A molecular placeholder strategy to access a family of transition-metal-functionalized vanadium oxide clusters.

Systematic access to metal-functionalized polyoxometalates has thus far been limited to lacunary tungsten oxide and molybdenum oxide clusters. The first controlled, stepwise bottom-up assembly route to metal-functionalized molecular vanadium oxides is now presented. A di-vacant vanadate cluster with two metal binding sites, (DMA)2V12O32Cl (DMA = dimethylammonium) is formed spontaneously in solution and characterized by single-crystal X-ray diffraction, ESI mass spectrometry, (51)V NMR spectroscopy, and elemental analyses. In the cluster, the metal binding sites are selectively blocked by hydrogen-bonded DMA placeholder cations. Reaction of the cluster with transition metals TM (Fe(3+), Co(2+), Cu(2+), Zn(2+)) gives access to mono-functionalized vanadate clusters (DMA){TM(L)}V12O32Cl (L = ligand). Metal binding is accomplished by significant distortions of the vanadium oxide framework reminiscent of a pincer movement. Cluster stability under technologically relevant conditions in the solid-state and solution is demonstrated.