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[VV12O32Cl]}3- results in formation of the mono-functionalized {(NMe2H2)[(MgCl)VV12O32Cl]}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)2VIVVV11O32Cl]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. The introduction of metal sites into polyoxometalates is key for tuning their structure and reactivity but the complex mechanisms which govern metal functionalization of polyoxometalates are still poorly understood. Here, the authors 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

Automated summary

In this study, 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 is reported. Mechanistic analyses reveal that coordination of a Mg2+ ion leads to the formation of mono-functionalized compound and release of a placeholder cation. Irradiation with visible light results in one-electron reduction, exchange of the second placeholder cation, and formation/crystallization of the di-metal-functionalized compound. Furthermore, the study demonstrates the feasibility of applying this synthetic concept to other metal cations.