Coupled reaction equilibria enable the light-driven formation of metal-functionalized molecular vanadium oxides

The introduction of metal sites into molecular metal oxides, so-called polyoxometalates, is a key approach to tune their structure and reactivity. To-date, the complex solution mechanisms which govern metal-functionalizatio of polyoxometalates is still poorly understood. Here, we reveal the existence of a coupled set of light-dependent and light-independent reaction equilibria control the mono- and di-metal-functionalization of a prototype molecular vanadium oxide cluster. Comprehensive mechanistic analyses show that coordination of a single Mg2+ ion to the native species (NMe2H2)2[V12O32Cl]3- results in formation of the mono-functionalized system (NMe2H2)[(MgCl)V12O32Cl]3-. This species is photoactive, and irradiation with visible light triggers a second, light-dependent reaction equilibrium which drives the formation of the di-metal-functionalized species [(MgCl)2V12O32Cl]3-. The use cations which compete with Mg2+ can effectively inhibit the formation of the metal functionalized clusters. The study therefore demonstrates how external and internal stimuli can be used to control supramolecular polyoxometalate assembly.