Structural Fluxionality of Surface Motifs in Positional Isomeric Au14Cd2 Clusters Enables Switchable O-O Bond Activation Pathways.

The construction of positional isomers enables tunable control over the physicochemical properties of nanoclusters. However, up to now, the packing model of the core and motif has typically been one-to-one. Herein, we present positional isomeric nanoclusters, Au14Cd2-1 and Au14Cd2-2, which feature an identical Au13 icosahedral kernel but differ exclusively in their surface motif arrangements, leading to distinct electronic distributions. This inherent structural fluxionality enables their reversible interconversion mediated by boranes. Capitalizing on distinct metal charge distributions of the isomers, we employed styrene oxidation (highly sensitive to metal valence states) as a mode to probe their catalytic performance. The results show that the electron-deficient Au14Cd2-1 achieves high conversion (93.1%) with epoxide selectivity (77.3%), whereas the electron-rich Au14Cd2-2 gives lower conversion (36.8%) but high benzaldehyde selectivity (88.9%). Mechanistic interrogation via TEMPO/TPP trapping of key intermediates revealed pathway bifurcation: Au14Cd2-1 follows heterolytic O-O cleavage (metal-oxo pathway), while Au14Cd2-2 undergoes homolytic cleavage (radical pathway). Furthermore, DFT calculations, together with XPS and NMR experiments, revealed stronger styrene binding affinity of Au14Cd2-1, consistent with its higher conversion. This work establishes positional isomerism as an effective strategy to decouple activity and selectivity through independent modulation of substrate binding and O-O bond activation.