Record-large indium-oxo clusters: synthesis, hierarchical assembly, and efficient optical limiting

High-nuclearity indium-oxo clusters (InOCs) represent critical molecular models for understanding indium oxide (In₂O₃) nanoparticles, yet their rational synthesis remains a formidable challenge. Herein, we report a dual-ligand strategy to access bixbyite-type In₁₅-oxo clusters-the largest discrete indium-oxo cores reported to date. Their strategically labile carboxylate sites enable facile functionalization to generate InOC-38, InOC-39, and InOC-40. Notably, the In₁₅ core serves as the highest-nuclearity secondary building unit (SBU) within the InOC family, which can be extended into an In₃₀ dimer (InOC-41) via a cluster-docking strategy or hierarchically assembled into one-dimensional chains (InOC-42) using multidentate 6-hydroxynicotinate linkers. These architectures, featuring π-conjugated ligands, heavy metals, and dense intermolecular interactions, exhibit exceptional optical limiting (OL) performance. InOC-38 and InOC-41 demonstrate record metrics (T _min = 0.11 and 0.17; F _OL = 0.275 and 0.408 J cm^-2), surpassing state-of-the-art cluster-based materials. Furthermore, their processability into flexible transparent films underscores significant practical potential for optical applications.