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.

We prepared polyoxomolybdates with methylammonium countercations from methylammonium monomolybdate, (CH3NH3)2[MoO4], through two dehydrative condensation methods, acidifying in the aqueous solution and solid-state heating. Discrete (CH3NH3)10[Mo36O112(OH)2(H2O)14], polymeric ((CH3NH3)8[Mo36O112(H2O)14])n, and polymeric ((CH3NH3)4[γ-Mo8O26])n were selectively isolated via pH control of the aqueous (CH3NH3)2[MoO4] solution. The H2SO4-acidified solution of pH < 1 produced "sulfonated α-MoO3", polymeric ((CH3NH3)2[(MoO3)3(SO4)])n. The solid-state heating of (CH3NH3)2[MoO4] in air released methylamine and water to produce several methylammonium polyoxomolybdates in the sequence of discrete (CH3NH3)8[Mo7O24-MoO4], discrete (CH3NH3)6[Mo7O24], discrete (CH3NH3)8[Mo10O34], and polymeric ((CH3NH3)4[γ-Mo8O26])n, before their transformation into molybdenum oxides such as hexagonal-MoO3 and α-MoO3. Notably, some of their polyoxomolybdate structures were different from polyoxomolybdates produced from ammonium molybdates, such as (NH4)2[MoO4] or (NH4)6[Mo7O24], indicating that countercation affected the polyoxomolybdate structure. Moreover, among the tested polyoxomolybdates, (CH3NH3)6[Mo7O24] was the best negative staining reagent for the observation of the SARS-CoV-2 virus using transmission electron microscopy.

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

We scrutinized the speciation of Cp*Ir-containing tungsten oxide clusters (Cp* is pentamethylcyclopentadienyl anion) in aqueous mixtures of [(Cp*IrCl)2(µ-Cl)2] and Na2WO4 in varying molar ratios. 1H nuclear magnetic resonance (NMR) spectroscopy revealed the formation of three distinct Cp*Ir-polyoxotungstate species in the reaction solution, and they were isolated as Na4[(Cp*Ir)2(µ-OH)3]2[(Cp*Ir)2H2W8O30] (1), [(Cp*Ir)2(µ-OH)3]2[(Cp*Ir)2{Cp*Ir(OH2)}2H2W8O30] (2), and [(Cp*Ir)2{Cp*Ir(OH2)}2{Cp*Ir(OH2)2}2H2W8O30](NO3)2 (3) from the mixtures in which iridium concentration is less than, equal to, and more than the tungsten concentration, respectively. These results show the octatungstate [H2W8O30]10- anion is the major polyoxotungstate species in the presence of {Cp*Ir}2+ cations, and it has high nucleophilicity enough to bind up to six {Cp*Ir}2+ cations on its surfaces producing a cationic Cp*Ir-octatungstate complex. The octatungstate anion was also generated from the reaction of [(Cp*IrCl)2(µ-Cl)2] and methylammonium paratungstate-B, (CH3NH3)10[H2W12O42], and was isolated as a methylamine-coordinated complex (CH3NH3)2[(Cp*Ir)2{Cp*Ir(NH2CH3)}2H2W8O30] (4), indicating {Cp*Ir}2+ cations function as a structure-directing agent that converts tungsten species into octatungstate anions in aqueous solution. In addition, the coordination environment of {Cp*Ir}2+ can be further modified by coordination with pyridine forming [{Cp*Ir(NC5H5)}2(µ-OH)2][(Cp*Ir)2{Cp*Ir(NC5H5)}2H2W8O30] (5).

Thermal Structure Transformation of Methylammonium Vanadate and it's Application as a Negative Staining Reagent for Observing SARS-CoV-2.

The solid-state thermal structure transformation of methylammonium vanadate, (CH3NH3)VO3, from -150 °C to 350 °C is reported. Variable-temperature X-ray single-crystal structure analysis at 23, 0, -50, -100, and -150 °C reveal (CH3NH3)VO3 comprises of methylammonium cations and "snake-like" ([VO3]-)n anion chains propagating along the c-direction in the Pna21 space group. In between -150 and -100 °C, we observe a reversible structural transformation due to the re-orientation of the methylammonium cations in the crystal packing, which is also confirmed by the reversible profiles observed in differential scanning calorimetry. The methylammonium vanadate is stable until at ca. 100 °C and further heating releases methylamine and water and V2O5 is formed at ca. 275 °C . Furthermore, we show that the methylammonium vanadate can be used as a negative staining reagent for visualizing SARS-CoV-2, allowing us to discern the spike proteins from the body of the virus using transmission electron microscopy.