Sprayed Microdroplets Architect a Polyoxometalate Framework

Abstract

Although many past attempts have utilized micron-sized droplets for breaking and forming organic bonds, their potential in promoting inorganic bond formation reactions remains largely unexplored. We report a promising approach to synthesizing a tungsten-based Lindqvist-type polyoxometalate (POM) in various organic and aqueous microdroplets under ambient conditions, eliminating the traditional need for hazardous or corrosive chemicals and high-boiling solvents. When aerosolized, a simple tungstate (WO₄ ^2-) solution spontaneously produces a metal-oxo cluster (W₆O₁₉ ^2-), a valuable POM with broad applications, achieving yields up to 99% in less than a millisecond. Mass spectrometric detection of reactive intermediates unraveled the nucleation mechanism in microdroplets, leading to the formation of polyoxotungstate, which was then further characterized by X-ray crystallography. Empirical observations collectively suggest that rapid solvent evaporation and subsequent enrichment of reactants in the confined volume of microdroplets likely facilitate the growth of the POM through partial solvation at the air-liquid interface.

Keywords: Air–liquid interface; Microdroplet chemistry; Polyoxometalate; Rapid nucleation; Unusual reaction.