SOLID-STATE SI-29 MAS NMR-STUDY OF TITANOSILICATES

The relationship among the Si-29 NMR chemical shift, the number of tit anium polyhedra coordinating each silicon tetrahedron, and the oxygen formal charge is examined for titanosilicates with known crystal struc tures. A systematic downfield chemical shift is observed when increasi ng numbers of titanium polyhedra coordinate a given silicon tetrahedro n, which is similar to the trend seen for aluminosilicates. The chemic al shift increases linearly with increasing oxygen formal charge for b oth titanosilicates and aluminosilicates. Summation of the oxygen form al charge accounts for effects on the chemical shift from coordination geometry, nonbridging oxygen, and cation valence. Silicates with a hi gh oxygen formal charge, or more than one nonbridging oxygen per silic on, deviate from the linear trend observed for aluminosilicates and ti tanosilicates. The chemical shift/structure correlations derived from titanosilicates with known crystal structures are used to determine th e local bonding configurations for a new titanosilicate, CsTiSi2O6.5, and for an Engelhard formulation designated ETS-4.