Aggregation of titanium-oxo clusters

Compared with nanoparticle-aspect relatives titanium dioxide (TiO₂), titanium-oxo clusters (TOCs) are atomically structural-determined and can be further precisely modified through coordination and supramolecular chemistry. Another parallel research direction is titanium-based metal-organic frameworks, and those based on TOC have attracted particular attention because of their high optical performances resulting from the cluster aggregation effect. Though challenging, assembling macro-materials from specific clusters helps establish the assembly chemistry of clusters and incorporates porous and flexible characteristics into a single bulk material. Although separate reviews are reported in these two branches, no comprehensive review is available to highlight the bridges between them. Herein, we review and summarize the development and progress of new aggregation of TOCs, from intramolecular unique cluster aggregation to hierarchical intermolecular aggregation via covalent forces, coordination bonds, and non-covalent forces using the specific clusters as precursors. We hope this review fills the gap in the methodology of assembling particular-aggregated TOCs and their derived frameworks, providing general guidance to researchers interested in this area.