若干线型Mo-Fe-S簇合物红外光谱及其与结构关系的研究

对若干线型Mo一Fe一S簇合物[Cl2FeS2MoS2FeCl2][-2](1)、[S2MoS2FeCl2]^2^-(2)、[S2MoS2Fe(SPh)2][2-](3)、[S2MoS2FeS2Fe(SPh)2][3-](4)、[S2MoS2FeS2MoS2][3-](5)、Cl2FeS2FeCl2][2-](6)、[(PhS)2FeS2Fe(SPh)2][2-](7)的红外光谱进行了研究。通过比较它们的特征频率、结构参数和金属原子的氧化态,对νMo-St、νMo-SbνFe-Sb、νFe-SPh、νFe-Cl进行了归属。并对δS-Mo-S的归属作了初步探讨。文中讨论了MoS2Fe单元中Mo原子对νFe-Sb的影响, 通过振动频率与结构关系的研究揭示其内在联系及规律性。对两条途径的亲电诱导效应进行了讨论, 并提出一个能定性标志Fe→Mo电荷迁移大小的有用参数Δν值。     

Structural conversions of molybdenum-iron-sulfur edge-bridged double cubanes and P(n)-type clusters topologically related to the nitrogenase P-cluster

Edge-bridged Mo-Fe-S double cubanes are versatile precursors for the synthesis of other clusters of the same nuclearity. Thus, the double cubane [(Tp)(2)Mo(2)Fe(6)S(8)(PEt(3))(4)] sustains terminal ligand substitution with retention of the Mo(2)Fe(6)(micro(3)-S)(6)(micro(4)-S)(2) core structure and rearrangement to the Mo(2)Fe(6)(micro(2)-S)(2)(micro(3)-S)(6)(micro(6)-S) topology of the nitrogenase P(N) cluster upon reaction with certain nucleophiles. Four distinct processes for the conversion of double cubanes to P(N)-type clusters are documented, affording the products [(Tp)(2)Mo(2)Fe(6)S(9)(SR)(2)](3)(-), [(Tp)(2)Mo(2)Fe(6)S(8)(OMe)(3)](3)(-), and [(Tp)(2)Mo(2)Fe(6)S(7)(OMe)(4)](2)(-). In the latter clusters, two methoxides are terminal ligands and one or two are micro(2)-bridging ligands. The reverse transformation of a P(N)-type cluster to an edge-bridged double cubane has been demonstrated by the reaction of [(Tp)(2)Mo(2)Fe(6)S(8)(OMe)(3)](3)(-) with Me(3)SiX to afford [(Tp)(2)Mo(2)Fe(6)S(8)X(4)](2)(-) (X = Cl(-), Br(-)). Edge-bridged double cubanes have been obtained in the oxidation states [Mo(2)Fe(6)S(8)](2+,3+,4+). The stable oxidation state of P(N)-type clusters is [Mo(2)Fe(6)S(9)](+). Structures of five double cubanes and four P(N)-type clusters are reported. The P(N)-type clusters are synthetic representations of the biologically unique topology of the native P(N) cluster. Best-fit superpositions of the native and synthetic cluster cores gives weighted rms deviations in atom positions of 0.20-0.38 A. This study and an earlier investigation (Zhang, Y.; Holm, R. H. J. Am. Chem. Soc. 2003, 125, 3910-3920) provide a comprehensive account of the synthesis of structural analogues of the native P(N) cluster and provide the basis for continuing investigation of the synthesis of weak-field Mo-Fe-S clusters related to nitrogenase. (Tp = tris(pyrazolyl)hydroborate(1-).)     

The structural rule of Mo—Fe—S cluster compounds

By means of the structural rule, 9N-L, of transition metal cluster compounds, a relationship between the spin property and the structure of Mo-Fe-S clusters is proposed. The relationship can be further revealed by performing EHMO quantum chemical calculations. Also the theoretical maximum values of spin are in accordance with experimental results.     

若干中性配体对Mo—Fe—S簇合物自兜的影响

通过电子吸收光谱的变化研究了一些含N和含P中性配体对MoS_4~(2-)-nFeCl_2-DMF体系形成立方烷型Mo-Fe-S簇合物的可能影响。     

An organometallic approach to the synthesis of high nuclearity Mo-Fe-S clusters as potential models for the iron-molybdenum cofactor of nitrogenase

Reaction of the [Fe₂S₂(CO)₆]^2– dianion with molybdenum reagents produces a number of high-nuclearity Mo-Fe-S carbonyl clusters with Fe/Mo ratios 5, as well as a variety of new Fe-S carbonyl clusters. The former are particularly relevant as models or precursors to models for the iron-molybdenum cofactor [FeMo-cofactor] of nitrogenase. General strategies for the synthesis of FeMo-cofactor models are briefly reviewed, and the structures of clusters produced in the [Fe₂S₂(CO)₆]^2–/Mo systems examined to date are described.     

Investigation on Oxidation-Reduction Properties of Some Fe-S and Mo-Fe-S Clusters

Oxidation-reduction properties of some Fe-S and Mo-Fe-S clusters have been studied by cyclic voltammetric measurement. It is indicated that there are some factors which affect the oxidation- reduction properties of clusters, of which are charge density of metal atom in cluster core, electron effect of ligands, charge and geometric configurations of the reactant particle, etc.     

Pdn(n=1-7)团簇及其与甲烷相互作用的密度泛函理论研究

用密度泛函理论(DFT)的B3LYP方法, 对Pdn(n=1-7)团簇的几何结构、振动频率及其与甲烷分子间的相互作用进行了理论研究. 结果表明, 随着Pd原子数增多, 团簇结构对团簇大小的依赖性减弱, 结构参数向金属晶体趋近. 在Pdn(n=1-7)团簇上, 甲烷的表面吸附作用较弱. Pd2CH4中, 甲烷受到两个Pd原子的活化作用, 活化程度增强, 吸附能增大. 在PdnCH4 (n=1, 3-7)体系中, 甲烷的吸附能随着团簇模型的增大而减小, 趋近于其在金属晶面上的吸附能.     

Investigation of the structural units of germanium sulfide and selenide by quantum chemical methods

This article deals with the modeling of the structural units (clusters) of germanium sulfide and germanium selenide glasses by quantum chemical (ab initio Hartree–Fock) methods. Clusters of different sizes were investigated. Geometric parameters and vibrational frequencies of these structural units were calculated. The quantum chemical calculations were followed by normal coordinate analysis. Based on the yielded results, the vibrational spectra of the clusters were simulated. The results for germanium sulfide and germanium selenide were compared. It was concluded that in the spectral regions where germanium sulfide is not applicable for fiber optics, germanium selenide or different germanium sulfide–selenides are suitable to replace it. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

过渡金属类立方烷型簇合物合成中的“活性元件组装”设想

本文讨论了Roussin黑盐的形成机理和“G”系模型物结构及其固氮活性成因的化学和量子化学研究结果。并由此提出了过渡金属类立方烷型簇合物合成中的“活性元件组装”设想;即过渡金属原子簇,特别是含μ2和μ3桥的类立方烷簇,可能由构成该原子簇的基本结构“元件”在一定活化条件下组装而成。考察了现有的Fe-S,Mo-S,Mo-Fe-S以及一些M-M′-X构型相类似的类立方烷簇合物,如[Fe_4S_4(SR)_4]~(2-),[MoFe_3S_4(SR)_n]~(m-),[VFe_3S_4Cl_3(DMF)3]单类立方烷簇,[Mo_2Fe_6S_9(SR)_8]~(8-),[Mo_2Fe_6S_8(SR)_9]~(3-),[Mo_2Fe_7S_8(SR)_(12)]~(3-,4-)桥联双立方烷簇以及(MeZn)_6Zn(OMe)_8孪合双立方烷簇的自兜合成反应,发现尽管它们似乎都是由简单的无机盐和有机配体“自兜”而成,然而它们都不能不经过某些“元件组装”的过程。提出了它们的可能的“元件组装”途径。此外还讨论了“元件组装在其他合成Mo、Fe、S类立方烷簇的反应中的存在。最后还进一步探讨了其他类型簇合物合成反应情况,表明“元件组装”设想是可能推广到类立方烷型簇以外的其他一些原子簇的合成的。     

Molybdenum-iron-sulfur clusters of nuclearities eight and sixteen, including a topological analogue of the P-cluster of nitrogenase

Transformations of the edge-bridged double cubane cluster [(Cl4cat)2(Et3P)2Mo2Fe6S8(PEt3)4] (1) under reducing conditions have been investigated as synthetic approaches to the clusters of nitrogenase. Cluster 1 is a versatile precursor to different Mo-Fe-S cluster types. The reaction system 1/K(C14H10) in THF yields the reduced cluster [(Cl4cat)2(Et3P)2Mo2Fe6S8(PEt3)4]1- (2), which as its crystalline Et4N+ salt retains the edge-bridged structure of 1. X-ray structural and M?ssbauer spectroscopic results indicate an unsymmetrical electron distribution with localized [MoFe3S4]2+,1+ cubane-type units. The system 1/2K(C14H10)/2HS- in THF/acetonitrile affords [(Cl4cat)4(Et3P)4Mo4Fe12S20K3(DMF)]5- (3), whose structure was determined as the Ph3PMe+ salt. The cluster consists of two isostructural Mo2Fe6S9 fragments connected by two mu 2-S bridges. Three potassium ions are bound between the two fragments. In each fragment, the iron atoms are present in tetrahedral FeS4 and the molybdenum atoms in octahedral MoO2PS3 coordination units, and two MoFe3(mu 3-S)3 cuboidal units are bridged by a common mu 6-S atom. The fragments have idealized mirror symmetry and are isostructural with two of the fragments present in the previously reported high-nuclearity cluster [(Cl4cat)6(Et3P)6Mo6Fe20S30]8- (4) (Osterloh, F.; Sanakis, Y.; Staples, R. J.; Münck, E.; Holm, R. H. Angew. Chem., Int. Ed. Engl. 1999, 38, 2066). On the basis of overall shape, atom connectivities, and metric features, the Mo2Fe6S9 fragment is a topological analogue of the P-cluster of nitrogenase in the PN (reduced) state. A third cluster type, formed as a minor byproduct in the reaction system leading to 2, was crystallographically identified as [(Cl4cat)2(Et3P)2Mo2Fe6S8(PEt3)4]4-, whose core is made up of two MoFe3(mu 3-S)3 cuboidal units bridged by two mu 2-S atoms and connected by a direct Fe-Fe bond. Full structural details and the redox properties of 2 and 3 are reported.     

Experimental evidence of structural transition from fcc to bulk bcc in nanophase metal clusters of (Fe)n, (Cr)n, (Mo)n and (W)n produced by CO2 laser multiphoton decomposition of metal carbonyls

We have produced nanophase metal clusters, (Fe)_n, (Cr)_n, (Mo)_n and (W)_n, by multiphoton decomposition of the corresponding metal carbonyls with a 10.6 μm CO₂ laser in the presence of Ar and SF₆. The size distribution was narrow and the average diameter was 6, 3.5, 2 and 1 nm for Fe, Cr, Mo and W clusters, respectively. The structure was found to be bcc for both Fe and Cr clusters, fcc for Mo clusters, and amorphous for W clusters (note that all the bulk metals have bcc structure). Considering the cluster sizes (9630, 1870, 230 and 30 for Fe, Cr, Mo and W clusters, respectively) estimated from their average diameters, it is likely that there exists a structural transition from fcc to bulk bcc with increasing cluster size in these metal clusters.     

原子簇NixFe和NiFex(x=1-5)电子性质的DFT研究

More than one hundred models were designed to reflect the local structure and electronic property of Ni-Fe amorphous alloys. After calculating by DFF method, a series of configurations of clusters NixFe and NiFex （x = 1 - 5） were gained. The configurations, which possessed the lowest energies and non-imaginary frequencies, were considered the most stable optimized structures. The catalytic activity, charge and magnetic properties were analyzed and discussed. The different Fe content changed the catalytic properties of clusters through altering the value of Fermi level of every cluster. However the density of state （DOS） nearby Fermi level and average 3d orbital population of atom Ni, which were also important properties related to the catalytic activation, were little changed. Based on the Fermi level, the activity of catalyst toward hydrogenation reaction would be considered best when the ratio of Ni to Fe was close to 1. The Fermi level of clusters was far distant to the level of nitrogen in singlet state. It would be the reason why the reaction condition in ammonia synthesis and nitrogen fixation process was rigorous. When Fe atom contents were higher than 75% （NiFe3）, the electrons transferred from atom Fe to Ni, but when the ratio was decreased, the transfer was reversed. The ratio of atoms of local structure also played an important role in the aspect of electron transition. On the average 3d orbital population of atom Fe, the average magnetic moments of Fe atoms in clusters were calculated. When Fe atom contents were 50% nearly, the average magnetic moment achieved the highest point.     

Dynamics of an [Fe4S4(SPh)4]2- cluster explored via IR, Raman, and nuclear resonance vibrational spectroscopy (NRVS)-analysis using 36S substitution, DFT calculations, and empirical force fields

We have used four vibrational spectroscopies--FT-IR, FT-Raman, resonance Raman, and 57Fe nuclear resonance vibrational spectroscopy (NRVS)--to study the normal modes of the Fe-S cluster in [(n-Bu)4N]2[Fe4S4(SPh)4]. This [Fe4S4(SR)4]2- complex serves as a model for the clusters in 4Fe ferredoxins and high-potential iron proteins (HiPIPs). The IR spectra exhibited differences above and below the 243 K phase transition. Significant shifts with 36S substitution into the bridging S positions were also observed. The NRVS results were in good agreement with the low temperature data from the conventional spectroscopies.The NRVS spectra were interpreted by normal mode analysis using optimized Urey-Bradley force fields (UBFF) as well as from DFT theory. For the UBFF calculations, the parameters were refined by comparing calculated and observed NRVS frequencies and intensities. The frequency shifts after 36S substitution were used as an additional constraint. A D 2d symmetry Fe4S4S'4 model could explain most of the observed frequencies, but a better match to the observed intensities was obtained when the ligand aromatic rings were included for a D 2d Fe4S4(SPh)4 model. The best results were obtained using the low temperature structure without symmetry constraints. In addition to stretching and bending vibrations, low frequency modes between approximately 50 and 100 cm(-1) were observed. These modes, which have not been seen before, are interpreted as twisting motions with opposing sides of the cube rotating in opposite directions. In contrast with a recent paper on a related Fe4S4 cluster, we find no need to assign a large fraction of the low frequency NRVS intensity to 'rotational lattice modes'. We also reassign the 430 cm(-1) band as primarily an elongation of the thiophenolate ring, with approximately 10% terminal Fe-S stretch character. This study illustrates the benefits of combining NRVS with conventional Raman and IR analysis for characterization of Fe-S centers. DFT theory is shown to provide remarkable agreement with the experimental NRVS data. These results provide a reference point for the analysis of more complex Fe-S clusters in proteins.     

Models of molecular structures of aluminum–iron clusters AlFe<Subscript>3</Subscript>, Al<Subscript>2</Subscript>Fe<Subscript>3</Subscript>, and Al<Subscript>2</Subscript>Fe<Subscript>4</Subscript> according to quantum-chemical DFT calculations

The geometrical parameters of molecular structures of three types of aluminum–iron clusters containing in total four, five, and six Al and Fe atoms in structural units have been calculated by the OPBE/TZVP density functional theory (DFT) method with the Gaussian09 program package. It has been found that the AlFe₃, Al₂Fe₃, and Al₂Fe₄ clusters can have four, eight, and nine structural modifications, which significantly differ in stability and geometric parameters. Bond lengths and bond and torsion (dihedral) angles are reported for each of these modifications.     

Gas-phase IR spectroscopy of anionic iron carbonyl clusters

The first gas-phase vibrational spectra are presented for several anionic iron carbonyl clusters, ranging in size from Fe(CO)4- to Fe5(CO)14- in the CO-stretching region (1600-2100 cm-1). The experimental spectra provide some immediate structural information about the clusters in the form of low-wavenumber (1750-1850 cm-1) bands marking the presence of bridging carbonyl ligands (mu2-COs). Supporting DFT calculations are presented for the smaller clusters (<3 Fe atoms) and give good agreement with the experimental data, allowing structural assignments for these cases. The Fe2(CO)7- spectrum suggests a structure lacking bridging carbonyl ligands, in agreement with the DFT results. For the case of Fe2(CO)8-, there are two possible structures based on the calculations, both with and without bridging carbonyls. The presence of a low-frequency band ( approximately 1770 cm-1) in the experimental spectrum conclusively demonstrates the existence of the bridged form. The ramifications of these data for metal-metal bonding in the clusters are also considered.     

Normal-mode analysis of FeCl4- and Fe2S2Cl42- via vibrational mössbauer, resonance Raman, and FT-IR spectroscopies

[NEt(4)][FeCl(4)], [P(C(6)H(5))(4)][FeCl(4)], and [NEt(4)](2)[Fe(2)S(2)Cl(4)] have been examined using (57)Fe nuclear resonance vibrational spectroscopy (NRVS). These complexes serve as simple models for Fe-S clusters in metalloproteins. The (57)Fe partial vibrational density of states (PVDOS) spectra were interpreted by computation of the normal modes assuming Urey-Bradley force fields, using additional information from infrared and Raman spectra. Previously published force constants were used as initial values; the new constraints from NRVS frequencies and amplitudes were then used to refine the force field parameters in a nonlinear least-squares analysis. The normal-mode calculations were able to quantitatively reproduce both the frequencies and the amplitudes of the intramolecular-mode (57)Fe PVDOS. The optimized force constants for bending, stretching, and nonbonded interactions agree well with previously reported values. In addition, the NRVS technique also allowed clear observation of anion-cation lattice modes below 100 cm(-1) that are nontrivial to observe by conventional spectroscopies. These features were successfully reproduced, either by assuming whole-body motions of point-mass anions and cations or by simulations using all of the atoms in the unit cell. The advantages of a combined NRVS, Raman, and IR approach to characterization of Fe-S complexes are discussed.     

Structure of Bromotrinitrosyl Iron, [Fe(NO)3Br], and DFT Calculations of the Structures of [Fe(NO)3X] (X = Cl,Br, I)

Bromotrinitrosyl iron was prepared by passing a stream of nitrogen monoxide over a mixture of iron dibromide and iron powder at elevated temperatures. It readily loses NO to give [(ON)₂Fe(μ‐Br)Fe(CO)₂]. The structure of freshly obtained [Fe(NO)₃Br] was determined by X‐ray diffraction at 200 K and shows (distorted) tetrahedral coordination with N–Fe–N and N–Fe–Br angles of 107.9(2)° and 111.0(2)° and bent Fe–N–O groups (162.5(6)°). The DFT calculations in the series [Fe(NO)₃X] (X = Cl, Br, I) reproduce well the experimental structural parameters and vibrational frequencies.     

Modeling structures and vibrational frequencies for dinitrosyl iron complexes (DNICs) with density functional theory

The biochemical and physiological importance of nitric oxide (NO) in signaling and vasodilation has been studied for several decades. The discovery of both protein-bound and free low molecular weight dinitrosyl iron complexes (DNICs) suggests that such compounds might play roles in biological NO storage and transport. These complexes have important distinguishing spectroscopic features, including EPR and M?ssbauer spectra, and NO vibrational frequencies (ν((NO))). The latter are particularly sensitive to modifications of the ligand environment and metal oxidation states. Examinations of functionals and basis sets delineate their effect on the NO vibrational frequencies and allow development of a methodology to calculate these frequencies in other DNICs. Three complexes of the form (L)(CO)Fe(NO)(2) (L = CO, N,N'-dimethyl-imidazol-2-ylidene (IMe) or 1-methylimidazole (MeImid)), where {Fe(NO)(2)}(10) is in its reduced form, have been used to calibrate the vibrational frequencies. The functional BP86 paired with a basis set of SDD/ECP on the metal and 6-311++G(d,p) on the ligand atoms exhibits the most accurate results, with deviations from experimental vibrational frequencies of no more than ±40 cm(-1). Subsequent investigations were performed on a series of diiron trinitrosyl complexes of the form {Fe(NO)}(7)-{Fe(NO)(2)}(9) bridged by sulfurs, namely, [(ON)Fe(μ-S,S-C(6)H(4))(2)Fe(NO)(2)](-), [Fe(NO)(2){Fe(NS(3))(NO)}-μ-S,S'], and [(ON)Fe(bme-dach)Fe(NO)(2)-μ-S,S'](+), with the ideal functional/basis set pair determined via the aforementioned test set. The ground state energetics (singlet/triplet/singlet, respectively), geometric parameters, and nitrosyl vibrational frequencies were calculated. The results for the former two complexes correlated well with the experimental work, and in contrast with what was reported in an earlier computational study, a stable triplet ground state structure was optimized for [Fe(NO)(2){Fe(NS(3))(NO)}-μ-S,S']. For [(ON)Fe(bme-dach)Fe(NO)(2)-μ-S,S'](+), whose synthesis and structure were recently reported, the geometric parameters, vibrational frequencies, and total energies compare well to experimental ones and favor a singlet ground state.     

金属羰基化合物的结构对氧原子转移反应速率的影响

本文研究了氧化三甲胺Ｍｅ３ＮＯ与羰基簇合物Ｍ４（ＣＯ）１２－ｎＬｎ（Ｍ＝Ｃｏ，Ｉｒ；ｎ＝１，２；Ｌ＝磷配体）的氧转移反应动力学，讨论了反应机理。反应符合二级速率方程：ｒ＝Ｋ２［Ｍｅ３ＮＯ］［Ｍ４（ＣＯ）１２－ｎＬｎ］Ｍ４（ＣＯ）１２－ｎＬｎ的氧转移反应活性呈现如下顺序：中心元素不同时Ｃｏ４（ＣＯ）１２－ｎＬｎ＜Ｉｒ４（ＣＯ）１２－ｎＬｎ；取代配体不同时Ｍ４（ＣＯ）１２－ｎ（Ｐ（ＯＭｅ）３）ｎ＞Ｍ４     

Deciphering Iron‐Dependent Activity in Oxygen Evolution Catalyzed by Nickel–Iron Layered Double Hydroxide

Nickel iron oxyhydroxide is the benchmark catalyst for the oxygen evolution reaction (OER) in alkaline medium. Whereas the presence of Fe ions is essential to the high activity, the functions of Fe are currently under debate. Using oxygen isotope labeling and operando Raman spectroscopic experiments, we obtain turnover frequencies (TOFs) of both Ni and Fe sites for a series of Ni and NiFe layered double hydroxides (LDHs), which are structurally defined samples of the corresponding oxyhydroxides. The Fe sites have TOFs 20–200 times higher than the Ni sites such that at an Fe content of 4.7 % and above the Fe sites dominate the catalysis. Higher Fe contents lead to larger structural disorder of the NiOOH host. A volcano‐type correlation was found between the TOFs of Fe sites and the structural disorder of NiOOH. Our work elucidates the origin of the Fe‐dependent activity of NiFe LDH, and suggests structural ordering as a strategy to improve OER catalysts.