Does an all-sulphur analogue of heptamolybdate exist?

The complexes [MoX₄]²⁻ (M = Mo; X = O or S) exist as the monomeric tetrahedral species in aqueous alkaline solutions. Acidification of tetraoxomolybdate results in the condensation of the tetrahedral units via a series of polyoxomolybdates leading to the ultimate formation of the trioxide MoO₃. Heptamolybdate [Mo₇O₂₄]⁶⁻ is the first major polyanion of the acidification reaction. In contrast, acidification of tetrathiomolybdates leads to the formation of amorphous molybdenum trisulphide via a dinuclear Mo(V) complex. The formation of the dinuclear Mo(V) complex precludes the formation of any higher nuclearity Mo(VI)-S complexes in aqueous solution. Thus it is shown that the all-sulphur analogue of heptamolybdate [M0₇S₂₄]⁶⁻ does not exist in alkaline medium and also cannot be isolated from aqueous acidic medium     

盐酸酸沉四钼酸铵结晶的成核研究

本文研究了用盐酸酸沉仲钼酸铵溶液制备四钼酸铵的成核过程,测量了以诱导期表示的成核速率,讨论了温度和过饱和比对成核速率的影响.结果表明,四钼酸铵过饱和溶液的成核速率随着温度的升高和过饱和比的增大而增大.确定了在实验的温度范围内均匀成核和非均匀成核之间的界限,并根据均匀成核理论计算了其成核特征参数.     

p‐TSA Catalyzed Synthesis of 2,4,5‐Triarylimidazoles from Ammonium Heptamolybdate Tetrahydrate in TBAI

A one‐pot synthesis of 2,4,5‐trisubstituted imidazoles from 1,2‐diketone or α‐hydroxy ketone, aldehyde and ammonium heptamolybdate tetrahydrate in an inexpensive and readily available ionic liquid, tetrabutylammonium iodide (TBAI) in molten state using catalytic amounts of p‐TSA has been described.     

Synthesis and Characterization of a Bismuth Incorporating Heptamolybdate： （NH4）4 [HMo7O24Bi（H2O）2CsH3N（CO2）2]·7H2O

A new one-dimensional molecule based on the linkage of [Mo7024] clusters and [BiL] （L = pyridine-2,6-dicarboxylic acid） assembles under ambient conditions. The title compound was characterized by X-ray powder diffraction, IR and UV spectra, thermogravimetric analysis, and single-crystal X-ray diffraction. Crystal data： C7H38BiMo7N5037, Mr = 1664.95, monoclinic, space group C2/c, a = 24.312（2）, b = 21.4869（18）, c = 18.5423（16） A, β = 111.6490（10）°, V = 9002.9（13） A3, Z = 8, μ = 5.883 mm-1, F（000） = 6304, GOF = 1.045, R = 0.0365 and wR = 0.1062.     

Hydrothermal synthesis and crystal structure of Na(NH4)[C13N2H16]2[Mo7O24]?·?8H2O: A novel 3-D extended supramolecular network with 1-D channels

A novel three-dimensional (3-D) supramolecular assembly of organic bicapped heptamolybdate Na(NH₄)[C₁₃N₂H₁₆]₂[Mo₇O₂₄]·8H₂O has been hydrothermally synthesized and structurally characterized by single-crystal X-ray diffraction, IR spectra, elemental analysis, and thermogravimetric analysis (TGA). X-ray analyses show that compound 1 represent a novel 3-D extended supramolecular “host” networks with 1-D channels encapsulating flexible cation “guests”. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis and Characterization of a Bismuth Incorporating Heptamolybdate:(NH_4)_4[HMo_7O_(24)Bi(H_2O)_2C_5H_3N(CO_2)_2]·7H_2O

A new one-dimensional molecule based on the linkage of [Mo7O24] clusters and [BiL](L = pyridine-2,6-dicarboxylic acid) assembles under ambient conditions. The title compound was characterized by X-ray powder diffraction, IR and UV spectra, thermogravimetric analysis, and single-crystal X-ray diffraction. Crystal data: C7H38BiMo7N5O37, Mr = 1664.95, monoclinic, space group C2/c, a = 24.312(2), b = 21.4869(18), c = 18.5423(16) , β = 111.6490(10)o, V = 9002.9(13) 3, Z = 8, μ = 5.883 mm–1, F(000) = 6304, GOF = 1.045, R = 0.0365 and wR = 0.1062.     

Synthesis of heptamolybdate‐intercalated MgAl LDHs and its application in polyurethane elastomer

Heptamolybdate (Mo₇O₂₄^6?) was intercalated in the interlayer space between MgAl‐layered double hydroxides (Mo‐MgAl LDHs) by the hydrothermal and ion exchange method, and then polyurethane elastomer (PUE) based composites were prepared by the prepolymerization method with different amounts of Mo‐MgAl LDHs. X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectra, laser Raman spectroscopy (LRS), and scanning electron microscopy (SEM) were employed to characterize the obtained LDHs. The performance of the PUE/LDHs were evaluated by measuring their thermal gravimetric, heat release rate (HRR), and smoke density (Ds). The results show that PUE/LDH composites exhibit a lower peak heat release rate (pk‐HRR), Ds, and a prolonged combustion time, in comparison with neat PUE. Comparison between NO₃‐MgAl LDHs and Mo‐MgAl LDHs containing composites show that the introduction of Mo⁶⁺ is able to facilitate flame retardance and smoke suppression efficiency, which results mainly from the presence of MoO₃ derived from the decomposition of Mo₇O₂₄^6? intercalated LDHs. Mo‐MgAl LDHs reduce the pk‐HRR of composites by 39% with only 1 wt.% content, and the maximum Ds of composites is reduced to a minimal value of 274 with 10 wt.% Mo‐MgAl LDHs. More importantly, LDHs would improve the mechanical properties at a low content. The experimental results reveal the potential of Mo₇O₂₄^6? intercalated LDHs to improve both the flame retardancy and smoke suppression of PUE. Copyright © 2015 John Wiley & Sons, Ltd.     

Syntheses and structures of two new lithium-heptamolybdates

The synthesis, crystal structures, IR, UV–vis, ⁷Li NMR spectra, electrochemical investigations, and conductivity studies of two new lithium-heptamolybdates, (NH₄)₄[Li₂(H₂O)₇][Mo₇O₂₄]·H₂O (1) and (NH₄)₃[Li₃(H₂O)₄(μ₆-Mo₇O₂₄)]·2H₂O (2), are reported. In 1 the (NH₄)⁺ and [Li₂(H₂O)₇]²⁺, cations are charge balanced by the heptamolybdate anion. In 2, the [Mo₇O₂₄]^6? anion is coordinated to three unique Li⁺ ions via a μ₆-hexadentate-binding mode resulting in the formation of a two-dimensional (2-D) [Li₃(H₂O)₄(μ₆-Mo₇O₂₄)]^3? anionic complex, charge neutralized by three (NH₄)⁺ ions. The cations, anions, and the lattice water molecules in 1 and 2 are linked by weak H-bonding interactions.     

Effects of alkali metal ions on the thermal decomposition of ammonium heptamolybdate tetrahydrate

The thermal decomposition of pure ammonium heptamolybdate tetrahydrate (AHMT), and doped with Li⁺, Na⁺ and K⁺ ions was investigated using thermogravimetry, differential thermal analysis, infrared and X-ray diffraction techniques. Results obtained revealed that the decomposition of AHMT proceeded in three decomposition stages in which both NH₃ and H₂O were released in all stages. The presence of 0.5 mol % alkali metal ions enhances the formation of the intermediateb (NH₄)₂MO₇O₂₂·2H₂O while the decomposition of this intermediate into MoO₃ is slightly affected in the presence of all dopant concentrations used. The infrared absorption spectra of the thermal products of AHMT treated with 10 mol% alkali metal ions (AMI) at 350°C indicated a reduction of some Mo⁶⁺ ions. By heating of AHMT above 500°C in presence of 5 or 10 mol % of AMI, a solid-solid interaction between alkali metal oxides and MoO₃ giving rise to well crystallized alkali metal molybdates. finally the activation energies accompanied various decomposition stages were calculated.