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 [Bi38O45] core. Upon dissolution of crystalline [Bi$_6$O$_5$(OH)$_3$(NO$_3$)$_5$]⋅3 H$_2$O in DMSO, an intermediate rapidly forms, which slowly grows to stable [Bi$_{38}$O$_{45}$] clusters. To

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... entify the intermediate, we developed an automated modeling method, where smaller [BixOy] structures based on the [Bi$_{38}$O$_{45}$] framework are tested against the data. [Bi$_{22}$O$_{26}$] 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.