Multiple resonance heteronuclear decoupling under MAS: Dramatic increase of spectral resolution at moderate magnetic field and MAS frequencies

Abstract

The effects of multiple-resonance heteronuclear decoupling under magic angle spinning (MAS) on the resolution of one-dimensional 19F and 31P and various two-dimensional MAS NMR spectra and on the residual non-refocusable coherence lifetimes in fluorinated aluminophosphate AlPO 4-CJ2, i.e. a compound that contains numerous highly abundant nuclei but no homonuclear spin bath, has been investigated. The design of the four-channel ( 1H, 19F, 27Al, 31P) MAS probe used for this study is first described. 1H and 1H– 27Al double-resonance decouplings allows lengthening the optimized transverse relaxation T 2 opt and increasing the resolution in the 19F and 31P dimensions. Under the application of multi-nuclear decoupling, a two-dimensional 19F– 31P CP-HETCOR correlation spectrum for AlPO 4-CJ2 is recorded with unprecedented high-resolution in the two dimensions. Moreover, because 1H-decoupling increases the 19F T 2 opt , it has been applied during the entire duration of the 2D NMR experiments, allowing the direct use of residual small interactions to generate 19F– 19F and 19F– 27Al 2D NMR correlation spectra in AlPO 4-CJ2.