Structure and Thermal Transformations of Methylammonium Tungstate

Abstract

Methylammonium paradodecatungstate, (CH3NH3)10[H2W12O42] ⋅ nH2O, was prepared by the reaction of WO3 or H2WO4 in aqueous methylamine, followed by drying. The [H2W12O42]10− anion consists of two HW3O13 groups containing three edge‐sharing WO6 octahedra and two W3O14 groups having two edge‐sharing connections. On drying the produced material at 70 °C, some lattice water was released, but this did not affect the [H2W12O42]10− structure, although there was a decrease in the unit cell volume. By adding water, the loss of lattice water and structural changes were reversed. The existence of paradodecatungstate anions was confirmed by single‐crystal and powder X‐ray diffraction, Fourier transform infrared, Raman, 183W nuclear magnetic resonance, and ultraviolet‐visible spectroscopy. When the methylammonium paradodecatungstate was heated to more than 150 °C, CH3NH2 and H2O were released, and amorphous WO3 was observed as an intermediate product and monoclinic WO3 as the final product. These results reveal the structure of methylammonium tungstate, which was first reported in 1909 and now is used as an important negative staining reagent for virus observation, is methylammonium paradodecatungstate.

Structure Transformation of Methylammonium Polyoxomolybdates via In-Solution Acidification and Solid-State Heating from Methylammonium Monomolybdate and Application as Negative Staining Reagents for Coronavirus Observation

“…In addition to the appearance of H 2 O and CH 3 NH 2 , the degradation and oxidized species of methylammonium such as NH 3 , CO, N 2 , NO, CO 2 , and N 2 O were observed, indicating that a redox reaction between methylammonium and Mo has occurred under inert gas flow. Similar degradation and oxidation reactions of methylamine in methylammonium paradodecatungstate and vanadate under inert gas flow have been observed. , …”

“…Similar degradation and oxidation reactions of methylamine in methylammonium paradodecatungstate and vanadate under inert gas flow have been observed. 22,23 In situ heating powder XRD experiments confirmed that structure transformation occurred during heating (Figure S9). The heating of (CH 3 NH 3 ) 2 [MoO 4 ] (Figure S9a Effect of Countercations on the Polyoxomolybdate Structure Produced by Solid-State Heating.…”

“…We have previously reported that the reaction of WO 3 and V 2 O 5 with the volatile base methylamine (CH 3 NH 2 ) and subsequent drying produced methylammonium paradodecatungstate, (CH 3 NH 3 ) 10 [H 2 W 12 O 42 ], 22 and methylammonium vanadate, CH 3 NH 3 [VO 3 ]. 23 In our previous communication, 24 we reported that dissolving MoO 3 in aqueous methylamine solution produced monomolybdate, [MoO 4 ] 2− , in solution, which could be isolated as methylammonium salt, (CH 3 Preparation of the Single Crystals of Polymeric ((CH 3 NH 3 ) 2 [(MoO 3 ) 3 (SO 4 )]) n .…”

Molar-Ratio-Dependent Coordination Assembly of Organoiridium(III)-Octatungstate Complexes in Aqueous Solution

“…Paratungstate-B is the dominant species in aqueous tungstate solution in a wide pH range and is isolable in the solid state. , The fact that octatungstate instead of paratungstate-B is formed in the presence of {Cp*Ir} 2+ indicates a structure-directing property of {Cp*Ir} 2+ . To test this hypothesis, we carried out a reaction between [(Cp*IrCl) 2 (μ-Cl) 2 ] and methylammonium paratungstate-B (CH 3 NH 3 ) 10 [H 2 W 12 O 42 ]which has a high solubility in wateras the tungsten source. The reaction produced an anionic Cp*Ir–octatungstate complex containing methylamine ligands [(Cp*Ir) 2 {Cp*Ir­(NH 2 CH 3 )} 2 H 2 W 8 O 30 ] 2– ( 4a ) isolated as a methylammonium salt ( 4 ); 4a was also produced by adjusting the pH of a 1:2 [(Cp*IrCl) 2 (μ-Cl) 2 ]/Na 2 WO 4 mixture to 7.5–8.0 by the addition of aqueous methylamine solution from which it crystallized as Na­[(Cp*Ir) 2 (μ-OH) 3 ]­[(Cp*Ir) 2 {Cp*Ir­(NH 2 CH 3 )} 2 H 2 W 8 O 30 ] ( 4′ ).…”

Solid-State 183W NMR Spectroscopy as a High-Resolution Probe of Polyoxotungstate Structures and Dynamics

“…Structural analyses of polyoxometalates have mostly relied on X-ray or neutron diffraction to establish the solid-state structures of compounds that can be isolated and purified, complemented by spectroscopic tools such as multinuclear solution NMR, Raman, and X-ray spectroscopies. , An illustrative example is ammonium paratungstate (APT), [NH 4 ] 10 [H 2 W 12 O 42 ]­(H 2 O) x , which is the prototypical precursor to tungsten-derived materials, including W oxides, W alloys, and W-based catalysts . APT is poorly soluble in water and dissolves predominantly through conversion of the [H 2 W 12 O 42 ] 10– anion (paratungstate B) into the [W 7 O 24 ] 6– anion (paratungstate A), followed by aqueous phase speciation that depends on the pH, temperature, and nature of cations. , Solution 183 W NMR spectroscopy has long been recognized as a powerful tool for analyzing dissolved polyoxotungstates − due to the sensitivity of 183 W chemical shifts to local structures. For instance, for APT and related tungstates, it has been used to establish ion binding sites and the influence of pH and temperature on aqueous speciation .…”