¹³C/¹⁹F high-resolution solid-state NMR studies on layered carbon-fluorine compounds

Abstract

¹³C/¹⁹F high-resolution solid-state NMR was applied to examine local structures of a stage-1 layered carbon-fluorine compound (C₂.₈). Four ¹⁹F(F1∼F4) and two ¹³C signals (C1 and C2) unraveled by high magnetic field (14 T) and fast magic-angle spinning (>35 kHz) were examined by various two-dimensional correlation experiments. In addition to “through space” ¹³C-¹⁹F and ¹⁹F-¹⁹F dipolar correlation, which reveals distance proximity among ¹³C/¹⁹F spins, we examined feasibility of applying the J interaction for examination of “through bond” correlation. These experiments led assignment of two of the four F signals (F2 and F3) to F directly covalent bonded to sp³ carbon and an interleaving domain for the local structure of the minor C2-F3 group among the major domain composed of C2-F2 and sp² carbon (C1). The other two ¹⁹F signals (F1 and F4) were assigned to as CF₂ and F ions, respectively. A spectroscopic evidence for the C-F bond being the σ bond is given by the observation of a non-zero one-bond J value (193 ± 4 Hz) for C2-F. Further, the similar JCF = 197 Hz for C-F in poly(carbon fluoride) confirmed that the so-called “semi-ionic/semi-covalent” C-F bond in C₂.₈F is actually a “standard” covalent C-F bond.