Polyoxometalate functionalization by light-dependent coupled reaction equilibria

Metal functionalization of molecular metal oxides, so-called polyoxometalates (POMs), is key to control their structure and function. To-date, the chemical reactions underlying these complex processes are still not well understood.
Polyoxometalate functionalization by light-dependent coupled reaction equilibria

Here, we report a coupled set of light-dependent and light-independent reaction equilibria which control the mono- or 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+ cation. Irradiation of this species with visible light results in one-electron reduction of the cluster shell, 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.

Left: Illustration of the di-Mg-functionalized polyoxovanadate species {Mg2V12}.
Right: Illustration of the light-independent and light-dependent coupled reaction equilibria.

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