Understanding the vibrational and electronic features of Ti(IV) sites in mesoporous silicas by integrated ab initio and spectroscopic investigations

Structural and spectroscopic investigations on Ti(IV) centers in different mesoporous silicas are carried out by an integrated experimental and theoretical approach. The combined study has allowed us to highlight many features of the tripodal ((OH)Ti(OSi)3) or tetrapodal Ti(OSi)4 Ti(IV) sites present in the silica matrix, the concentration of which may depend on the synthetic approach adopted to obtain the mesoporous Ti(IV)-SiO2 materials. The study of the effect of silylation on the catalysts and the model systems has allowed us, for the first time, to clarify relevant microscopic details of silylated Ti(IV) sites in mesoporous silicas. Ti(IV) centers are found in a tetrahedral arrangement independently on the tripodal, tetrapodal, or silylated structure, and their spectroscopic features are found to be tuned by the silica matrices.