The packing arrangement in 2 further reveals the existence of hexagonal channels with helical propagation along the diagonal of the crystallographic b- and c-axes. The reactions of these complexes with 3,5-di-tert-butylcatechol have been studied in dimethylformamide. NMR techniques have been used to identify the reaction products. 相似文献
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Reactivity with hydrogen of pure iron oxide and of iron oxides doped with oxides of Mn,Co, Ni and Cu
Using dynamic TG in H2, X-ray powder diffraction and Mössbauer Spectroscopy the reactivities fot hydrogen reduction of Fe2O3 prepared at different temperatures, Fe2O3 doped with oxides of Mn, Co, Ni and Cu prepared at 300C from nitrate precursors and intermediate spinels derived from above samples during reduction have been explored. The reactivity is higher for finely divided Fe2O3 prepared at 250C. The reduction is retarded by Mn, marginally affected by Co and accelerated by Ni and Cu, especially at higher (5 at.%) dopant concentration. These reactivities confirmed also by isothermal experiments, are ascribed to the nature of disorder in the metastable intermediate spinels and to hydrogen spill over effects.
The authors thank Dr. Chitra Sankar for her help and useful discussions on the Mössbauer studies carried out. They also thank A. V. Narayan and D. Molliah for their assistance with the figures. 相似文献
Zusammenfassung Mittels Debye-Scherrer-Aufnahmen, Mössbauer-Spektroskopie und DTG in WasserstoffatmosphÄre wurde die ReaktivitÄt bezüglich der Reduktion mit Wasserstoff von Fe2O3, versetztem Fe2O3 und von intermediÄren Spinellen aus der Reduktion obiger Proben untersucht. Die reinen Fe2O3-Proben wurden bei verschiedenen Temperaturen hergestellt. Mit Oxiden von Mn, Co, Ni und Cu versetzte Fe2O3-Proben wurden bei 300C aus Nitrat-VorlÄufern hergestellt. Eine höhere AktivitÄt besteht für fein zerkleinertes, bei 250C hergestelltes Fe2)O3. Die Reduktion wird durch Mn verzögert, durch Co unwesentlich beeinflu\t und durch Ni und Cu beschleunigt, besonders bei höheren Konzentrationen (5 mol%). Diese ReaktivitÄten, die auch durch isotherme Experimente bestÄtigt werden konnten, wurden der Ungeordnetheit in den metastabilen intermediÄren Spinellen sowie Wasserstoff-überschu\-Effekten zugeschrieben.
The authors thank Dr. Chitra Sankar for her help and useful discussions on the Mössbauer studies carried out. They also thank A. V. Narayan and D. Molliah for their assistance with the figures. 相似文献
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Juliana da Silva Lima Fonseca Rodrigo Veiga T. de Albuquerque Marluce O. da Guarda Souza 《Reaction Kinetics and Catalysis Letters》2007,91(1):127-130
Textural and catalytic properties of iron oxides impregnated with copper acetate were investigated. In order to get satisfactory
performance in the high temperature shift reaction, 4 impregnation hours are necessary. 相似文献
8.
Šalitroš I Fuhr O Eichhöfer A Kruk R Pavlik J Dlháň L Boča R Ruben M 《Dalton transactions (Cambridge, England : 2003)》2012,41(17):5163-5171
The mononuclear compound (1) [Fe(II)(L)(2)](BF(4))(2) (L = 4-ethynyl-2,6-bis(pyrazol-1-yl)pyridine) was prepared and structurally as well as magnetically characterised. The crystallisation revealed the formation of two polymorphs--the orthorhombic 1A and the tetragonal form 1B. A third, intermediate phase 1C was found exhibiting a different orthorhombic space group. Reversibility of the phase transition between 1A and 1C was studied by variable-temperature single-crystal and powder X-ray diffraction studies, while an irreversible phase transition was observed for the transition of 1B→1C. The magnetic studies show that the 1A?1C transition is accompanied by a very abrupt spin transition (ST) with 8 K hysteresis width (T(1/2)(↓) = 337 K, T(1/2)(↑) = 345 K). The ST was confirmed by M?ssbauer spectroscopy as well as by DSC studies. In contrast, the 1B polymorph remained low-spin up to 420 K. In conclusion, a full cycle of intertwined phase- and spin-conversions of three polymorphs could be proven following the general scheme 1B→1C?1A. 相似文献
9.
We will provide an overview of the synthesis, structures, chemical and physical properties of novel iron oxides bearing FeO(4) square planar coordination, such as SrFeO(2) and Sr(3)Fe(2)O(5). The preparation of these materials relies on topotactic low-temperature reduction using metal hydrides. For instance, a simple 3D perovskite structure SrFeO(3) converts to a 2D structure SrFeO(2)via SrFeO(2.5). SrFeO(2) shows a remarkable stability against temperature and chemical substitution (for both A- and B-sites) and also tolerates distortions of square planes toward tetrahedra to adapt different A sites. Such structural stability and flexibility arise from strong covalent interactions not only through the in-plane Fe-O-Fe superexchange interactions but also through the out-of-plane Fe-Fe direct exchange interactions, and explains why SrFeO(2) exhibits magnetic order far beyond room temperature. The application of pressure on SrFeO(2) and Sr(3)Fe(2)O(5) further enhances the Fe-Fe direct exchange interactions and eventually induces striking transitions at around 34 GPa: spin-state transition from S = 2 to S = 1, insulator-to-metal transition, and antiferro-to-ferromagnetic transition. The high mobility of oxide ions at relatively low temperatures, during the reduction and reoxidation reaction process would offer an important challenge to tailor and design new solid oxide fuel cells/membranes toward lowering working temperatures. 相似文献
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Pichon C Dolbecq A Mialane P Marrot J Rivière E Sécheresse F 《Dalton transactions (Cambridge, England : 2003)》2008,(1):71-76
Two new insoluble transition metal substituted phosphotungstates, (C2N2H10)11[{(B-alpha-PW9O34)Fe3(OH)3}4(PO4)4Fe].38H2O(1) and K4(C2N2H10)12[(alpha-PW10Fe2O39)4].30H2O(2), have been isolated by the hydrothermal reaction of [A-alpha-PW9O34]9-, Fe(III) ions and ethylenediamine. Compound 1 has a tetrahedral symmetry and contains a Fe13 core built from the assembly of four Fe(III) trisubstituted [B-alpha-PW9O34]9- anions around a central disordered iron ion via four phosphato ligands. The anion in 2 can be described as a square of disubstituted [PW10O37]9- anions linked by Fe(III)-O-Fe(III) bridges. Magnetic measurements performed on 1 and 2 have shown the occurrence of antiferromagnetic interactions between the iron ions and have allowed the coupling constants between the magnetic centers to be determined. 相似文献
12.
Chikkali SH Gudat D Lissner F Nieger M Schleid T 《Dalton transactions (Cambridge, England : 2003)》2007,(35):3906-3913
Reaction of 3-[(diphenylphosphinyl)methyl]benzene-1,2-diol () and 4-[(diphenylphosphinyl)methyl]benzene-1,2-diol () with AgOTf or B(OH)(3) produced the bis-phosphine complexes , , or the borates , , respectively. All products were characterised by analytical and spectroscopic data and single-crystal X-ray diffraction studies. The anionic assembly was shown to act as a template-based chelate ligand toward Ag(+) by forming a neutral complex of composition [()Ag] with AgOTf. Spectroscopic and single-crystal X-ray diffraction studies revealed the presence of a kinetically very stable and conformationally rigid chelate that is best described as a bis-phosphine silver complex with a distinctly non-linear P-Ag-P array and two further secondary Ag-O interactions. Reaction of with AgOTf proceeded in a 2 : 2 molar ratio to give a dimeric product which was, on the basis of spectroscopic data, formulated as a macrocycle of composition [()(2)Ag(2)]. The different molecular sizes of and was underlined by PGSE NMR measurements which gave further evidence for the formation of solvent adducts between the chelate complex and DMF. Analysis of the (1)H,(109)Ag HMQC NMR spectra of provided evidence for a dependence of the (3)J(Ag,H) coupling on torsional angles which resembles a Karplus-type relationship. 相似文献
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The catalytic mechanism of the non-heme iron extradiol dioxygenases has been studied using hybrid density functional theory. These enzymes cleave a C-C bond outside the two hydroxyl groups of catechols, in contrast to the intradiol enzymes which cleave the C-C bond between these two groups. The chemical models used comprise about 70 atoms and include the first-shell ligands, two histidines, one glutamate, and one water, as well as some second-shell ligands, two histidines, one aspartate, and one tyrosine. Catechol is found to bind as a monoanion in agreement with experiments, while dioxygen is found to replace the water ligand. A spin-transition from the initial septet to a quintet state prepares the system for formation of a bridging peroxide with the catechol substrate. When the O-O bond is cleaved in the suggested rate-limiting step, a key substrate intermediate with partly radical and partly anionic character is formed. The partly anionic character is found to determine the selectivity of the enzyme. The results are compared to available experimental information and to previous studies. 相似文献
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Phenyl thiophosphonyl dichloride reacted with catechol n the presence of triethylamine to yield a pentacoordinated phosphorus compound 3. The reactions of a number of phosphorodi-chloridothioates with catechol gave a hexacoordinated phosphorus compound 8. The mechanism of these reactions are discussed. 相似文献
15.
Ricardo Baumhardt-Neto Srgio Emanuel Galembeck Ins Joekes Fernando Galembeck 《Journal of polymer science. Part A, Polymer chemistry》1981,19(3):819-829
Polytetrafluoroethylene (PTFE) surfaces can be modified by impregnation with Fe and Mn oxides by procedures based on Fe(CO)5 sorption in the polymer and followed by oxidation with H2O2 or KMnO4. The effect of some variables (reagent concentrations and temperature) on the amount of oxides deposited was examined. The oxides incorporated in PTFE can be only partly removed by acid cleaning. Water–PTFE contact angles and PTFE surface resistivity are altered. Electron and x-ray diffractograms of the oxides were obtained but unambiguous identification was not achieved. Transmission electron microscopy examination of surface replicas showed that impregnation with oxides which covered most of the PTFE surface was fairly uniform. 相似文献
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C. Noubactep A. Schöner H. Dienemann M. Sauter 《Journal of Radioanalytical and Nuclear Chemistry》2005,267(1):21-27
Summary The removal of uranium (VI) from zerovalent iron permeable reactive barriers and wetlands can be explained by its association
with iron oxides. The long term stability of immobilized U is yet to be addressed. The present study investigates the remobilization
of U(VI) from iron oxides via diverse reaction pathways (acidification, reduction, complex formation). Prior, uranium coprecipitation
experiments were conducted under various conditions. The addition of various amounts of a pH-shifting agents (pyrite), an
iron complexing agent (EDTA) or iron (III) reduction agent (TiCl3) yielded in uranium remobilization, concentrations above the US EPA allowedmaximum contaminant level(MCL=30 μg/l). This study
demonstrates that U(VI) release in nature strongly depends on the conditions and the mechanism of its fixation by geological
materials. 相似文献
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X-Ray and uv photoelectron spectra of FeO, Fe2O3, and Fe3O4 have been studied along with those of a few model compounds. It has been possible to assign distinct bands due to Fe2+ and Fe3+ in the 3d, 3p, 3s, and 2p bands of Fe3O4. The spectra of Fe3O4 do not show major changes through the Verwey transition. 相似文献
18.
Lempinen Janne Muuri Eveliina Lusa Merja Lehto Jukka 《Journal of Radioanalytical and Nuclear Chemistry》2018,316(2):717-723
Journal of Radioanalytical and Nuclear Chemistry - The sorption of inorganic radiocarbon on goethite, hematite and magnetite was studied as a function of carbon concentration, pH and ionic... 相似文献
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Tricarbonyl(3-ethoxy-4-phenyl-1-oxa-1,2,4-pentatrienone) iron(0) reacts with a variety of electron deficient and electron rich alkynes to produce catechol monoethyl ethers in moderate to good yield. Steric hindrance of the alkyne often exerts a stronger influence than electronic factors in determining the product distribution. The reaction with several alkyl, silyl, and aryl alkynes produced alkyne trimers as the major products. 相似文献
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Electronic structure of dinuclear iron nitrosyl complexes with different ligands at two iron centers
The electronic structures of three dinuclear iron complexes were determined with the DFT method. The complexes contain a {Fe(NO)2}9 unit and thiolate, nitrosyl, carbonyl and amine ligands at the second iron atom. The two iron atoms are bridged by thiolate ligands. In the lowest energy states of these complexes, the iron atoms possess spin S = 1, 3/2 or 5/2, depending on the coordinated ligands and their mutual arrangement. Nitrosyl is coordinated as NO− antiferromagnetically coupled to iron, and the two iron units are antiferromagnetically coupled to each other. 相似文献