Structure and Reactivity of Gas‐Phase Molybdenum Oxide Cluster Ions

Combining the ion cyclotron resonance method and a Knudsen effusion source, we obtained a series of Mo_xO_y ⁺ (x = 1 – 5, y = 1 – 15) molybdenum oxide cluster ions. We studied the dependence of the concentrations of these ions on the trapping time and their reactions with carbon monoxide. It is shown that Mo_xO_y ⁺ ions with x > 3 contain a cyclic Mo₃O₉ fragment in their structure. The oxygen bond energies in Mo_xO_y ⁺ ionic clusters are estimated.     

Formation of mixed Fe-Mo oxo clusters in the gas phase

Reactions of oxygen-containing molybdenum clusters Mo_xO_y (x = 1–3, y = 1–9) with iron carbonyl ions Fe(CO) _n ⁺ (n = 1–3) were studied by the ion cyclotron resonance technique. The reactions were found to yield mixed Fe-Mo oxo clusters Mo_xO_yFe⁺ (x = 2, 3; y = 5, 6, 8, 9).     

Reactions of Neutral and Charged Molybdenum Oxide Clusters with Low-Molecular-Weight Alcohols in a Gas Phase Studied by Ion Cyclotron Resonance

A set of oxygen-containing molybdenum oxide clusters Mo _x O _y (x = 1–3; y = 1–9) was obtained with the use of a combination of a Knudsen cell and an ion trap cell. The reactions of positively charged clusters with C₁–C₄ alcohols were studied using ion cyclotron resonance. The formation of a number of organometallic ions, the products of initial insertion of molybdenum oxide ions into the C–O and C–H bonds of alcohols, and polycondensation products of methanol and ethanol were found. The reactions of neutral molybdenum oxide clusters Mo _x O _y (x = 1–3; y = 1–9) with protonated C₁–C₄ alcohols and an ammonium ion were studied. The following limits of proton affinity (PA) were found for neutral oxygen-containing molybdenum clusters: (MoO) < 180, (Mo₂O₄, Mo₂O₅, and Mo₃O₈) = 188 ± 8, PA(MoO₂) = 202 ± 5, PA(MoO₃, Mo₂O₆, and Mo₃O₉) > 207 kcal/mol.     

First Mixed Alkaline Uranyl Molybdates: Synthesis and Crystal Structures of CsNa3[(UO2)4O4(Mo2O8)] and Cs2Na8[(UO2)8O8(Mo5O20)]

Two new mixed alkaline uranyl molybdates CsNa₃[(UO₂)₄O₄Mo₂O₈] ( 1 ) and Cs₂Na₈[(UO₂)₈O₈(Mo₅O₂₀)] ( 2 ) have been obtained by high‐temperature solid state reactions. Their crystal structures have been solved by direct methods: Compound 1 : triclinic, P , a = 6.46(1), b = 6.90(1), c = 11.381(2) Å, α = 84.3(1), β = 91.91(1), γ = 80.23(1)°, V = 488.6(2) ų, R₁ = 0.06 for 2865 unique reflections with |F_o| ≥ 4σ_F; Compound 2 : orthorhombic, Ibam, a = 6.8460(2), b = 23.3855(7), c = 12.3373(3) Å, V = 1975.2(1) ų, R₁ = 0.049 for 2120 unique reflections with |F_o| ≥ 4σ_F. The structure of 1 contains complex sheets of UrO₅ pentagonal bipyramids and molybdenum polyhedra. The sheets have [(UO₂)₂O₂(MoO₅)] composition. Natrium and cesium atoms are located in the interlayer space. Cesium atoms are situated between the molybdenum clusters, whereas natrium atoms are segregated between the uranyl complexes. The large Cs⁺ ions are localized between the Mo₂O₉ groups and force the molybdenum polyhedra to rotate relative to the [(UO₂)₂O₂(MoO₅)] sheets. Such rotation is impossible for U⁶⁺ polyhedra due to their rigid edge‐sharing complexes. The distance between the U⁶⁺ polyhedra vertices of neighboring layers is 3.8 Å, that allows the Na⁺ ion to be positioned between the uranyl groups. The crystal structure of 2 is based upon a framework consisting of [(UO₂)₂O₂(MoO₅)] sheets parallel to (010). The sheets are linked into a 3‐D framework by sharing vertices with the Mo(2)O₄ tetrahedra, located between the sheets. Each MoO₄ tetrahedron shares two of its corners with two MoO₆ octahedra in the sheet above, and the other two with MoO₆ octahedra of the sheet below. Thus four MoO₆ octahedra and one MoO₄ tetrahedron form chains of composition Mo₅O₁₈. The resulting framework has a system of channels occupied by the Cs⁺ and Na⁺ ions.     

MALDI-TOF Mass Spectrometry of Nanosized MoO<Subscript>2</Subscript>. Structure and Relative Stability of Isomers of Lower Molybdenum Oxide Cations

MALDI-TOF was used to study molybdenum dioxide (MoO₂) containing a nanosized fraction. The composition of cationic clusters of nonstoichiometric lower molybdenum oxides in the gas phase was determined, and the thermodynamic stabilities and configurations of isomers were calculated for selected symmetric molecular structures and for cations MoSO ₈ ⁺ and Mo₅O ₉ ⁺ . Molecular orbital analysis was performed for two trigonal-bipyramidal clusters Mo₅O₈ and Mo₅O₉. Changes in molybdenum–molybdenum interatomic distances in going from MoO ₈ ⁺ and Mo₅O ₉ ⁺ cations to neutral clusters are discussed.     

Control over the self-assembly of polymers and layered molybdenum oxide: from the micrometer scale to the molecular scale

We report adjustment on the self-assembly between polymer of polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA) and inorganic molybdenum oxide layers from the micrometer scale to the nanometer scale. Our method is to break the strong interactions between the organic polymers by introducing suitable bridging agents and adjust the reaction speeds of the two competitive reactions in the reaction system. We use I₂ to complex with PVA and break the strong hydrogen interactions between the PVA chains, resulting in a PVA-I₂/(Mo_xO_y)_∞ⁿ⁻ complex, in which the organic and inorganic species self-assemble homogenously on the molecular scale. We also adjust the thickness of the inorganic (Mo_xO_y)_∞ⁿ⁻ layers in the hybrid of PVP/(Mo_xO_y)_∞ⁿ⁻ by controlling the reaction speeds of the two competitive reactions: hydrolysis of Mo₇O₂₄ ⁶⁻ into (Mo_xO_y)_∞ⁿ⁻ and packing into thick inorganic layers on the one hand, and hybridization of (Mo_xO_y)_∞ⁿ⁻ and PVP into layered hybrid on the other hand. Experimental results proved that when the hydrolysis is overwhelming, the inorganic molybdenum oxide chains pack into heavy layers and self-assemble with PVP polymers on the micrometer scale, and when the hybrid reaction dominates, the organic polymer and molybdenum oxide hybridize on the molecular scale. These findings open new routes to disperse organic polymer and inorganic species homogenously and fabricate novel organic/inorganic hybrid nanomaterials in situ.     

Heat capacities and densities of mixtures of very polar substances. 3. Mixtures containing either trichloromethane or 1,4-dioxane or diisopropylether

Excess molar heat capacities C _P ^E at constant pressure and excess molar volumes V ^E have been determined, as a function of mole fraction x₁ at 25°C and atmospheric pressure, for 10 binary liquid mixtures containing either trichloromethane (series I) with C₆H₅CH₃, or C₆H₅Cl, or C₅H₅N, or CH₃COCH₃, or C₆H₅NO₂; 1,4-dioxane (series II) with (C₂H₅)₃N, or (CH₃)₂CHOCH(CH₃)₂, or (CH_{3 2}SO); or diisopropyl ether (di-1-methylethyl ether) (series III) with (C₂H₅)₃N, or CHCl₃. The dipole momentsp (10^–30C-m) of the substances range from nearly 0 to 14.1 for nitrobenzene. The C _P ^E of series I and III are all positive, with C _P ^E (x₁=0.5) (J-K^–1-mol^–1) ranging from 1.04 for {x₁CHCl₃+x₂C₆H₅Cl} to 16.66 for {x₁(CH₃)₂CHOCH(CH₃)₂+x₂CHCl₃}. In series II, the C _P ^E are positive and small for {x₁1,4-C₄H₈O₂+x₂(CH₃)₂CHOCH(CH₃)₂}, S-shaped and small for {x₁1,4-C₄H₈O₂+x₂(C₂H₅)₃N}, and negative and small for {x₁1,4-C₄H₈O₂+x₂(CH₃)₂SO}. The excess volumes are small and positive for {x₁CHCl₃+x₂C₆H₅CH₃}, S-shaped for {x₁CHCl₃+x₂CH₃COCH₃}, {x₁1,4-C₄H₈O₂+x₂(C₂H₅)₃N} and {x₁(CH₃)₂CHOCH(CH₃)₂+x₂(C₂H₅)₃N}, and negative for the other systems.Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday     

Neutral counterparts of the C2H7O+ isomers

The neutral counterparts of the C₂H₇O⁺ isomers CH₃O⁺ (H)CH₃, CH₃CH₂OH₂⁺ and $ {\rm C}_2 \,{\rm H}_4 \,\, \cdot \cdot \cdot \mathop {\rm H}\limits^ + \, \cdot \cdot \cdot {\rm OH}_2 $ were studied by neutralization-reionization mass spectrometry. Protonated dimethyl ether and its —O(D)⁺ analogue were produced by protonation (deuteration) of dimethyl ether and also generated as a fragment ion from (labeled) ionized CH₃OCH₂CH(OH)CH₃ by loss of CH₃CO?. It was observed that the dissociation characteristics of the ions and the stability of their neutral counterpart depended on the internal energy of the protonated ether ions. Stable neutral CH₃?(H)CH₃ was only produced from energy-rich ions. The classical protonated ethanol ion CH₃CH₂OH₂⁺ (a) was produced at threshold by the loss of CH₃CO?. from ionized butane-2,3-diol. Mixtures of a with the non-classical ion $ {\rm C}_2 \,{\rm H}_4 \,\, \cdot \cdot \cdot \mathop {\rm H}\limits^ + \, \cdot \cdot \cdot {\rm OH}_2 $ (b) were produced by reaction of C₂H₅⁺ ions with H₂O. As for the protonated ether, only high-energy a and/or b ions yielded stable hypervalent radicals. It is suggested that the stable C₂H₇?O radicals are Rydberg states.     

Possibility of Mo<Subscript>2</Subscript>O<Subscript>6</Subscript> formation at high temperatures in the range of pressures from 1 to 1 × 10<Superscript>−5</Superscript> bar

Gibbs free energy minimization was used to consider the formation of complex molybdenum oxide (Mo₂O₆) at 2400 K in the range of pressures from 1 to 1 to 1 × 10⁻⁵ bar for the basic component ratio Mo: O₂ = 1: 1. Several ways are shown to lead to Mo₂O₆ formation: when P = 1 bar, a synthesis reaction involving simple molybdenum oxides (MoO, MoO₂, MoO₃) is the main way; when P = 1 × 10⁻³ bar or lower, reactions of (MoO₃) _n (n = 3−5) complex oxides with metallic molybdenum and molybdenum monoxide (MoO) are.     

Photofragmentation of 2‐Deoxy‐D‐Ribose Molecules in the Gas Phase

We have measured the synchrotron‐induced photofragmentation of isolated 2‐deoxy‐D ‐ribose molecules (C₅H₁₀O₄) at four photon energies, namely, 23.0, 15.7, 14.6, and 13.8 eV. At all photon energies above the molecule′s ionization threshold we observe the formation of a large variety of molecular cation fragments, including CH₃⁺, OH⁺, H₃O⁺, C₂H₃⁺, C₂H₄⁺, CH_xO⁺ (x=1,2,3), C₂H_xO⁺ (x=1–5), C₃H_xO⁺ (x=3–5), C₂H₄O₂⁺, C₃H_xO₂⁺ (x=1,2,4–6), C₄H₅O₂⁺, C₄H_xO₃⁺ (x=6,7), C₅H₇O₃⁺, and C₅H₈O₃⁺. The formation of these fragments shows a strong propensity of the DNA sugar to dissociate upon absorption of vacuum ultraviolet photons. The yields of particular fragments at various excitation photon energies in the range between 10 and 28 eV are also measured and their appearance thresholds determined. At all photon energies, the most intense relative yield is recorded for the m/q=57 fragment (C₃H₅O⁺), whereas a general intensity decrease is observed for all other fragments— relative to the m/q=57 fragment—with decreasing excitation energy. Thus, bond cleavage depends on the photon energy deposited in the molecule. All fragments up to m/q=75 are observed at all photon energies above their respective threshold values. Most notably, several fragmentation products, for example, CH₃⁺, H₃O⁺, C₂H₄⁺, CH₃O⁺, and C₂H₅O⁺, involve significant bond rearrangements and nuclear motion during the dissociation time. Multibond fragmentation of the sugar moiety in the sugar–phosphate backbone of DNA results in complex strand lesions and, most likely, in subsequent reactions of the neutral or charged fragments with the surrounding DNA molecules.     

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.     

The electrochemical properties of a platinum electrode in functionalized room temperature imidazolium ionic liquids

The electrochemical behavior of a platinum electrode in a set of 1-alkyl ether (and 1-alkyl)-3-methylimidazolium room-temperature ionic liquids (RTILs) 1–3 ([C_xO_yMim]⁺[Anion]⁻ or [C_xMim]⁺[Anion]⁻, where Mim = 3-methylimidazolium; C_xO_y = 1-alkyl ether; C₇O₃ = -(CH₂)₂O(CH₂)₂O(CH₂)₂OCH₃; C₃O₁ = -(CH₂)₂OCH₃; C_x = 1-alkyl; C₁₀ = C₁₀H₂₁; C₄ = C₄H₉; and ) was studied by cyclic voltammetry and electrical conductivity. This complementary set of imidazolium RTILs allowed us to explore the effect of the imidazolium cation and the counter-ion, both of which affected the electrochemical window of these RTILs. Various electrochemical events with low current values were observed, which diminished the electrochemical windows. Interestingly, RTILs 2b [1-(2-methoxyethyl)-3-methylimidazolium tetrafluoroborate] and 2d [1-butyl-3-methylimidazolium tetrafluoroborate] showed quasireversible charge transfer processes. The length of the functional group attached to the imidazolium cation was shown to be of great influence as larger electrochemical windows, as well as lower electrical conductivities, were obtained with the longer C₇O₃ and C₁₀ functional groups. The largest electrochemical window of 2.0 V was achieved with RTIL 2c, 1-decyl-3-methylimidazolium tetrafluoroborate. Dedicated to the memory of Prof. Francisco Nart.     

Synthesis and Crystal Structure of Two New Molydenum(V) Pyrophosphate Complexes

Two new reduced molybdenum pyrophosphates, Na₂₈[Na₂{(Mo₂O₄)₁₀(P₂O₇)₁₀(HCOO)₁₀}]·108H₂O ( 1 ) and Na₂₂(H₃O)₂[Na₄{(Mo₂O₄)₁₀(P₂O₇)₁₀(CH₃COO)₈(H₂O)₄}]·91H₂O ( 2 ) have been synthesized and characterized by single‐crystal X‐ray diffraction. Red crystals of 1 are triclinic, space group , with a = 17.946(4) Å, b = 18.118(4) Å, c = 21.579(4) Å, α = 114.47(3)°, β = 93.54(3)°, γ = 114.39(3)° and V = 5581.8(19) ų, and orange crystals of 2 are monoclinic, space group P2₁/n, with a = 21.467(4) Å, b = 23.146(5) Å, c = 24.069(5) Å, β = 101.76(3)° and V = 11708(4) ų. They are both constructed by Mo^V dimers ({Mo₂O₄(O_P)₄(HCOO)} in 1 , {Mo₂O₄(O_P)₄(CH₃COO)} and {Mo₂O₄(O_P)₄(H₂O)₂} in 2 ) and pyrophosphoric groups. Their structures can be described as two interconnected nonequivalent wheels which are approximately perpendicular, delimiting a large cavity. The larger wheel contains six Mo^V dimers, while the smaller one has four dimers.     

Relative stability of isomers of polynuclear complexes of molybdenum oxides

Molybdenum(VI) oxide MoO₃ has been studied and the composition of polynuclear molybdenum oxides in the gas phase Mo _x O_{3x ? y} (x = 1–6, y = 0–2) has been determined by laser desorption/ionization time-of-flight mass spectrometry. Quantum-chemical calculations of bond energies, interatomic distances, charge distributions, and molybdenum-molybdenum bond orders for the isomers of neutral polynuclear molecular compounds Mo _x O3 _{x ? y} have been performed with the use of the PBE functional with a relativistically corrected potential implemented as the PRIRODA program package. On the basis of the bond energies, the relative stability of the isomers has been estimated. For the Mo _x O _y isomers (x ≥ 3), cyclic structures have been predicted to be more favorable. For the predicted most stable isomers of each Mo _x O _y composition, the bond energies of their positive and negative ions have been calculated. The positive ionization of Mo _x O _y leads to a considerable decrease in the bond energy of the isomer and the negative ionization, to its increase by about 0.1 au.     

Heterometallic Alkoxides of Molybdenum and Heavy Transition Metals—the Synthesis and Prospects of Application

The alkoxides of molybdenum and other heavy transition elements such as Ta or Nb were found to be unreactive towards each other. The bimetallic derivatives could be obtained either via partial hydrolysis that gave Mo₂Ta₄O₈(OMe)₁₆ (I) or via partial thermolysis that provided access to Mo₄Ta₂O₈(OⁱPr)₁₄ (II), Mo₃Ta₂O₈(OⁱPr)₁₀ (III), Mo₄Ta₄O₁₆(OⁱPr)₁₂ (IV), Mo₄Nb₂O₈(OⁱPr)₁₄ (V) and Mo₄W_2–x Mo _x O₁₀(OⁱPr)₁₂ (VI). I–VI can be isolated only from hydrocarbon media as the presence of alcohols leads to precipitation of insoluble homometallic derivatives of molybdenum. The cathodic reduction of MoO(OR)₄ (R = Me, Et) in the presence of LiCl and M(OR)₅ (M = Nb, Ta) leads only to formation of LiMo₂O₂(OMe)₇(MeOH) (VII) or LiMo₂O₂(OEt)₇ (VIII) respectively.     

The reactions of polyacetylene with trimethyloxonium hexachloroantimonate. Covalent doping of (CH)x

Polyacetylene, (CH)_x, has been doped with trimethyloxonium hexachloroantimonate, (CH₃)₃O⁺SbCl(1), in dichloromethane and acetonitrile. The maximally doped (CH)_x films have moderate conductivities [σ_RT(CH₂Cl₂) = 10, σ_RT(CH₃CN) = 0.7 Ω^?1 cm^?1]. Reactions between 1 and (CH)_x CH₂Cl₂ or CH₃CN were followed in situ by ¹H nuclear magnetic resonance spectroscopy and x-band electron spin resonance spectroscopy. It was found that the reactions in the two solvents are different. In dichloromethane the dopant is SbCl₅, which forms from the decomposition of 1, and doping proceeds by electron removal from (CH)_x chains. Based on the ESR signal loss, an estimate can be made of the diffusion rate of SbCl₅, into the (CH)_x fibrils in CH₂Cl₂; it is found to be ca. 10^?17 cm²/s. In acetonitrile the dopant appears to be either CH₃CNCH, H⁺, CH, or a combination of one or more of these dopants. It is postulated that the CH₃CNCH, CH, and/or H⁺ dopant covalently binds to the (CH)_x chain. X-ray photoelectron spectra show that films doped with excess 1 in both solvents have approximately one SbCl per 33 CH units.     

Molybdenum Substitution for Improving the Charge Compensation and Activity of Li2MnO3

Lithium‐rich layer‐structured oxides xLi₂MnO₃? (1?x)LiMO₂ (0<x<1, M=Mn, Ni, Co, etc.) are interesting and potential cathode materials for high energy‐density lithium ion batteries. However, the characteristic charge compensation contributed by O^2? in Li₂MnO₃ leads to the evolution of oxygen during the initial Li⁺ ion extraction at high voltage and voltage fading in subsequent cycling, resulting in a safety hazard and poor cycling performance of the battery. Molybdenum substitution was performed in this work to provide another electron donor and to enhance the electrochemical activity of Li₂MnO₃‐based cathode materials. X‐ray diffraction and adsorption studies indicated that Mo⁵⁺ substitution expands the unit cell in the crystal lattice and weakens the Li?O and Mn?O bonds, as well as enhancing the activity of Li₂MnO₃ by lowering its delithiation potential and suppressing the release of oxygen. In addition, the chemical environment of O^2? ions in molybdenum‐substituted Li₂MnO₃ is more reversible than in the unsubstituted sample during cycling. Therefore molybdenum substitution is expected to improve the performances of the Li₂MnO₃‐based lithium‐rich cathode materials.     

Some reduced ternary and quaternary oxides of molybdenum. A family of compounds with strong metal-metal bonds

Several new, reduced ternary and quaternary oxides of molybdenum are reported, each containing molybdenum in an average oxidation state <4.0. All are prepared by reactions between a molybdate salt; metal oxide, if needed; and MoO₂ sealed in Mo tubes held at 1100°C for ca. 7 days. Refinement of the substructure of the new compound Ba_0.62Mo₄O₆ was based on an orthorhombic cell, witha = 9.509(2), b = 9.825(2), c = 2.853(1)Å, Z = 2 in space groupPbam; weak supercell reflections indicate the true structure hasc = 8(2.853) Å. The chief structural feature is closely related to that of NaMo₄O₆ (C. C. Torardi, R. E. McCarley,J. Amer. Chem. Soc.101, 3963 (1979)), which consists of infinite chains of Mo₆ octahedral clusters fused on opposite edges, bridged on the outer edges by O atoms and crosslinked by MoOMo bonding to create four-sided tunnels in which the Ba²⁺ ions are located. The structure of Ba_1.13Mo₈O₁₆ is triclinic,a = 7.311(1), b = 7.453(1), c = 5.726(1)Å, α = 101.49(2), β = 99.60(2), γ = 89.31(2)°,Z = 1, space groupP1¯. It is a low-symmetry, metal-metal bonded variant of the hollandite structure, in which two different infinite chains, built up from Mo₄O^2?₈ and Mo₄O^0.26?₈ cluster units, respectively, are interlinked via MoOMo bridge bonding to create again four-sided tunnels in which the Ba²⁺ ions reside. Other compounds prepared and characterized by analyses and X-ray powder diffraction data arePb_xMo₄O₆(x ～ 0.6), LiZn₂Mo₃O₈, CaMo₅O₈, K₂Mo₁₂O₁₉, and Na₂Mo₁₂O₁₉.     

Mechanisms of molybdenum substitution in vanadium antimonate

The formation of a solid solution containing the three elements V, Sb and Mo, which are key-elements in the design of light alkane oxidation catalysts, has been studied by incorporating molybdenum into the pure VSbO₄ compound as obtained in air at 700°C (V³⁺_0.28V⁴⁺_0.64□_0.16Sb⁵⁺_0.92O₄). Monophasic compounds with a rutile-type structure have been obtained and characterized by X-ray diffraction, electron microscopy, Infrared Fourier transform, X-ray absorption and electron spin resonance spectroscopies. At low molybdenum content, Mo⁶⁺ substitute V⁴⁺ in the cationic-deficient structure. The charge balance is maintained by an increase of the cationic vacancy number. This leads to the formation of a solid solution corresponding to the formula V³⁺_0.28V⁴⁺_0.64−3xMo⁶⁺_2x□_0.16+xSb⁵⁺_0.92O₄ with 0<x<0.09. At higher molybdenum content, Mo⁵⁺ are stabilized and substitute Sb⁵⁺ in the rutile structure: V³⁺_0.28V⁴⁺_0.37Mo⁶⁺_0.18□_0.25Mo⁵⁺_ySb⁵⁺_0.9−yO₄ with 0<y<0.06. At higher molybdenum content the rutile phase is no longer stable and two new phases are formed: Sb₂O₄ and a new mixed vanadium molybdenum antimonate.     

Paramagnetic absorption of pentavalent molybdenum in polycrystalline tin dioxide

Part of molybdenum introduced in SnO₂ by various methods is found to be stabilized in the pentavalent state at substitutional positions. The ESR spectra of Mo⁵⁺ ions are characterized by the following parameters: g_xx = 1.891; g_yy = 1.835 and g_zz = 1.923, A_xx = 24 G, A_yy = 30 G and A_zz = 70 G. There are, in addition, two sets of superhyperfine structures due to the two tins located along the crystallographic c axis (290 G) and to the four tins lying in a diagonal plane of the unit cell containing four oxygens (51 G), consistent with a 3d_x²-y² + λ 3d_z2 ground state. The variations of the Mo⁵⁺ ESR spectrum upon heating the samples in various atmospheres (O₂, H₂) suggest that molybdenum enters the SnO₂ lattice also as Mo⁴⁺.