Structural Changes during the Growth of Atomically Precise Metal Oxido Nanoclusters from Combined Pair Distribution...

The combination of in situ pair distribution function (PDF) analysis and small-angle X-ray scattering (SAXS) enables analysis of the formation mechanism of metal oxido nanoclusters and cluster-solvent interactions as they take place. Herein, we demonstrate the method for the formation of clusters with a [Bi₃₈ O₄₅ ] core. Upon dissolution of crystalline [Bi₆ O₅ (OH)₃ (NO₃ )₅ ]⋅3 H₂ O in DMSO, an intermediate rapidly forms, which slowly grows to stable [Bi₃₈ O₄₅ ] clusters. To identify the intermediate, we developed an automated modeling method, where smaller [Bi_x O_y ] structures based on the [Bi₃₈ O₄₅ ] framework are tested against the data. [Bi₂₂ O₂₆ ] was identified as the main intermediate species, illustrating how combined PDF and SAXS analysis is a powerful tool to gain insight into nucleation on an atomic scale. PDF also provides information on the interaction between nanoclusters and solvent, which is shown to depend on the nature of the ligands on the cluster surface.