Various vanadium-oxide clusters are exhibited and their spontaneous formation in solution is rationalized. Unlike organic chemistry that is governed by the formation of covalent bonds, inorganic-oxide molecules are dynamic species due to their flexible ionic bonds and have an exquisite beauty showing a spectrum of beautiful colours arising from various coordination modes and valence states. In a catalytic reaction using a vanadate source, vanadium-oxide clusters are often formed and transformed – it is also easy to restore the structure back to the original form. The relative easiness of the transformation in a different structure of blocks, tubes, bowls, cages, spheres and rings is key to understanding each catalytic process. The analogy between the graphite structure and the V2O5 stacked-2D-sheet structure explains the formation of tubes and spheres and is reminiscent of the discovery of nano-tubes and fullerenes in carbon chemistry. Vanadium chemistry enjoys an easiness of modification and incorporation of a guest molecule that it can feasibly control compared to the stubborn fullerene host–guest complex.

The chemistry of inorganic bowl-type host with a future perspective is described as a review of chemistry in 2019 on 化学, Kagakudojin publisher.

The chemistry between polyoxovanadates as a ligand and polycations as a metal cation defines a new class of heteropolyoxovanadates and provides an example of all-inorganic coordination chemistry of a well-defined soluble species. Another examples are reduced polyoxovanadates. For example, reduced-tridecavanadate shown in the left figure forms a dimer connected by 8 hydrogen bonds with reversible redox chemistry.

The condensation reactioin of polyoxovanadates by reductive or oxidative coupling reaction is described and a fundamental IR and UV data are provided in this book.