Application of the Carr-Purcell Meiboom-Gill pulse sequence for the acquisition of solid-state NMR spectra of spin-1/2 nuclei

The quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) pulse sequence has received much attention in the recent literature for use in the rapid acquisition of solid-state NMR spectra of half-integer quadrupolar nuclei. Herein we investigate the application of the CPMG pulse sequence to enhance the signal-to-noise ratio in the static NMR spectra of spin-1/2 nuclei. CPMG is coupled with techniques such as cross-polarization (CP) and two-pulse phase-modulated (TPPM) proton decoupling. The CPMG and CP/CPMG pulse sequences are applied to a series of different NMR nuclides, including Cd-113, Hg-199, Pb-207, N-15 and Ag-109. Standard Cd-113 CP/MAS, MAS and static NMR spectra of Cd(NO3)(2)(.)4H(2)O are compared with corresponding Cd-113 CPMG and CP/ CPMG NMR spectra. Piecewise-acquired wide-line CPMG Hg-119 and Ph-117 NMR spectra of (CH3COO)(2)Hg and (CH3COO)(2)Pb(.)3H(2)O, which are so broad that they cannot be uniformly excited by a single short pulse, reveal that chemical shielding tensor parameters can be determined from these rapidly acquired spectra more accurately than with corresponding CP/MAS spectra. CP/CPMG NMR is also applied to acquire NMR spectra of low-gamma nuclei such as N-15 in (NH4)-N-15 (NO3)-N-15 (98%-enriched) and Ag-109 in AgSO3CH3. The signal obtained from CPMG NMR experiments on stationary samples is comparable to corresponding MAS spectra and much higher than for conventional static NMR spectra, providing an interesting alternative for investigating spin-1/2 nuclei with broad powder patterns.