JMR: Larsen: 47Ti and 49Ti at high fields

Journal of Magnetic Resonance
Volume 178, Issue 2 , February 2006, Pages 228-236

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

Flemming H. Larsen a, Ian Farnan b and Andrew S. Lipton c

aDepartment of Food Science, Quality and Technology, The Royal Veterinary and Agricultural University, Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark
bDepartment of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK
cWilliam R. Wiley, Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Mail Stop K8-98 Richland, WA 99352, USA

Received 20 August 2005; revised 1 October 2005. Available online 2 November 2005.

Abstract

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.

Keywords: QCPMG; Solid state; Isotope-selective; Ti; Multiple fields