Determination of the 17O NMR tensors in potassium hydrogen dibenzoate: : a salt containing a short O⋯H⋯O hydrogen bond

Abstract

Solid-state 17O NMR spectra were obtained at 4.70, 11.75 and 19.60 T for potassium hydrogen [ 17O 4]dibenzoate (PHB) under both magic-angle spinning and stationary conditions. Spectral analyses yielded both the magnitude and orientation of the 17O chemical shift (CS) tensor and the electric field gradient (EFG) tensor for each of the two chemically distinct oxygen sites in PHB. For the oxygen site that is not involved in hydrogen bonding, the experimental 17O NMR tensors are: δ iso=287±2 ppm, δ 11=470±5 ppm, δ 22=380±5 ppm, δ 33=10±5 ppm, C Q=8.30±0.02 MHz, η Q=0.23±0.05, α=0±5°, β=90±5°, and γ=30±5°. For the oxygen site in the short O⋯H⋯O hydrogen bond, the experimental 17O NMR tensors are: δ iso=213±2 ppm, δ 11=370±5 ppm, δ 22=190±5 ppm, δ 33=80±5 ppm, C Q=5.90±0.02 MHz, η Q=0.55±0.05, α=5±5°, β=90±5°, and γ=90±5°. Extensive quantum mechanical calculations at both restricted Hartree–Fock and density functional theory levels were performed to investigate the effects of an effectively symmetrical O⋯H⋯O hydrogen bond on 17O CS and EFG tensors.