Kinetic Precipitation of Solution‐Phase Polyoxomolybdate Followed by Transmission Electron Microscopy: A Window to Solution‐Phase Nanostructure

Abstract

This study aimed to elucidate the structural nature of the polydisperse, nanoscopic components in the solution and the solid states of partially reduced polyoxomolybdate derived from the {Mo₁₃₂} keplerate, {(Mo)Mo₅}₁₂‐{Mo₂ acetate}₃₀. Designer tripodal hexamine‐tris‐crown ethers and nanoscopic molybdate coprecipitated from aqueous solution. These microcrystalline solids distributed particle radii between 2–30 nm as assayed by transmission electron microscopy (TEM). The solid materials and their particle size distributions were snap shots of the solution phase. The mother liquor of the preparation of the {Mo₁₃₂} keplerate after three days revealed large species (r=20–30 nm) in the coprecipitate, whereas {Mo₁₃₂} keplerate redissolved in water revealed small species (3–7 nm) in the coprecipitate. Nanoparticles of coprecipitate were more stable than solids derived solely from partially reduced molybdate. The TEM features of all material analyzed lacked facets on the nanometer length scale; however, the structures diffracted electrons and appeared to be defect‐free as evidenced by Moiré patterns in the TEM images. Moiré patterns and size‐invariant optical densities of the features in the micrographs suggested that the molybdate nanoparticles were vesicular.