On the electronic structure of giant polyoxometalates: Mo(132)vs. W(72)Mo(60)

The molecular and electronic structure of the spherical Keplerates [{(Mo(VI))Mo(VI)(5)O(21)}(12)(Mo(V)(2)O(4))(30)](12-) (Mo(132)) and [{(W(VI))W(VI)(5)O(21)}(12)(Mo(V)(2)O(4))(30)](12-) (W(72)Mo(60)) has been determined, for the first time, using first-principles density functional theory (DFT) based methods including solvent effects. Computed geometric parameters are in very good agreement with X-ray data, whereas the electronic structure reveals the archetypal nature of polyoxometalates.     

Radiochromatography of some99Mo(V) and99Mo(VI) polyaminocarboxylic acids

A simple, rapid and inexpensive ascending thin-layer and paper radiochromatographic procedure is described, which can be used in the separation and possible identification of some⁹⁹Mo(V) and⁹⁹Mo(VI) polyaminocarboxylic acid chelates.     

MTi(0.7)Mo(0.3)Mo(5)O(10) (M = SR, Eu), first evidence of mono- and bicapped bioctahedral Mo(11) and Mo(12) clusters: synthesis, crystal structures, and physical properties

The novel quaternary reduced molybdenum oxides MTi(0.7)Mo(0.3)Mo(5)O(10) (M = Sr, Eu) have been synthesized by solid-state reaction at 1400 degrees C for 48 h in sealed molybdenum crucibles. Their crystal structures were determined on single crystals by X-ray diffraction. Both compounds crystallize in the orthorhombic space group Pbca with 8 formula units per cell and the following lattice parameters: a(Sr) = 9.1085 (7), b(Sr) = 11.418 (1), and c(Sr) = 15.092 (3) A; a(Eu) = 9.1069 (7), b(Eu) = 11.421 (2), and c(Eu) = 15.075 (1) A. The Mo network is dominated by bioctahedral Mo(10) clusters, which coexist randomly with Mo(11) and Mo(12) clusters (monocapped and bicapped Mo(10) clusters). The Mo-Mo distances within the clusters range from 2.62 to 2.92 A and the Mo-O distances from 1.99 to 2.17 A as usually observed in the reduced molybdenum oxides. The Sr(2+) and Eu(2+) ions occupy large cavities, which result from the fusion of two cubooctahedra and thus are surrounded by 11 oxygen atoms. The M-O distances range from 2.50 to 3.23 A for the Sr compound and from 2.49 to 3.24 A for the Eu analogue. Single-crystal resistivity measurements indicate that both materials are poor metals with transitions to semiconducting states below 50 and 40 K and room temperature resistivity values of 9 x 10(-3) and 5 x 10(-3) Omega.cm for the Sr and Eu compounds, respectively. The magnetic susceptibility data indicate paramagnetic behavior due to the Eu(2+) moment at high temperatures for the Eu compound and do not reveal the existence of localized moments on the Mo and Ti sublattice in the Sr compound. An XPS study clearly suggests that the isolated Ti ions are tetravalent. Theoretical considerations preclude the existence of heterometallic Mo-Ti clusters.     

钼(钨)-钼-硫簇合物的~(95)Mo NMR研究

对含有[MS4]2-（M＝Mo，W）单元的一系列钼（钨）-钼-硫簇合物进行了95MoNMR研究，定性分析了95Mo化学位移随金属原子配位数、配位金属种类和配位金属配体改变而变化的规律。结果表明，随着[MoS4]2-配位金属原子数的增加，[MoS4]2-上Mo的化学位移逐渐向高场移动，这可归因于低氧化态MO0上的电子通过硫桥离域到高氧化态的Mo上。为了解析Mo0上化学位移的实验结果，采用MM＋力场对[（OC）4MOS2MoS2]2-和[｛（OC）4Mo｝MoS4]2-的晶体结构进行几何优化，使之更接近于溶液中的结构，然后利用Fenske－Hall方法计算Mo原子上的净电荷分布，计算结果较好地好择了Mo和Mo0化学位移的变化趋势。     

Diphenylamino-fluorphosphin-carbonyl-Komplexe von Ni(0) und Mo(0)

Diphenylamino-fluorphosphine-carbonyl Complexes of Ni(0) and Mo(0) The complexes Ni(CO)_x[(Ph₂N)_yPF_3–y]_4–x (x₁ = 1–3, y₁ = 1; x₂ = 1–2, y₂ = 2) are prepared by reaction of Ni(CO)₄, i. e. norbornadiene-molybdenum(0)-tetracarbonyl with diphenylamino-fluorphosphines. The chemical properties, n.m.r. and i.r. spectra are discussed.     

Die Kristallstruktur des Komplexnitrides Mo(Ta,Mo)2N2

In the ternary system Ta/Mo/N a complex nitride of formula Mo(Ta,Mo)₂N₂ was observed at a nitrogen pressure of 360 bar and a temperature of 1,600°C. The crystal structure was determined from X-ray powder diagrams. The tetragonal unit cell, space groupI4/mmm-D _4h ¹⁷ , lattice parametersa=0.3051 nm,c=1.2530 nm contains ten atoms with an arrangement of the metal atoms corresponding to the MoSi₂-Type structure.

     

Thermal homolytic fission of the MoMo bond in (h5 -C5H5)2Mo2(CO)6

Kinetic studies of reactions of the MoMo bonded complex (h⁵-C₅H₅)₂Mo₂(CO)₆ in decalin show that it undergoes reversible homolytic fission and that the activation enthalpy required to break the MoMo bond is 135.9 ± 2.2 kJ mol^?1.     

Solvent extraction of Mo(V) and Mo(VI) from hydrochloric acid into Aliquat 336 chloroform solution

Solvent extraction of macro amounts of Mo(V) and Mo(VI) from HCl using Aliquat 336 in chloroform was performed for the electrochemistry of Sg. The extraction reaction attained equilibrium with a shaking time of 10 s in higher than 8 M HCl. The D values of Mo(V) obtained by the electrochemical reduction of Mo(VI) were in good agreement with those obtained by the extraction of MoCl₅, and the D values of Mo(V) were higher than those of Mo(VI). These results suggested that the reduction behavior of Sg might be studied by electrochemical reduction combined with the present solvent extraction.     

Efficient epoxidation of terminal and internal alkenes using t-butylhydroperoxide catalysed by polybenzimidazole-supported Mo(VI).(PBI.Mo)

A polybenzimidazole-supported Mo complex (PBI.Mo) has been prepared by a method already reported. Extensive investigation of digestion procedures has shown a dry-ashing method using NaNO₃/HNO₃ (conc.) at 560°C to be an optimal method for preparing samples for Mo analysis by atomic absorption spectrophotometric methodology. Mo loadings in the range 1.32–0.62 mmol Mo g⁻¹ polymer were demonstrated. PBI.Mo has been used as a heterogeneous catalyst in the epoxidation of cyclohexene, methylene-cyclohexane, 4-vinyl cyclohexene, styrene, 1,3-pentadiene and allyl chloride, bromide and alcohol using t-butylhydroperoxide as the oxidant. The catalyst is very effective for the first four substrates, somewhat less active than soluble MoO₂acac₂, but providing final yields and purity of products generally better than using MoO₂acac₂. The 1,3-pentadiene displays an overall conversion of ∼35% with a distribution of the four possible monoepoxide isomers similar to that obtained with MoO₂acac₂ as catalyst. The allylic substrates showed poor conversion probably as a result of secondary (oligomerisation) reactions involving the epoxide products. Running the epoxidations for extended periods in air allows in situ generation of alkyl hydroperoxides in the case of cyclohexene and 4-vinylcyclohexene and these are then effective internal oxidants for further Mo catalysed epoxidation of these alkenes. When run under anaerobic conditions the reactions are very clean with no evidence of any free radical processes contributing. In all cases Mo leaching is minimal. Good activity is seen in the recycling of PBI.Mo in the case of styrene and 1,3-pentadiene, although with cyclohexene and 4-vinylcyclohexene steady deactivation is seen, probably as a result of catalyst fouling. Thermogravimetric analyses suggest that it might be possible to burn off the foulant without destroying the catalyst.     

Structure, formation, and dynamics of Mo(12) and Mo(16) oxothiomolybdenum rings containing terephtalate derivatives

The influence of rigid or semirigid dicarboxylate anions, terephtalate (TerP(2-)), isophtalate (IsoP(2-)), and phenylenediacetate (PDA(2-)) on the self-condensation process of the [Mo(2)O(2)S(2)](2+) dioxothio cation has been investigated. Three new molybdenum rings, [Mo(12)O(12)S(12)(OH)(12)(TerP)](2-) ([Mo(12)TerP](2-)), [Mo(16)O(16)S(16)(OH)(16)(H(2)O)(4)(PDA)(2)](4-) ([Mo(16)(PDA)(2)](4-)), and [Mo(16)O(16)S(16)(OH)(16)(H(2)O)(2)(IsoP)(2)](4-) ([Mo(16)(IsoP)(2)](4-)) have been isolated and unambiguously characterized in the solid state by single-crystal X-ray studies and in solution by various NMR methods and especially by diffusion-correlated NMR ((1)H DOSY) spectroscopy, which was shown to be a powerful tool for the characterization and speciation of templated molybdenum ring systems in solution. Characterization by FT-IR and elemental analysis are also reported. The dynamic and thermodynamic properties of both the sixteen-membered rings were studied in aqueous medium. Specific and distinct behaviors were revealed for each system. The IsoP(2-)/[Mo(2)O(2)S(2)](2+) system gave rise to equilibrium, involving mono-templated [Mo(12)IsoP](2-) and bis-templated [Mo(16)(IsoP)(2)](4-) ions. Thermodynamic parameters have been determined and showed that the driving-force for the formation of the [Mo(16)(IsoP)(2)](4-) is entropically governed. However, whatever the conditions (temperature, proportion of reactants), the PDA(2-)/[Mo(2)O(2)S(2)](2+) system led only to a single compound, the [Mo(16)(PDA)(2)](4-) ion. The latter exhibits dynamic behavior, consistent with the gliding of both the stacked aromatic groups. Stability and dynamics of both Mo(16) rings was related to weak hydrophobic or pi-pi stacking inter-template interactions and inner hydrogen-bond network occurring within the [Mo(16)(IsoP)(2)](4-) and [Mo(16)(PDA)(2)](4-) ions.     

Mo(W)-Cu(Ag)-S原子簇化合物的研究现状

本文在研究Ｍｏ（Ｗ）－Ｃｕ（Ａｇ）－Ｓ原子簇化合物的低热固态合成化学基础上，详细地对该类簇合物进行了归纳，从中提出；１，ＭＯ４－ｎＳｎ＾２＾－（Ｍ＝Ｍｏ，Ｗ；ｎ＝２，３，４）作为配体中心。２，氧原子在簇合物中仅作为端基，不参与同其他金属成键。３，单个ＭＳ４（Ｍ＝Ｍｏ，Ｗ）基团最多只能键合六个Ｃｕ（Ａｇ）原子，即最大核数为七。４，迄今为止所有Ｍｏ（Ｗ）－Ｃｕ－Ｓ原子簇化合物中Ｃｕ均为＋１价。５，预计     

Mo（W）－Cu（Ag）－S原子簇化合物的研究现状

本文在研究Ｍｏ（Ｗ）－Ｃｕ（Ａｇ）－Ｓ原子簇化合物的低热固态合成化学基础上，详细地对该类簇合物进行了归纳，从中提出：１．（Ｍ＝Ｍｏ，Ｗ；ｎ＝２，３，４）作为配体中心．２．氧原子在簇合物中仅作为端基，不参与同其他金属成键．３．单个ＭＳ４（Ｍ＝Ｍｏ，Ｗ）基团最多只能键合六个Ｃｕ（Ａｇ）原子，即最大核数为七．４．迄今为止所有Ｍｏ（Ｗ）－Ｃｕ－Ｓ原子簇化合物中Ｃｕ均为＋１价．５．预计合低价态Ｍｏ（Ｗ）的这类簇合物将会有很大进展．     

Einfache Darstellungsmethoden des einzigen bekannten Perthiometallats [(S2)2 Mo(S2)2Mo(S2)2]2−. Zur Kenntnis der Einheit {Mo2(S2)2}6+

Simple Preparation Methods of the Only Known Perthiometallate [(S₂)₂(Mo)S₂)₂ Mo(S₂)₂]^2? · On the Moiety {Mo₂(S₂)₂}⁶⁺ Different aspects of the preparation of the only known perthiometallate [(S₂)₂Mo(S₂)₂Mo(S₂)₂]^2? (a compound with the unusual coordination number (9) have been discussed. Simple preparation methods could be developed. A discussion of the properties of the stabilising central moiety {Mo(S₂)₂}⁶⁺ containing a metal-metal bond follows.     

Low-temperature reduction of NO(2) on oxidized Mo(110)

The reactions of nitrogen dioxide (NO(2)) were investigated on oxidized Mo(110) containing both chemisorbed oxygen and a thin film oxide. NO(2) reacts on both oxidized Mo(110) surfaces via a combination of reversible adsorption and reduction to NO, N(2), and trace amounts of N(2)O below 200 K. On the surface containing chemisorbed O, there is some complete dissociation of NO(2) to yield N(a) and O(a). N(2) forms at high temperatures through atom combination. On both surfaces, NO is the predominant product of NO(2) reduction. However, the chemisorbed layer which has a low oxidation state, and hence a greater capacity to accept oxygen, more effectively reduces NO(2). The selectivity for N(2) formation over N(2)O is greater for NO(2) as compared with NO on both surfaces studied. The selectivity changes are largely attributed to an increase in the concentration of Mo=O species and a change in the distribution of oxygen on the surface. Notably, more oxygen, in particular Mo=O moieties, is deposited by NO(2) reaction than by O(2) reaction, indicating that NO(2) is a stronger oxidant. The fact that there are several N-containing species on the surface at low temperatures may also affect the product distribution. On both surfaces, N(2)O(4), NO(2), and NO are identified by infrared spectroscopy upon adsorption at 100 K. All N(2)O(4) desorbs by 200 K, leaving only NO(2) and NO on the surface. Infrared spectroscopy of NO(2) on (18)O-labeled surfaces provides evidence for oxygen transfer or exchange between different types of sites even at low temperatures.     

Fullerene-like (IF) Nb(x)Mo(1-x)S2 nanoparticles

IF-Mo1-xNbxS2 nanoparticles have been synthesized by a vapor-phase reaction involving the respective metal halides with H2S. The IF-Mo1-xNbxS2 nanoparticles, containing up to 25% Nb, were characterized by a variety of experimental techniques. Analysis of the powder X-ray powder diffraction, X-ray photoelectron spectroscopy, and different electron microscopy techniques shows that the majority of the Nb atoms are organized as nanosheets of NbS2 within the MoS2 host lattice. Most of the remaining Nb atoms (3%) are interspersed individually and randomly in the MoS2 host lattice. Very few Nb atoms, if any, are intercalated between the MoS2 layers. A sub-nanometer film of niobium oxide seems to encoat the majority of the nanoparticles. X-ray photoelectron spectroscopy in the chemically resolved electrical measurement mode (CREM) and scanning probe microscopy measurements of individual nanoparticles show that the mixed IF nanoparticles are metallic independent of the substitution pattern of the Nb atoms in the lattice of MoS2 (whereas unsubstituted IF-MoS2 nanoparticles are semiconducting). Furthermore the IF-Mo1-xNbxS2 nanoparticles are found to exhibit interesting single electron tunneling effects at low temperatures.