Synthetic strategies, diverse structures and tuneable properties of polyoxo-titanium clusters

As one of the most prosperous classes of cluster-based materials reported to date, polyoxo-titanium clusters (PTCs) have been closely related to many photo-activities that broadly impact not only chemical but also energy and environmental sciences. In contrast to the well-developed polyoxometalates like polyoxotungstates and polyoxomolybdates, there is still large room for the development of PTCs. The exploration of crystalline PTC materials originates from the molecular model of technically important TiO₂ materials but has been greatly hindered by their daunting and challenging synthesis. This review firstly summarizes the conventional and latest successful synthetic strategies applied to improve the poor degree of control of crystallization of PTCs. And attributed to the synthetic progress achieved in this area, there is a growing number of PTCs with diverse structures known to us, also enabling us to study their bandgap engineering and light absorption behaviours at the molecular level. In addition, exploitation of their applications in many fields is also under way.