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 key for tuning their structure and reactivity. The complex mechanisms which govern metal-functionalization of polyoxometalates are still poorly understood. Here, we report a coupled set of light-dependent and light-independent reaction equilibria controlling the mono- and di-metal-functionalization of a prototype molecular vanadium oxide cluster. Comprehensive mechanistic analyses show that coordination of a Mg²⁺ ion to the species {(NMe₂H₂)₂[V^V₁₂O₃₂Cl]}^3- results in formation of the mono-functionalized {(NMe₂H₂)[(MgCl)V^V₁₂O₃₂Cl]}^3- with simultaneous release of a NMe₂H₂⁺ placeholder cation. Irradiation of this species with visible light results in one-electron reduction of the vanadate, exchange of the second NMe₂H₂⁺ with Mg²⁺, and formation/crystallization of the di-metal-functionalized [(MgCl)₂V^IVV^V₁₁O₃₂Cl]^4-. Mechanistic studies show how stimuli such as light or competing cations affect the coupled equilibria. Transfer of this synthetic concept to other metal cations is also demonstrated, highlighting the versatility of the approach.