共查询到20条相似文献,搜索用时 31 毫秒
1.
We demonstrate that the devised incorporation of an alkylamine group into the second coordination sphere of an Fe II complex allows to switch its reactivity with H 2O 2 from the usual formation of Fe III species towards the selective generation of an Fe IV‐oxo intermediate. The Fe IV‐oxo species was characterized by UV/Vis absorption and Mössbauer spectroscopy. Variable‐temperature kinetic analyses point towards a mechanism in which the heterolytic cleavage of the O?O bond is triggered by a proton transfer from the proximal to the distal oxygen atom in the Fe II‐H 2O 2 complex with the assistance of the pendant amine. DFT studies reveal that this heterolytic cleavage is actually initiated by an homolytic O?O cleavage immediately followed by a proton‐coupled electron transfer (PCET) that leads to the formation of the Fe IV‐oxo and release of water through a concerted mechanism. 相似文献
2.
The ligand H 6ioan has been used to synthesize the three dinuclear complexes [(ioan)Mn IITi IV], [(ioan)Fe IITi IV], and [(ioan)Fe IIITi IV] +. The face-sharing bridging mode of the three phenolates provides short M-Ti IV distances of ≈3.0 Å. Mössbauer spectra of [(ioan)Fe IIITi IV] + show a magnetically split six-line spectrum at 3 K in zero magnetic field demonstrating a slow magnetic relaxation. Magnetic measurements provide a zero-field splitting of |D|=5 cm −1 in [(ioan)Fe IITi IV]. EPR spectroscopy demonstrates sizable zero-field splittings of the S=5/2 spin systems of [(ioan)Mn IITi IV] (D=0.246 cm −1) and [(ioan)Fe IIITi IV] + (D<−1 cm −1) that can be related to enforced covalency of the M-O ph bonds. [(ioan)Fe IIITi IV] + exhibits a reversible reduction at −0.26 V vs. Fc +/Fc demonstrating the facile accessibility of Fe III and Fe II. In contrast to an irreversible oxidation in [(ioan)Ni IITi IV] at 0.78 V vs. Fc +/Fc, the reversible oxidation at 0.25 V vs. Fc +/Fc in [(ioan)Mn IITi IV] indicates even the access of Mn III. These results indicate that pentanuclear complexes [(ioan)FeM 1M 2M 1Fe(ioan)] n+ are meaningful targets to access electron delocalization in mixed-valence systems over five ions due to the facile accessibility of both Fe II and Fe III in the terminal positions. This study provides important local spin-Hamiltonian and Mössbauer parameters that will be essential for the understanding of the potentially complicated electronic structure in the anticipated pentanuclear complexes. 相似文献
3.
Metal‐catalyzed nitrene transfer reactions arouse intense interest as clean and efficient procedures for amine synthesis. Efficient Rh‐ and Ru‐based catalysts exist but Fe alternatives are actively pursued. However, reactive iron imido species can be very short‐lived and getting evidence of their occurrence in efficient nitrene‐transfer reactions is an important challenge. We recently reported that a diiron(III,II) complex is a very efficient nitrene‐transfer catalyst to various substrates. We describe herein how, by combining desorption electrospray ionization mass spectrometry, quantitative chemical quench experiments, and DFT calculations, we obtained conclusive evidence for the occurrence of an {Fe IIIFe IV?NTosyl} intermediate that is very active in H‐abstraction and nitrene‐transfer reactions. DFT calculations revealed a strong radical character of the tosyl nitrogen atom in very low‐lying electronic configurations of the Fe IV ion which are likely to confer its high reactivity. 相似文献
4.
Cryogenically trapped Fe V nitride complexes with cyclam‐based ligands were found to decay by bimolecular reactions, forming exclusively Fe II compounds. Characterization of educts and products by Mössbauer spectroscopy, mass spectrometry, and spectroscopy‐oriented DFT calculations showed that the reaction mechanism is reductive nitride coupling and release of dinitrogen (2 Fe V?N→Fe II‐N?N‐Fe II→2 Fe II+N 2). The reaction pathways, representing an “inverse” of the Haber–Bosch reaction, were computationally explored in detail, also to judge the feasibility of yielding catalytically competent Fe V(N). Implications for the photolytic cleavage of Fe III azides used to generate high‐valent Fe nitrides are discussed. 相似文献
5.
The development of iron catalysts for carbon–heteroatom bond formation, which has attracted strong interest in the context of green chemistry and nitrene transfer, has emerged as the most promising way to versatile amine synthetic processes. A diiron system was previously developed that proved efficient in catalytic sulfimidations and aziridinations thanks to an Fe IIIFe IV active species. To deal with more demanding benzylic and aliphatic substrates, the catalyst was found to activate itself to a Fe IIIFe IVL . active species able to catalyze aliphatic amination. Extensive DFT calculations show that this activation event drastically enhances the electron affinity of the active species to match the substrates requirements. Overall this process consists in a redox self‐adaptation of the catalyst to the substrate needs. 相似文献
6.
Stabilization of 57Fe compounds in matrices of solid solutions of platinum(IV) superoxo- and hydroxo complexes was probed by Mössbauer spectroscopy. The ratio Fe III/Fe IV in these matrices is 20/1. 相似文献
7.
The autoxidation reaction of the Fe 2+/ethylenediaminetetraacetic acid system has been studied in solution phase at neutral pH and in solid state using Mössbauer spectroscopy. It was found that despite the proposed reaction pathway consisting of several reaction steps under similar circumstances, no intermediate species could be seen in the Mössbauer spectra and instead of the formation of the well-known [Fe III(EDTA)(H 2O)] ? species, the direct formation of its dimeric form was observed. 相似文献
8.
Identifying the active nucleophile in hydrolysis reactions catalyzed by binuclear hydrolases is a recurrent problem and a matter of intense debate. We report on the phosphate ester hydrolysis by a Fe IIIFe II complex of a binucleating ligand. This complex presents activities in the range of those observed for similar biomimetic compounds in the literature. The specific electronic properties of the Fe IIIFe II complex allowed us to use 1H NMR and Mössbauer spectroscopies to investigate the nature of the various species present in the solution in the pH range of 5–10. Both techniques showed that the hydrolysis activity is associated to a μ‐hydroxido Fe IIIFe II species. Further 1H NMR experiments show that binding of anions or the substrate changes this bonding mode suggesting that a terminal hydroxide is the likely nucleophile in these hydrolysis reactions. This view is further supported by the structure determination of the hydrolysis product. 相似文献
9.
A record anisotropy barrier (319 cm ?1) for all d‐f complexes was observed for a unique Fe II‐Dy III‐Fe II single‐molecule magnet (SMM), which possesses two asymmetric and distorted Fe II ions and one quasi‐ D5h Dy III ion. The frozen magnetization of the Dy III ion leads to the decreased Fe II relaxation rates evident in the Mössbauer spectrum. Ab initio calculations suggest that tunneling is interrupted effectively thanks to the exchange doublets. 相似文献
10.
Coordinatively unsaturated Fe III metal sites were successfully incorporated into the iconic MOF‐5 framework. This new structure, Fe III‐ iMOF‐5, is the first example of an interpenetrated MOF linked through intercalated metal ions. Structural characterization was performed with single‐crystal and powder XRD, followed by extensive analysis by spectroscopic methods and solid‐state NMR, which reveals the paramagnetic ion through its interaction with the framework. EPR and Mössbauer spectroscopy confirmed that the intercalated ions were indeed Fe III, whereas DFT calculations were employed to ascertain the unique pentacoordinate architecture around the Fe III ion. Interestingly, this is also the first crystallographic evidence of pentacoordinate Zn II within the MOF‐5 SBU. This new MOF structure displays the potential for metal‐site addition as a framework connector, thus creating further opportunity for the innovative development of new MOF materials. 相似文献
11.
Iron gallates with iron in the oxidation states Fe 2+ and Fe 3+ were prepared and studied by Mössbauer spectroscopy, X‐ray diffraction, and IR spectroscopy. Fe III 3,4,5‐trihydroxybenzoate (gallate) Fe(C 7O 5H 4) · 2H 2O, whose structure was first determined by Wunderlich, was obtained by the reaction of gallic acid and metallic iron or by oxidation of the Fe II gallate, which was obtained by the reaction of ferrous sulfate with 3,4,5‐trihydroxybezoic acid (gallic acid) under anoxic conditions. Trials to reproduce the hydrothermal preparation method of Feller and Cheetham show that the result depends crucially on the free gas volume in the reaction vessel. If there is no free volume one obtains the same Fe III gallate as in the other preparation methods. With a large free volume another compound was found to form whose composition and structure could not be determined. It could be specified only by Mössbauer spectroscopy. Fe III gallate, the Fe II gallate, and the new phase show magnetic ordering at liquid helium temperature. 相似文献
12.
Liquids trapped in the pores of certain silicate glasses (such as Corning Vycor ‘thirsty’ glass) were found to display frozen solutions like behavior at temperatures much higher than their actual freezing point. For example, recoilless γ-resonance absorption was observed for Mössbauer active solutes such as 119Sn and 57Fe salts at room temperature (i.e., without the need of quenching). Thus capillary Mössbauer spectroscopy (CMS) proved to be a new and useful experimental tool with great potential in solution chemistry. As part of a research project concerned with the hydrolysis of Sn II salts, we attempted to perform 119Sn CMS measurements for solutions containing stannous ion in a range of aqueous environments. Somewhat surprisingly, we found that under ambient conditions, Sn II aqueous liquid solutions, both the acidic and the basic systems, are essentially CMS-silent. This can be attributed to the strong temperature dependence of Lamb–Mössbauer factor of Sn II species, which may result in the complete disappearance of Mössbauer pattern well below room temperature. These observations can also explain why previous publications concerned with the use of CMS dealt exclusively with Sn IV and not with Sn II containing liquids. 相似文献
13.
We report the synthesis, characterization, and reactivity of [LFe 3(PhPz) 3OMn( sPhIO)][OTf] x ( 3 : x =2; 4 : x =3), where 4 is one of very few examples of iodosobenzene–metal adducts characterized by X‐ray crystallography. Access to these rare heterometallic clusters enabled differentiation of the metal centers involved in oxygen atom transfer (Mn) or redox modulation (Fe). Specifically, 57Fe Mössbauer and X‐ray absorption spectroscopy provided unique insights into how changes in oxidation state ( Fe III 2 Fe IIMn II vs. Fe III 3 Mn II ) influence oxygen atom transfer in tetranuclear Fe 3Mn clusters. In particular, a one‐electron redox change at a distal metal site leads to a change in oxygen atom transfer reactivity by ca. two orders of magnitude. 相似文献
14.
The precursor [Fe III(L)Cl (L = N, N′-bis(2′-hydroxy-3′-methyl-benzyliden)-1,7-diamino-4-azaheptane) is combined with [Mo(CN) 8] 4? yields a star shaped nona-nuclear cluster, [Mo IV{(CN)Fe III(L)} 8]Cl 4. This Fe 8Mo molecule is a high-spin system at room temperature. On cooling to 20 K some of the iron(III) centres in the molybdenum(IV)-star switch to the low-spin state as proven by Mössbauer spectroscopy. This molecule was deposited on TiO 2 nanowires by electrostatic interactions between the cluster cations and the surface functionalized titanium oxide nanowire. The synthesis and surface binding of the multistable molecular switch was demonstrated using IR and UV–Vis spectroscopy (high-resolution) transmission electron microscopy ((HR)TEM) and Mössbauer spectroscopy. High- and low-temperature Mössbauer spectra indicate that the spin state transition of the free cluster molecules is preserved after surface binding. The above results emphasize the possibility of fabricating molecule-based low-dimensional structures by using traditional bottom-up approaches based on the electrostatic interaction between the cluster cations and polymer functionalized nanowires. These results can be generalized for the application to both charged and non-charged molecules. 相似文献
15.
Ate-iron(II) species such as [Ar 3Fe II] − (Ar=aryl) are key intermediates in Fe-catalyzed couplings between aryl nucleophiles and organic electrophiles. They can be active species in the catalytic cycle, or lead to Fe 0 and Fe I oxidation states, which can themselves be catalytically active or lead to unwished organic byproducts. Analysis of the reactivity of the intermediates obtained by step-by-step displacement of the mesityl groups in high-spin [Mes 3Fe II] − by less hindered phenyl ligands was performed, and uncovered the crucial role of both steric and electronic parameters in the formation of the Fe 0 and Fe I oxidation states. The formation of quaternized [Ar 4Fe IIMgBr(THF)] − intermediates allows the bielectronic reductive elimination energy required for the formation of Fe 0 to be reduced. Similarly, the small steric pressure of the aryl groups in [Ar 3Fe II] − enables the formation of aryl-bridged [{Fe II(Ar) 2} 2(μ-Ar) 2] 2− species, which afford the Fe I oxidation state by bimetallic reductive elimination. These results are supported by 1H NMR, EPR, and 57Fe Mössbauer spectroscopies, as well as by DFT calculations. 相似文献
16.
Non‐heme (L)Fe III and (L)Fe III‐O‐Fe III(L) complexes (L=1,1‐di(pyridin‐2‐yl)‐ N, N‐bis(pyridin‐2‐ylmethyl)ethan‐1‐amine) underwent reduction under irradiation to the Fe II state with concomitant oxidation of methanol to methanal, without the need for a secondary photosensitizer. Spectroscopic and DFT studies support a mechanism in which irradiation results in charge‐transfer excitation of a Fe III?μ‐O?Fe III complex to generate [(L)Fe IV=O] 2+ (observed transiently during irradiation in acetonitrile), and an equivalent of (L)Fe II. Under aerobic conditions, irradiation accelerates reoxidation from the Fe II to the Fe III state with O 2, thus closing the cycle of methanol oxidation to methanal. 相似文献
17.
Nanocomposites containing magnetically active nanoparticles stabilized by the carbon-containing matrix formed in parallel were obtained by the polymerization—destruction synthesis. The composition, structure, and magnetic properties of nanocomposites synthesized by the thermal decomposition of unsaturated metal carboxylates and transition metal (CoII, NiII, FeIII) acrylamide complexes were studied by powder X-ray diffraction, scanning and transmission electron microscopy, and Mössbauer spectroscopy. The key macro stages and kinetic features of thermolysis of the metal-containing monomers were identified. The variation of the conditions of thermal transformations allows one to control the magnetic properties of nanocomposites from ferromagnetic to superparamagnetic behavior. 相似文献
18.
Acid and neutral Co II, Cu II, Ni II, Zn II, Fe II, and Fe III maleates, fumarates, and itaconates were obtained and characterized. The methods for their synthesis were optimized, and the valence state and coordination of metals were studied. Co II and Fe II hydrogen maleates, Co II maleate, and Co II fumarate were examined by X-ray diffraction analysis. The ligands based on unsaturated dicarboxylic acids can be mono-, bi-, and tetradentate, which results in the formation of acid salts, chain and three-dimensional coordination polymers, whose double bond is not involved in the coordination. The strong antiferromagnetic exchange (μ elf=1.41 and 0.34 μ B at 290 and 80 K, respectively) was detected in Cu II itaconate. Based on the data of Mössbauer spectroscopy, the partial reduction of Fe III to Fe II during the synthesis of Fe III maleate was shown to occur: δFe=0.43 and 1.27 mm s ?1, Δ E Q=0.57 and 3.13 mm s ?1 and Γ=0.37 and 0.28 mm s ?1 at T=298 K for Fe III and Fe II, respectively. 相似文献
19.
The preparation, electrical conductivity, magnetic moments, infrared, reflectance, and 57Fe Mössbauer spectra of tris(2,2,2-trichloroethoxy) iron(III) and its adducts with some oxygen and nitrogen donor ligands are reported. Cryoscopic data of the parent compound and its complex with ethylacetate suggest these compounds to be dimeric in nitrobenzene and benzene respectively. All the compounds are covalent with Fe III having distorted octahedral arrangement which is achieved through alkoxy bridging. The magnetic moments are lesser than those required for the spin only value indicating antiferromagnetic interactions in Fe III atoms. The Mössbauer spectra are explained in terms of two Fe III high spin sites corresponding to trans- and cis-positions in the structure. 相似文献
|