Solid-state synthesis of molybdenum and tungsten porphyrins and aerial oxidation of coordinated benzenethiolate to benzenesulfonate

A new route is developed for the synthesis of molybdenum and tungsten porphyrins using [M(NO)(2)py(2)Cl(2)] (M = Mo, W) as the metal source and TPP (dianion of 5,10,15,20-meso-tetraphenylporphyrin) in the benzoic acid melt. Complexes [Mo(V)O(TPP)(OOCPh)] (1) and [W(V)O(TPP)(OOCPh)] (2) are isolated in almost quantitative yield. These are characterized by single-crystal X-ray structure analysis, electron paramagnetic resonance, electronic and IR spectroscopy, and magnetic moment measurements. Benzenethiol substitutes for PhCOO(-) in 1, forming an intermediate thiolato complex that responds to the intramolecular redox reaction across the Mo(V)-SPh bond to yield [Mo(IV)O(TPP)] (3). Under an excess of benzenethiol, PhS(-) is coordinated to the vacant site in 3, which under aerial oxidation is oxidized to benzenesulfonate to form [Mo(V)O(TPP)(O(3)SPh)] (4). 2 undergoes similar aerial oxidation chemistry albeit slowly.     

Molecular precursor route to bulk and silica-supported Nb2Mo3O14 using water-soluble oxo-oxalato complexes

The catalytically relevant Nb2Mo3O14 phase has been prepared in bulk and silica-supported forms via the so-called "multiple molecular precursors method" from water-soluble oxo-oxalato complexes of Nb and Mo, (NH4)3[NbO(ox)3].H2O, and (NH4)2[MoO3(ox)].H2O. Thermal treatment of the mixed Nb-Mo precursor has been optimized for the formation of the pure Nb2Mo3O14 phase, either as bulk oxide or a silica-supported phase with high specific surface area. A characterization of the bulk phase obtained via the conventional ceramic route has also been carried out and a comparison has been made with the precursors route. According to this route, the Nb2Mo3O14 phase is shown to be formed in a pure form at 700 degrees C (i.e., 100 degrees C below the lowest temperature reported so far for the formation of the phase by the ceramic method). The supported samples have appreciable specific surface areas of 60-70 m(2) g(-1), much larger than those reached in the previous attempts under vacuum in sealed vials. The SEM and EDX analyses reveal a high dispersion of the desired phase on the silica support.     

Novel mixed-valence heteropolyoxometalates: a molybdenum diphosphonate anion [MoV7MoVIO16(O3PPhPO3H)4]3- and its one- and two-dimensional assemblies

A novel mixed-valence polyoxomolybdenum anion, [Mo(V)(7)Mo(VI)O(16)(O(3)PPhPO(3)H)(4)](3)(-), was synthesized hydrothermally from molybdenum oxide, molybdenum metal, boric and phosphoric acids, 1,2-phenyldiphosphonic acid, and imidazole (ImH) and was structurally characterized as an imidazolium salt (orthorhombic, Aba2; a = 16.674(4), b = 17.238(1), and c = 24.81(2) A). One- and two-dimensional structures of this anion and additional molybdenum diphosphonate linkers were assembled as well. They were structurally characterized as their pyridinium (pyH) salts (pyH)(4)[[Mo(V)(7)Mo(VI)O(16)(O(3)PPhPO(3))(2)(O(3)PPhPO(3)H)(2)][Mo(2)O(4)(OH)(HO(3)PPhPO(3)H)]].5H(2)O (monoclinic, P2(1)/c; a = 20.8506(9), b = 22.866(1), and c = 21.1403(9) A; beta = 118.7087(8) degrees ) and (pyH)(3)[[Mo(V)(7)Mo(VI)O(16)(O(3)PPhPO(3))(4)][Mo(2)O(2)(OH)(2)(HO(3)PPhPO(3)H)]].3H(2)O (orthorhombic, Pca2(1); a = 19.057(1), b = 20.402(2), and c = 20.660(2) A). The compounds were also characterized by IR spectroscopy and magnetic measurements.     

Synthesis,Crystal Structure of Cis—dioxo—catecholatotungsten（VI） Complex and Its NMR Studies on the Interaction with ATP

Cis-dioxo-catecholatotungsten(VI) complex anion[W^(VI)O2-(OC6H4O)2]^2- was obtained with discrete protonated ethylenediamine (NH2CH2CH2NH3)^ cations by the reaction of tetrabutyl ammonium decatungstate with catechol in the mixed solvent of CH3OH,CH3CN and ethylenediamine,and compared with its molybdenum anaogue [Mo^(V) O2(OC6H4O)2]^3- by crystal structure,UV,EPR,The results of the UV and EPR spectra show that tungsten is less redox active than molybdenum since the molybdenum is reduced from Mo(VI) to Mo(V) but tungsten stays in the original highest oxidized state Mo(VI) when they are crystallized from the solution above.It is worthy to note that [W^(VI)O2(OC6H4O)]^2- shows the same coordination structure as its molybdenum analogue in which the metal center exhibits distorted octahedral coordination geometry with two cis-dioxocatecholate ligands and might have the related coordination structure feature with the cofactor of flavoenzyme because [Mo^(V)O2(OC6H4O)2]^3- presented essentially the same EPR spectra as flavoenzyme.The NMR studies on the interaction of the title complex with ATP reveal that the reduction of W(VI) to W(V) occurs when the title complex is dissolved in D2O and the W(V) is oxidized again when ATP solution is mixed with original solution and the hydrolysis of the catecholato ligand take places at mean time being monitored by ^1H NMR and ^13C NMR spectra.     

Synthesis of heterometallic bismuth/molydenum alkoxides and their behavior on silica surfaces

The reaction of [(C(3)H(5))Mo(CO)(2)(CH(3)CN)(2)Cl], 2, with [Bi(OCH(2)CH(2)OCH(3))(3)](2) on a large scale leads to the novel molybdenum/bismuth alkoxide [(C(3)H(5))Mo(CO)(2)(mu-kappa O,2 kappa O'-OCH(2)CH(2)OCH(3))(2)(mu-kappa O-OCH(2)CH(2)OCH(3))BiCl], 6, as the main product as well as to [(C(3)H(5))Mo(CO)(2)(mu-kappa O,2 kappa O'-OCH(2)CH(2)OCH(3))(2)(mu-Cl)BiCl], 4, as a byproduct. Both compounds were characterized by elemental analysis, IR, and NMR spectroscopy as well as by X-ray diffraction. If 6 is brought into contact with a large excess of silica gel, aggregation and condensation reactions are initiated, which led to clusters of ca. 200 nm size spread over the silica surface. When the resulting material is calcinated at 350 degrees C in the presence of O(2), all organic ligands are eliminated and the metal oxo units rearrange: SEM/EDX measurements showed afterward Mo-free bismuth oxo clusters with sizes between 30 and 1000 nm, which are distributed together with molybdenum oxo particles of lower nuclearity over the silica surface. If such a material is employed as a potential catalyst for the propene oxidation under technical conditions, no activity is observed. If, however, the process is performed under very low pressures, a conversion of 5% is found. This result is discussed in the context of the mechanism proposed for the technical oxidation of propene to acrolein on bismuthmolybdate catalysts.     

钾修饰的moo3/sio2催化剂的xrd和tpr表征

moo3/k2o/sio2催化剂;xrd;tpr;高硫合成气;甲硫醇     

Syntheses, crystal structures, magnetic and luminescent properties of two classes of molybdenum(VI) rich quaternary lanthanide selenites

Hydrothermal reactions of lanthanide(III) oxide, molybdenum oxide, and SeO(2) at 230 °C lead to five new molybdenum-rich quaternary lanthanide selenites with two types of structures, namely, H(3)Ln(4)Mo(9.5)O(32)(SeO(3))(4)(H(2)O)(2) (Ln = La, 1; Nd, 2) and Ln(2)Mo(3)O(10)(SeO(3))(2)(H(2)O) (Ln = Eu, 3; Dy, 4; Er, 5). Compounds 1 and 2 feature a complicated three-dimensional (3D) architecture constructed by the intergrowth of infinite molybdenum selenite chains of [Mo(4.75)SeO(19)](5.5-) and one-dimensional (1D) lanthanide selenite chains. The structures of 3, 4, and 5 exhibit 3D network composed of 1D [Mo(3)SeO(13)](4-) anionic chains connected by lanthanide selenite chains. The molybdenum selenite chain of [Mo(4.75)SeO(19)](5.5-) in 1 and 2 is composed of a pair of [Mo(3)SeO(13)](4-) chains as in 3, 4, and 5 interconnected by a [Mo(1.75)O(8)](5.5-) double-strand polymer via corner-sharing. The lanthanide selenite chains in both structures are similar in terms of coordination modes of selenite groups as well as the coordination environments of lanthanide(III) ions. Luminescent studies at both room temperature and 10 K indicate that compound 2 displays strong luminescence in the near-IR region and compound 3 exhibits red fluorescent emission bands with a luminescent lifetime of 0.57 ms. Magnetic properties of these compounds have been also investigated.     

DFT calculations of magnetic parameters for molybdenum complexes and hydroxymethyl intermediates trapped on silica surface

Density functional theory (DFT) calculations of EPR parameters and their structure sensitivity for selected surface paramagnetic species involved in oxidative dehydrogenation of methanol over silica grafted molybdenum catalyst were investigated. Two surface complexes, Mo(4c)/SiO2 and {O(-)-Mo(4c)}/SiO2, as well as *CH2OH radical trapped on the SiO2 matrix were taken as the examples. The spin-restricted zeroth order regular approximation (ZORA) implemented in the Amsterdam Density Functional suite was used to calculate the electronic g tensor for those species. The predicted values were in satisfactory agreement with experimental EPR results. Five different coordination modes of the *CH2OH radical on the silica surface were considered and the isotropic 13C, 17O, and 1H hyperfine coupling constants (HFCC) of the resultant surface complexes were calculated. Structure sensitivity of the HFCC values was discussed in terms of the angular deformations caused by hydrogen bonding with the silica surface.     

Mn(approximately)2.4Mo6O9: first example of empty twin chains of edge-sharing M6 octahedra in transition metal cluster chemistry

The novel ternary reduced molybdenum oxide Mn(approximately)(2.4)Mo(6)O(9) has been synthesized by solid-state reaction at 1400 degrees C for 96 h in sealed molybdenum crucibles. Electron diffraction studies showed that Mn(approximately)(2.4)Mo(6)O(9) presents a complex crystal structure with a 3d incommensurate modulation. The average crystal structure was determined on a single-crystal by X-ray diffraction in the orthorhombic space group Pnma with the following lattice parameters: a = 16.4824(2) A, b = 2.8273(2) A, c = 17.3283(2) A, Z = 4. The Mo network consists of empty twin chains of trans-edge-sharing octahedra that occur for the first time in a solid-state compound. The Mo-Mo distances within the chains 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. Single-crystal resistivity measurements show that Mn(approximately)(2.4)Mo(6)O(9) is metallic between 4.2 and 300 K. The magnetic susceptibility data indicate paramagnetic behavior due to the Mn(2+) moment at high temperatures with a weak ferromagnetic behavior below 80 K.     

Ligand-field photolysis of [Mo(CN)8]4- in aqueous hydrazine: trapped Mo(II) intermediate and catalytic disproportionation of hydrazine by cyano-ligated Mo(III,IV) complexes

The substitutional photolysis of K4[Mo(CN)8].2H2O in 98% N2H4.H2O has been investigated in detail. A molybdenum(II) intermediate, K5[Mo(CN)7].N2H4, is isolated in the primary stage of the reaction that involves the oxidation of N2H4 to N2, as evidenced by the analysis of evolving gases. The powder X-ray crystal structure of K5[Mo(CN)7].N2H4 indicates the pentagonal bipiramidal geometry of the anion and the presence of N2H4 in proximity to the CN(-) ligands. The salt is characterized by means of EDS, IR, UV-vis, and EPR spectroscopy as well as cyclic voltammetry measurements. The secondary stages of photolysis, involving the catalytic decomposition of N2H4 into NH3 and N2, lead to the formation of a molybdenum(IV) complex, [Mo(CN)4O(NH3)]2-. The monitoring of the amounts of evolving gases combined with UV-vis and EPR spectroscopic measurements at various stages of photolysis indicate that the molybdenum(III,IV) couple is catalytically active. The scheme of the catalytic decomposition of hydrazine is presented and discussed.     

Selective synthesis and characterization of single-crystal silver molybdate/tungstate nanowires by a hydrothermal process

Selective synthesis of uniform single crystalline silver molybdate/tungstate nanorods/nanowires in large scale can be easily realized by a facile hydrothermal recrystallization technique. The synthesis is strongly dependent on the pH conditions, temperature, and reaction time. The phase transformation was examined in details. Pure Ag(2)MoO(4) and Ag(6)Mo(10)O(33) can be easily obtained under neutral condition and pH 2, respectively, whereas other mixed phases of Mo(17)O(47), Ag(2)Mo(2)O(7,) Ag(6)Mo(10)O(33) were observed under different pH conditions. Ag(6)Mo(10)O(33) nanowires with uniform diameter 50-60 nm and length up to several hundred micrometers were synthesized in large scale for the first time at 140 degrees C. The melting point of Ag(6)Mo(10)O(33) nanowires were found to be about 238 degrees C. Similarly, Ag(2)WO(4), and Ag(2)W(2)O(7) nanorods/nanowires can be selectively synthesized by controlling pH value. The results demonstrated that this route could be a potential mild way to selectively synthesize various molybdate nanowires with various phases in large scale.     

Probing the self-assembly of inorganic cluster architectures in solution with cryospray mass spectrometry: growth of polyoxomolybdate clusters and polymers mediated by silver(I) ions

Cryospray mass spectrometry (CSI-MS) has been used to probe the mechanism of self-assembly of polyoxometalate clusters in solution. By using CSI-MS and electronic absorbance spectroscopy it was possible to monitor in real-time the self-assembly of polymeric chains based on [Ag 2Mo 8O 26] (2-) n building blocks. The role of the Ag (I) ion in the solution state rearrangement of molybdenum Lindqvist ({Mo 6}) into the silver-linked beta-octamolybdate ({Mo 8}) structure (( n-C 4H 9) 4N) 2 n [Ag 2Mo 8O 26] n ( 1) is revealed in unprecedented detail. A monoanionic series, in particular [AgMo m O 3 m+1 ] (-) where m = 2 to 4, and series involving mixed oxidation state polyoxomolybdate species, which illustrate the in-solution formation of the (Ag{Mo 8}Ag) building blocks, have been observed. CSI-MS detection of species with increasing metal nuclearity concomitant with increasing organic cation contribution supports the hypothesis that the organic cations used in the synthesis play an important structure-directing role in polyoxometalate (POM) growth in solution. A real-time decrease in [{Mo 6}] and associated increase in [{Mo 8}] have been observed using CSI-MS and electronic absorbance spectroscopy, and the rate of {Mo 6} interconversion to {Mo 8} was found to decrease on increasing the size of the countercation. This result can be attributed to the steric bulk of larger organic groups hindering {Mo 6} to {Mo 8} rearrangement and hindering the contact between silver cations and molybdenum anions.     

Structural, electrochemical and oxygen atom transfer properties of a molybdenum selenoether complex [Mo2O4(OC3H6SeC3H6O)2] and its thioether analogue [Mo2O4(OC3H6SC3H6O)2

The first crystallographically characterized molybdenum(vi) selenoether complex [Mo(2)O(4)(OC(3)H(6)SeC(3)H(6)O)(2)] and its thioether analogue [Mo(2)O(4)(OC(3)H(6)SC(3)H(6)O)(2)] were synthesised. Their structural, electrochemical and oxygen atom transfer properties are compared. This is relevant for the molybdenum cofactors of the DMSO reductase family where the coordination of the active site metal occurs through O (serine/aspartate), S (cysteine) or Se (selenocysteine). Both structures are almost identical except for those parameters that are directly derived from the different sizes of the varied ligand atoms (Se and S). No trans influence was observed. The metal centered redox process (Mo(V)<-->Mo(VI)) is at slightly lower voltage for the sulfur than for the selenium complex. The selenium compound catalyses the oxygen atom transfer from DMSO to PPh(3) by a different mechanism and at a higher rate than the sulfur compound, which is an indication that cysteine and selenocysteine might be used for a purpose in the different molybdenum and tungsten cofactors.     

Decamolybdocobaltate heteropolyanions in aqueous solutions: chemistry driving their formation and domains of stability

In the present study, aqueous solutions of decamolybdocobaltate H(4)Co(2)Mo(10)O(38)(6-) heteropolyanions were prepared from molybdenum oxide, cobalt carbonate precursors and hydrogen peroxide used as oxidizing agent. The preparation was optimized adding a consecutive hydrothermal treatment at 150 °C to obtain pure H(4)Co(2)Mo(10)O(38)(6-) aqueous solutions for Co/Mo atomic ratio of 0.5. Combining quantitative Raman and UV-visible measurements and chemometric methods, it was demonstrated that a mixture of H(4)Co(2)Mo(10)O(38)(6-) and octomolybdate Mo(8)O(26)(4-) species is obtained for Co/Mo ratios lower than 0.5, and the relative quantities of H(4)Co(2)Mo(10)O(38)(6-) are determined by the presence of Mo(8)O(26)(4-) species and by the quantity of Co(2+) countercations available in the solutions to ensure the electroneutrality. As these quantities can be predicted for each Co/Mo ratio, this finding allows rationalization of the preparation of heterogeneous catalysts using impregnation by H(4)Co(2)Mo(10)O(38)(6-) aqueous solutions. Parameters relevant of the impregnation step such as the pH, the Co/Mo ratio, and the molybdenum concentration were varied to determine the domains of stability of H(4)Co(2)Mo(10)O(38)(6-) heteropolyanions after formation. Stable from pH 1 to 4.5, this dimeric Anderson species is destabilized above pH 4.5; Co(2+), monomolybdate MoO(4)(2-) ions, and precipitates are then formed. For Co/Mo ratios lower than 0.5, the relative quantity of dimer does not vary with the pH and with a change of the Co/Mo ratio consecutive to the hydrothermal treatment. On the contrary, the coproduced Mo(8)O(26)(4-) species can be transformed into other isopolymolybdates varying the pH according to their domains of stability. For all of the ratios, H(4)Co(2)Mo(10)O(38)(6-) dimers were also shown to be stable in a wide range of molybdenum concentrations.     

The lengths of molybdenum to molybdenum quadruple bonds: correlations, explanations, and corrections

A systematic search of the Cambridge Crystallographic Database has yielded structures of 467 molecules containing, or reported to contain, a molybdenum to molybdenum quadruple bond, Mo[quadruple bond]Mo. We have arranged these data as a histogram, in order to determine the "normal" range of Mo[quadruple bond]Mo lengths, 2.06-2.17 A, as well as to examine molecules in which the Mo[quadruple bond]Mo length deviates from the norm. We discuss 24 molecules with exceptionally long Mo[quadruple bond]Mo lengths. Another molecule, Mo(2)(pyNC(O)CH(3))(4), was previously reported to have an unusually short Mo[quadruple bond]Mo bond. However, the structure is highly disordered (probably twinned); thus we have prepared and determined the structure of an analogous molecule, Mo(2)(pyNC(O)CH(2)CH(3))(4), which displays a completely normal Mo[quadruple bond]Mo bond length of over 2.08 A.     

Influence of Adding Molybdenum on Structure and Performance of FexOy/SBA-15 Catalysts in Selective Oxidation of Propene

Mixed iron and molybdenum oxide catalysts supported on nanostructured silica, SBA-15, were synthesized with various Mo/Fe atomic ratios ranging from 0.07/1.0 to 0.57/1.0. Structural characterization of as-prepared Mo_xO_y_Fe_xO_y/SBA-15 samples was performed by nitrogen physisorption, X-ray diffraction, and DR-UV-Vis spectroscopy. Adding molybdenum resulted in a pronounced dispersion effect on supported iron oxidic species. Increasing atomic ratio up to 0.21Mo/1.0Fe was accompanied by decreasing species sizes. Strong interactions between iron and molybdenum during the synthesis resulted in the formation of Fe−O−Mo structure units, possibly Fe₂(MoO₄)₃-like species. Reducibility of Mo_xO_y_Fe_xO_y/SBA-15 catalysts was investigated by temperature-programmed reduction experiments with hydrogen as reducing agent. The lower reducibility obtained when adding molybdenum was ascribed to both dispersion and electronic effect of molybdenum. Catalytic performance of Mo_xO_y_Fe_xO_y/SBA-15 samples was studied in selective gas-phase oxidation of propene with O₂ as oxidant. Adding molybdenum resulted in an increased acrolein selectivity and a decreased selectivity towards total oxidation products.     

Hydrothermal synthesis of the first vanadomolybdenum polyoxocation with a "metal-bonded" spherical framework

The heteropoly compound [(V(V)O(4))Mo(VI)(12)O(36)(V(IV)O)(6)][(OH)(9)].11H(2)O (1), synthesized by hydrothermal method under weak basic conditions, represents the first mixed Mo/V six-capped Keggin structural derivative with a spherical skeleton, and the first transition metal polyoxocation. The successful synthesis of 1 demonstrates that basic hydrothermal synthesis might be a power synthetic route to the isolation of more new polycationic metal-oxo clusters.     

氮、磷、碳化物比较研究初探

环保法规的日益严格使得研究者越来越重视新型加氢脱硫、脱氮催化剂的开发。国内外学者在对负载型Mo—Co、Mo—Ni和W—Ni等传统硫化物催化剂进行不断改进的同时，新型催化材料尤其是具有贵金属性质的过渡金属间充化合物一氮化物、碳化物和磷化物的研究也受到很大的关注。人们在探索不同的载体或者是不同的助剂对单金属间充化合物-氮化物、碳化物或磷化物催化剂活性组分的表面状态和结构以及其深度加氢脱硫脱氮性能的影响，而对同一载体负载的氮、磷、碳化物催化剂缺乏横向的比较。本研究制备了以γ-Al2O3为载体的负载型氮化钼、磷化钼和碳化钼催化剂，比较了它们的孔结构、比表面积，并初步分析了钼的质量分数为19％，氮化、磷化和碳化温度均为650℃时三类催化剂的二苯并噻吩加氢脱硫性能。     

Synthesis, properties, and crystal structure of a novel anthracene-bridged molybdenum-zinc porphyrin dimer

The synthesis and properties of novel anthracene-bridged porphyrin dimers having an oxomolybdenum(V) porphyrin unit, H(2)(DPA)[Mo(V)O(OMe)] (1) and (DPA)[Mo(V)O(OMe)][Zn(II)(MeOH)] (2), and the relevant monomer porphyrin complexes Mo(V)O(MPP)OMe (3) and Zn(II)(MPP) (4) are presented. An oxomolybdenum(V) unit was introduced into one of the two porphyrins in DPA to give 1, which has a free-base porphyrin unit. By introducing a zinc(II) ion to the free-base part, a mixed-metal complex of 2 was prepared and isolated. The structure of 2 was analyzed by X-ray crystallography (2.(7)/(6)CH(2)Cl(2), triclinic, P(-)1 (no. 2), a = 15.2854(12) A, b = 19.9640(15) A, c = 13.6915(12) A, alpha = 90.968(3), beta = 113.108(4), gamma = 96.501(4), Z = 2, R1 = 9.9, wR2 = 19.2). The structure of 2 demonstrated that a methanol is stably coordinated to the Zn(II) ion with the aid of a hydrogen bond to the methoxo ligand on the Mo(V) ion in the binding pocket of DPA. The electrochemical measurements of 2 suggested that the methanol was kept in the pocket of DPA in solution even at the reduced state of the molybdenum ion.     

Synthesis and characterization of ultrathin multilayer films based on molybdenum polyoxometalate (Mo(54))

The crown-shaped molybdenum polyoxometalate cluster Na(26)[[Na(H(2)O)(2)](6)[(micro(3) -OH)(4) (Mo(20)(V)), (Mo(34)(VI)(O)(164) (micro-CH(3)COO(4)) x 120H(2)O(Mo(54)) was synthesized and first used as a bulk modifier to fabricate a three-dimensional modified WIGE electrode by the layer-by-layer method. The (Mo(54))/PAH)(n) multilayer films have been characterized by X-ray photoelectron spectra (XPS) and atomic force microscopy (AFM). UV-vis measurements reveal regular film growth with each Mo(54) adsorption. The electrochemical method was used to characterize the modified WIGE electrode, which is important for practical applications.