Separation of 47Ti and 49Ti solid-state NMR lineshapes by static QCPMG experiments at multiple fields

Experimental procedures are proposed and demonstrated that separate the spectroscopic contribution from both 47Ti and 49Ti in solid-state nuclear magnetic resonance spectra. These take advantage of the different nuclear spin quantum numbers of these isotopes that lead to different 'effective' radiofrequency fields for the central transition nutation frequencies when these nuclei occur in sites with a significant electric field gradient. Numerical simulations and solid-state NMR experiments were performed on the TiO2 polymorphs anatase and rutile. For anatase, the separation of the two isotopes at high field (21.1 T) facilitated accurate determination of the electric field gradient (EFG) and chemical shift anisotropy (CSA) tensors. This was accomplished by taking advantage of the quadrupolar interaction between the EFG at the titanium site and the different magnitudes of the nuclear quadrupole moments (Q) of the two isotopes. Rutile, having a larger quadrupolar coupling constant (CQ), was examined by 49Ti-selective experiments at different magnetic fields to obtain spectra with different scalings of the two anisotropic tensors. A small chemical shielding anisotropy (CSA) of −30 ppm was determined.