Double cross-polarization MAS NMR in the assignment of abundant-spin resonances: 19F–{29Si}–19F FBCP/MAS NMR of fluoride ions incorporated in calcium silicate hydrate (C–S–H) phases

[Display omitted] ► A new version of the double-cross polarization NMR experiment: Forth and Back CP. ► Detection of the high-γ spins for assignment of resonances for these abundant spins. ► Experimental demonstration by 19F–{29Si}–19F and 19F–{13C}–19F FBCP/MAS NMR spectra. ► Assignment of 19F resonances for fluoride in calcium silicate hydrate (C–S–H) phases. A new version of the double cross-polarization MAS NMR experiment, which transfers polarization Forth and Back (FBCP) between high- and low-γ spin nuclei, is presented. The pulse sequence is demonstrated by 19F–{29Si}–19F and 19F–{13C}–19F FBCP NMR spectra of a mixture of cuspidine (Ca4Si2O7F2) and Teflon (–CF2–)n. The experiment is useful for assignment of the high-γ spin resonances, as demonstrated by 19F–{29Si}–19F FBCP NMR of a fluoride-containing calcium–silicate–hydrate (C–S–H) phase, where the 19F resonance from fluoride ions incorporated in the interlayer structure of the C–S–H phase is identified.