Isothermal gravimetry and magnetic properties of CoOMoO3γAl2O3 catalysts

Isothermal gravimetry and magnetic susceptibility of MoO₃, MoAl₂O₃, CoAl₂O₃ and CoMoAl₂O₃ with/without Na⁺ ions have been studied in order to investigate the reducibility of the systems in H₂ H₂—hydrocarbons and H₂—hydro-carbon—thiophene. These studies have evidenced the formation of metallic cobalt during reduction of cobalt—moly catalysts containing Na⁺ ions in the Al₂O₃ support. This metallic cobalt accelerates the reduction of supported MoO₃. However, in the absence of sodium, cobalt exerts an inhibitory influence on the reduction of MoAl₂O₃. The inhibition is caused mainly due to retention of the water evolved during the process by well-dispersed Co²⁺ ions which are incapable of undergoing reduction. The presence of sulfur also kelps in suppressing the reduction to cobalt metal.     

Ternary chalcogenide compounds AB2X4: The crystal structures of SiPb2S4 and SiPb2Se4

The crystal structures of SiPb₂S₄ and SiPb₂Se₄ were determined from three dimensional X-ray diffraction data collected with Mo radiation. Both structures are monoclinic with space group $\text{P2}{}_1\text{c}$ and 4 formula units per unit cell. Lattice dimensions for SiPb₂S₄ are a = 6.4721(5) Å, b = 6.6344(9) Å, c = 16.832(1) Å, and β = 108.805(7)°. For SiPb₂Se₄, a = 8.5670(2) Å, b = 7.0745(3) Å, c = 13.6160(3) Å, and β = 108.355(3)°. The Si is tetrahedrally coordinated to S and Se with SiS about 2.10 Å and SiSe about 2.27 Å. The structural framework can be described as consisting of trigonal prisms of S or Se atoms which form a prismatic tube by sharing the triangular faces. These tubes in turn share edges to form corrugated sheets, with the unshared edges projecting alternately on each side of the sheet. The structures are very similar but not identical. In the sulfide one Pb is in sevenfold coordination and the other crystallographically independent Pb is in eightfold coordination. The PbS distances range from 2.82–3.50 Å. In SiPb₂Se₄ both Pb atoms are in sevenfold coordination. PbSe distances range from 2.97 to 3.54 Å. In the sulfide the Pb atoms form a zig-zag chain within the channels formed by the prismatic tubes while in the selenide they are in a straight line.     

Elucidation of hydrodesulfurization mechanism on molybdenum‐based catalysts using 35S radioisotope pulse tracer methods

Elucidation of the hydrodesulfurization (HDS) mechanism on molybdenum‐based catalysts using radioisotope tracer methods and reaction kinetics is reviewed. Firstly, to investigate the sulfidation state in Mo/Al₂O₃ and Co–Mo/Al₂O₃ catalysts, presulfiding of these catalysts has been performed using a ³⁵S pulse tracer method. Secondly, HDS of radioactive ³⁵S‐labeled dibenzothiophene was carried out over a series of sulfided molybdena–alumina catalysts and cobalt‐promoted molybdena–alumina catalysts in a pressurized flow reactor to estimate the behavior of sulfur on the working catalysts. Finally, sulfur exchange of a ³⁵S‐labeled catalyst with hydrogen sulfide was performed to estimate the relationship between the amount of labile sulfur and catalytically active sites.     

An infrared study of molybdenum /V/ hydroxide

The IR spectra of paramagnetic Mo/V/ oxygen compounds that are claimed in the literature to be unstable, were measurement in the 4000–3000 and 1200–250 cm^?1 regions. The spectra are poor but show a few bands in the valence and in the OH groups vibrations regions. Mo/V/ hydroxide can be reversibly or irreversibly dehydroxylated thermally in vacuum. The irreversible dehydroxylation of amorphous species containing Mo/V/ hydroxide takes place at >350°C, and is connected with a rearrengement of the atomic OMoO linkage and with crystallization of MoO₃, MoO₂ and Mo₄O₁₁ phases.     

Transition metal compounds containing the -OTeF5 and NTeF5 groups.

The electronegative ligand OTeF₅ has been tested on the elements Ti, Mo, W, Ta, Re, Os and others. Compounds such as OMo(OTeF₅)₄, W(OTeF₅)₆, Ta(OTeF₅)₅, ReO₂(OTeF₅)₃, OsO(OTeF₅)₄ are prepared. While ReVII could be stabilized with OTeF₅, the highest oxidation state on Osmium is VI, and Iridium probably IV. OMo(OTeF₅)₄ shows a regular square pyramidal structure with apical double bonded oxygen. Chemistry on the ligand NTeF₅ is based on the synthesis of H₂NTeF₅ and R₃SiNHTeF₅¹. Other new main group derivatives are so far Cl₂NTeF₅, HClNTeF₅, OCN-TeF₅, F₃PNTeF₅, Cl₃NPTeF₅, F₂SNTeF₅ and Cl₂SeNTeF₅, the first compound with a selenium-nitrogen double bond. In the transition metal series the compounds F₄MoNTeF₅ and Cl₄WNTeF₅ (in addition to the longer known polymeric (HgNTeF₅¹) have been prepared. Both have discrete metal nitrogen double bonds.     

The characteristic IR spectra of heterothiometallic cluster compounds

This article summarizes and presents the obtainable characteristic IR spectra of the existing heterothiometallic cluster compounds containing the [MXS₃]²⁻ (X=O, S; M=V, Mo, W, Re) moiety. The MS stretching vibration modes are classified into four categories including ν(MS_t), ν(Mμ₂-S), ν(Mμ₃-S) and ν(Mμ₄-S) according to the different conjunction ways between the transition metal and sulfur atoms. The structures of the heterothiometallic cluster compounds could be inferred from their characteristic IR spectra, the core structure's symmetry of the heterothiometallic clusters and the M/M′ ratio.     

The microwave spectrum of isoselenocyanic acid,HNCSe

A new molecular species has been detected by passing HBr gas through dry AgNCSe, which is shown by consideration of the rotational constants of the four isotopic species H¹⁴N¹²C⁸⁰Se, H¹⁴N¹²C⁷⁸Se, H¹⁴N¹³C⁸⁰Se and D¹⁴N¹²C⁸⁰Se to be HNCSe. The spectrum is consistent with that of a quasilinear molecule. A preliminary structure has been determined having r(HN) = 0.99 A, r(NC) = 1.95 A, r(CSe) = 1.717 A and a mean HNC angle of 143°. The quadrupole interaction parameter eQq = 1.17 MHz and the dipole moment component μ_a = 1.98 D have also been determined.     

Synthesis and reactivity of compounds of formula W(S)(OR)4

In ethereal solutions, WSCl₄ and 4 equiv LiOR (R = Bu^t or Prⁱ) react to form compounds of formula W(S)(OR)₄. A single-crystal X-ray diffraction study of W(S)(O-Bu^t)₄ showed it to have a square-based pyramidal geometry with an apical sulfide ligand. Pertinent bond distances (Å) and angles (°) are: WS = 2.1396(13), WO(av.) = 1.886(3), SWO(av.) = 105.09(10), WOC(av.) = 143.47(27). The tert-butoxide compound is stable toward sulfur atom abstraction by phosphines, and neither compound has shown any tendency to undergo comproportionations with W₂(OR)₆ (R = Prⁱ or CH₂Bu^t) species to form compounds of formula W₃(μ₃-S)(OR)₁₀, in direct contrast to analogous molybdenum and tungsten oxo alkoxides.     

Chevrel phases: An analysis of their metal-metal bonding and crystal chemistry

A useful measure of the total MoMo bonding in diverse phases containing Mo₆Y₈-type clusters (Y = S, Se, Cl, Br) is given by the Pauling bond order sum per electron ($\text{PBO}\text{e}$). These fall into two classes: (a) strongly bonded examples with $\text{PBO}\text{e}$ values near 1.00 which contain either discrete clusters with extra outer (exo) atoms or infinite confacial clusters, and (b) the rhombohedral Mo₆Ch₈ and M_xMo₆Ch₈ Chevrel phases with reduced $\text{PBO}\text{e}$ values of 0.72–0.84 in which face-capping chalcogenide (Ch) must also fill exo positions. The matrix effect in the latter which is responsible for the reduced bond orders arises from a combination of particularly strong MoCh intercluster bonds and closed-shell ChCh repulsions [3.31 å (S), 3.38 å (Se)], which force an elongation of the Mo₆ trigonal antiprism and reduce the MoMo bonding. There is no distinction between sulfide and selenide Chevrel phases in the degree of total MoMo bonding as expressed in bond orders. Changes in the structure on reduction are analyzed; the major effects come from loosening of the intercluster MoCh bonding and thence a decreased distortion (matrix effect) together with a flexing of the Mo₆Ch₈ host according to the size and charge of M. Distance considerations indicate substantial covalency between some M and Ch2, especially Pb and Ag, while cell volumes and MoCh₂ distances suggest significant constriction occurs in phases with higher charged M, possibly owing to compression by the host lattice and coulombic contributions to binding. Evidence for MoM bonding with M = Fe, Co, Ni is also noted. Intercluster interactions and MoMo bonding in Mo₆S₆Br₂ and in the mixed Mo₆Ch₈Mo_nCh_m (n = 9,12) cluster phases are quite consistent with those in the Chevrel phases, the total MoMo bonding per electron increasing with cluster condensation owing principally to reduce ChCh repulsions.     

IR spectroscopic studies on metal carbonyl compounds XXI. The successful application of the high-energy factored (“non-rigorous”) force field for the analysis of the IR spectra of six isotopic species of Co(CO)3NO

The high-energy factored model (“CottonKraihanzel type”, non-rigorous force field) is capable of reproducing within ± 0.8 cm^?1 all the CO and NO stretching frequencies of six different isotopic species of Co(CO)₃NO, if the model is modified by the introduction of “effective atomic masses” which take into account that, in line with Miller's approach, the quantities dealt with refer to the composite properties of the MCO (or MNO) units. The results obtained by the same method for the isotopically substituted species of Ni(CO)₄, Fe(CO)₅, and M(CO)₆ [M  Cr, Mo, or W] are also in good agreement with experiment.     

Radiation stability of methionine-35S and selenomethionine-75Se

The radiation stability of methionine-³⁵S and selenomethionine⁷⁵Se was investigated using the methods of thin-layer chromatography, gas chromatography and ESR. Radiation decomposition of methionine-³⁵S mainly consists in an oxidation process and in the release of volatile products. The ESR-spectra of irradiated DL-methionine indicated a strong localization of the unpaired electrons on sulfur atoms. Radiation damage to selenomethionine-⁷⁵Se as a function of radiation dose proved an increased stability of this compound, and its radiation decomposition consists in the formation of oxidized products and by direct rupture of the selenium bonds accompanied by the formation of volatile compounds like CH₃SeH and SeH₂. The self-radiolysis of the aqueous solution of selenomethionine-⁷⁵Se during its storage in air leads, however, to a lower decomposition rate which consists in the release of inorganic selenium and in an oxidation process.     

Monoxidised Sulfur and Selenium Derivatives of 1,8‐Bis(diphenylphosphino)naphthalene: Synthesis and Coordination Chemistry

Treatment of 1,8‐bis(diphenylphosphino)naphthalene (dppn, 1 ) with stoichiometric amounts of sulfur or selenium in toluene at 80 °C selectively afforded the diphosphine monochalcogenides 1‐Ph₂P(C₁₀H₆)‐8‐P(:S)Ph₂ (dppnS, 2 a ) and 1‐Ph₂P(C₁₀H₆)‐8‐P(:Se)Ph₂ (dppnSe, 2 b ). The ³¹P{¹H} NMR spectrum of 2 b showed an unusually large ⁵J(P–Se) value, which indicates a significant through‐space coupling component. The monosulfide acted as a bidentate P,S‐ligand towards platinum(II) ( 3 a ), whereas the corresponding monoselenide complex ( 3 b ′) lost elemental selenium with formation of the previously reported complex [PtCl₂(dppn)‐P,P′] ( 3 ). Treatment of dppnSe with [(nor)Mo(CO)₄] (nor = norbornadiene) led to formation of [(dppnSe)Mo(CO)₄‐P,Se] ( 3 b ). Solutions of the latter slowly deposited Se with formation of [(dppn)Mo(CO)₄‐P,P′] ( 4 ) which was also obtained by independent synthesis from 1 and [(nor)Mo(CO)₄]. All isolated new compounds were characterised by a combination of ³¹P, ¹H, ¹³C and ⁷⁷Se ( 2 b ) NMR spectroscopy, IR spectroscopy, mass spectrometry and elemental analysis. Single‐crystal X‐ray structure determinations were performed for dppnSe ( 2 b ), [PtCl₂(dppnS)‐P,S] ( 3 a ), [(dppnSe)Mo(CO)₄‐P,Se] ( 3 b ) and [(dppn)Mo(CO)₄‐P,P′] ( 4 ). In 2 b steric effects cause the naphthalene ring to be distorted and force the phosphorus atoms by 65 and 59 pm to opposite sides of the best naphthalene plane. In the metal complexes 3 a , 3 b and 4 the phosphino‐phosphinochalcogenyl systems act as bidentate ligands through the P and the chalcogen atoms. The naphthalene systems are again distorted. The two independent molecules of 4 differ in their conformations.     

Lineare oligophosphaalkane: XVIII. Addition Ph-funktioneller methylenbisphosphane an die MoMo-Dreifachbindun in (η5-C5H5)2Mo2(CO)4

By means of the addition of the PH-functional methylenebisphosphanes R¹R²-PCH₂PR³H (PCP) to the MoMo triple bond in (η⁵-C₅H₅)₂Mo₂(CO)₄(MoMo) the complexes (η⁵-C₅H₅)₂Mo₂(CO)₄(PCP) containing a five-membered ring system Mo₂P₂C are obtained. Starting with unsymmetrically substituted methylenebisphosphanes R′₂PCH₂PRH only one isomer is formed, while the disecondary derivatives RHPCH₂PHR (as the diastereomeric mixture) gave two isomers of (η⁵-C₅H₅)₂Mo₂(CO)₄(PCP) (A₂ and AB) as indicated by the ³¹P{¹H} and ¹³C{¹H} NMR spectra.X-ray structural analysis of the derivative of the racemate of t-BuHPCH₂PH(t-Bu) space group C2/c, monoclinic, a 18.034(2), b 14.909(1), c 11.106(1) Å, α 90, β 99.788(8), γ 90°) reveals a puckered Mo₂P₂C five-membered ring system (dihedral angle PMoMo′P′ 54.4(2)°) with square-pyramidal coordination geometry at the Mo atoms. Two of the CO ligands (C(6)O(1) and C(6′)O(1′)) are almost coplanar with the molybdenum atoms, while the terminal CO groups (C(7)O(2) and C(7′)O(2′)) are about orthogonal (dihedral angle C(7)MoMo′C(7′) 88.4(3), MoMo′ 3.2109(4), MoP 2.4567(8), PC(8) 1.834(3), PH(P) 1.37(3) Å).     

Zweikernige η5-pentamethylcyclopentadienyl-rhenium-komplexe mit einer chalkogenbrücke. Die molekülstruktur von [(η5-C5Me5)Re(CO)2]2(μ-Se)

We report the synthesis and characterisation of binuclear η⁵-pentamethylcyclopentadienylrhenium complexes, [(η⁵-C₅Me₅)Re(CO)₂]₂(μ-E) (E = S (2), Se (3), Te (4)), containing a chalcogen bridge in addition to a ReRe bond. According to the X-ray structural analysis, 3 possesses approximately C₂ molecular symmetry; the C₅Me₅ ring ligands occupy trans positions with respect to the central Re₂Se unit [d(ReRe) 3.032(1) Å, ∢ ReSeRe 74.9(1)°]. As expected, the complexes of the now complete series [CpRe(CO)₂]₂(μ-E) (E = O (1), S (2), Se (3), Te (4)) show a high degree of similarity in their corresponding mass, IR, ¹H and ¹³C NMR spectra.     

The Reactions of Sulfur,Selenium and Tellurium with Fluorosulfuric Acid

Abstract

In fluorosulfuric acid, four different sulfur species: S₂ ⁺., S⁺., S(II+), S(IV+), 3 different selenium species: Se₂ ⁺., Se(II+), Se(IV+), and 3 different Tellurium species: Te₂ ²⁺, Te(II+) and Te(IV+) have been observed spectrophotometrically and electrochemically by varying the composition of the solvent from basic (non-oxidizing) medium (0.1M solution of NaSO₃F) to oxidizing media (0.5M solution of SO₃).     

Cationic complexes of trimethylplatinum(IV) with tridentate ligands—I. Preparation and characterization of complexes from a range of thio,seleno, thio-seleno,amino-thio and amino-seleno ligands

The new ionic complexes [PtMe₃{MeE(CH₂)_nE′(CH₂)_nEMe}]⁺X⁻ [n = 3; E = E′ = S : n = 2; E = Se or S; E′ = O, S, Se or SS: X = I, BPh₄ or BF₄] and [PtMe₃(H₂NCH₂CH₂)₂E′]+BF⁻₄ [E′ = O or SS] have been prepared and characterized by molar-conductivity measurements and ¹H NMR spectroscopy. The hitherto unreported ligands [(MeE(CH₂)_n)₂E′] (n = 3; E = E′ = S: n = 2; E = Se; E′ = O or S or Se: n = 2; E = S; E′ = Se] have been characterized by ¹H NMR and ⁷⁷Se NMR (where appropriate), and by mass spectroscopy.     

Synthese,structure cristalline et analyse vibrationnelle de l'hexathiohypodiphosphate de lithium Li4P2S6

The crystalline compound Li₄P₂S₆ is obtained either by devitrification of Li₄P₂S₇ glass at 450°C with sulfur formation or by crystallisation at 450°C of a Li₂S, P and S melt. The structure determination has been solved by X-ray diffraction on a monocrystal. The unit cell is hexagonal $\text{P6}{}_3\text{mcm}$ with a = 6.070(4), c = 6.577(4) Å, V = 209 ų, Z = 1. Intensities were collected at 293°K with Kα (λ = 0.71069 Å) Mo radiation on an automatic Nonius CAD-4 diffractometer. The structure was solved under the assumption of random disorder of P atoms over two sites (occupancy factor of 0.5). Anisotropic least-squares refinement with W = 1 gave R = 0.047 for 90 independent reflections and 9 variables. The structure is built according to an ABAB sequence sulfur packing. Per unit cell, four out of six octahedral sites are occupied by Li ions, and the other two are statistically filled (0.5) by PP pairs. The PP central bond (2.256(13) Å) links two staggered PS₃ groups (PS = 2.032(5) Å) to form the D_3d symmetry P₂S^4?₆ anion. Infrared and Raman spectra show features very similar to those of Na₄P₂S₆, 6H₂O and M^IIPS₃ compounds. A new assignment in terms of symmetry species is proposed for the P₂S₆ internal modes, which is confirmed by a normal coordinate calculation using a valence force field; the stretching force constants f_PP and f_PS are equal to 1.6 and 2.7 mdyne Å^?1, respectively.     

95Mo NMR spectral studies on seven-coordinate molybdenum(II) isocyanide complexes

The ⁹⁵Mo NMR spectra of a series of seven-coordinate molybdenum(II) isocyanide complexes of the types [Mo(CNR)_7-nL_n](PF₆)₂ (R = CH₃, CHMe₂, CMe₃, C₆H₁₁, CH₂Ph; L = py, bpy, Me₂bpy, phen, dppe, P-n-Bu₃; n = 0,1,2) [Mo(CNC-Me₃)₆X]PF₆ (X = Cl, Br, I) and [{Mo(CNCMe₃)₄(NN)}₂(μ-CN)](PF₆)₃ (NN = bpy, Me₂bpy, phen) have been studied. The ⁹⁵Mo chemical shift range for this group of complexes is about 1100 ppm. An increase in the size of the R group attached to the isocyanide ligand generally tends to shield the ⁹⁵Mo nucleus. Replacement of the isocyanide ligand with a phosphorus ligand also increases the shielding, whereas the replacement of isocyanide with a heterocyclic nitrogen donor leads to deshielding by 800–900 ppm. This group of complexes shows a normal halogen dependence, i.e. replacement of Cl^? by Br^? and I^? increases the shielding of the ⁹⁵Mo nucleus. The cyano-bridged cations [{Mo(CNCMe₃)₄(NN)}₂(μ-CN)]³⁺ (NN = bpy, Me₂bpy, or phen) show two ⁹⁵Mo NMR signals, one for the molybdenum coordinated to the carbon of the bridging CN and one for the N-coordinated molybdenum. Comparison of the chemical shifts and linewidths of the cyano-bridged species with those of the corresponding mononuclear molybdenum(II) complexes [Mo(CNCMe₃)₅(NN)](PF₆)₂ leads to the assignment of the more deshielded signal to the N-coordinated molybdenum. The ¹⁴N and ³¹P NMR spectra for these complexes have also been measured, as have the ¹³C NMR spectra of the pairs of complexes [Mo(CNCMe₃)₅(NN)](PF₆)₂ and [{Mo(CNCMe₃)₄(NN)}₂(μ-CN)](PF₆)₃ (NN = bpy or phen). The ¹⁸³W NMR spectra for [W(CNR)₅(bpy)](PF₆)₂ (R = CMe₃ and CH₂Ph), show that the δ(¹⁸³W)/δ(⁹⁵Mo) chemical shift ratios for isocyanide complexes are different from the ratio found for M⁰ and M^VI.     

Telluride clusters of molybdenum: Synthesis, structures, and NMR spectra

High-temperature reactions of Mo, chalcogen (S or Se), Te, and Br₂ in molar ratio Mo: S/Se: Te: Br = 3: 1: 6: 4 were carried out. The reaction products were subjected to mechanochemical activation with K(Dtp) (Dtp = (EtO)₂PS₂) in a vibrational mill, resulting in the formation of new compounds [Mo₃(μ₃-Q)_0.5(μ₃-O)_0.5(μ₂-Te₂)₃(Dtp)₃](Dtp) (Q = Se (I) and S (II)). The structure of compound I has been established by X-ray diffraction analysis. Solutions of compounds I and II contain mixtures of [Mo₃(μ₃-Q)(μ₂-Te₂)₃(Dtp)₃]⁺ and [Mo₃(μ₃-O)(μ₂-Te₂)₃(Dtp)₃]⁺, which is confirmed by mass spectrometry and ³¹P, ⁷⁷Se, and ¹²⁵Te NMR spectroscopy. Quantum-chemical calculations of the ¹²⁵Te NMR chemical shifts were performed. The compounds are also characterized by IR spectroscopy, Raman spectroscopy, and elemental analysis. Structure I contains short nonvalent contacts between the sulfur atom of the out-of-sphere Dtp anion and the axial tellurium atoms of the cluster.     

Phase equilibria for the system Mn0.394Ti0.606OS at 1380 and 1485°K

This paper reports equilibrium phase data for the manganese-containing system Mn_0.394Ti_0.606OS. The system was studied at 1380 and 1485°K by an equilibration and quench technique. The oxygen and sulfur fugacities of the equilibrating gas atmosphere were independently controlled using mixtures of the three gases hydrogen, carbon dioxide, and hydrogen sulfide. The results are presented on log f_S2 vs log f_O2 phase diagrams which are discussed in terms of the equilibria between manganese in the oxide phases and manganese in the α-MnS sulfide phase. The results are shown to be consistent with previously published data for the subsystems MnTiO, MnOS, MnS, and TiOS.