The targeted synthesis of single site vanadyl species on the surface and in the framework of silicate building block materials

A new synthetic methodology for the targeted preparation of single site, atomically dispersed vanadyl groups in silicate matrices is described. This methodology requires functionalized silicate building blocks Si₈O₂₀(OSnMe₃)₈ that become linked together through vanadyl (≡VO) groups in the matrix. A sequential addition strategy is illustrated which allows the targeting of specific connectivities for the vanadyl group to the silicate building block matrix (i.e. the number of V–O–Si bonds linking the vanadyl unit). Silicate matrices containing exclusively 3-connected (OV(OSi_cube)₃), 2-connected (OV(OR)(OSi_cube)₂) or 1-connected (OVCl₂(OSi_cube)) vanadyl sites are described and characterized via a wide variety spectroscopic and physical techniques (gravimetric analysis, EXAFS, AA and solid state NMR (⁵¹V, ²⁹Si, and ¹⁷O)). We demonstrate how the combination of gravimetric, solid state NMR (SSNMR) and EXAFS data can be used to uniquely define the vanadyl sites in these matrices. Furthermore, the use of ¹⁷O SSNMR (1D and MQMAS) is illustrated as an indirect spectroscopic probe to follow changes in the ligands bound to vanadium atom within the vanadyl groups in these matrices.