High-resolution solid-state NMR of phosphorus-fluorine compounds

Abstract

The significance of NMR for chemists is based on the highly specific relations between the observable NMR parameters chemical shift δ (or magnetic shielding σ) and spin-spin coupling J and the electronic environment of the resonance nucleus. The directionality of covalent bonds causes aniso- tropies of σ and J described by the tensors σ ii and J ii. Due to the rapid reorientation of molecules in liquid phases only the popular isotropic mean values σ and J can be observed. In contrast to this ‘degenerate case’ [1] the up-to-date high-resolution NMR in solids provides exact tensor data and therefore gives fundamental new answers to old questions. Using high magnetic fields (B o = 6.4 T) in combination with magic angle sample spinning we measured the 31P shielding ( σ , Δσ, η σ ) and coupling ( J , ΔJ, η J = 0) tensor data for monofluorophosphates. ▪ The data reflect bonding and symmetry of the PO 3F groups as well as the non-equivalence of the P atoms in the dimeric anion. Comparison with condensed phosphates ( cf. table) shows the correspondence of the ligand atoms fluorine and bridging oxygen.