Measurement of indirect spin—spin coupling constants between crystallographically equivalent nuclei. Determination of 2J(31P, 31P) in solid Ag[P(m‐tolyl)3]2NO3

Abstract

AbstractSolid‐state 31P magic angle spinning (MAS) NMR spectra of Ag[P(m‐tolyl)3]2NO3 were investigated as a function of the magic angle spinning frequency. Examination of the 31P MAS NMR spectra obtained at 4.70 and 9.40 T indicates that the two phosphorus nuclei have identical isotropic chemical shifts, that is, they are crystallo‐graphically equivalent, δ = 11.2 ppm. However, since the orientation of their respective chemical shift tensors is not coincident, the two phosphorus nuclei are magnetically non‐equivalent and exhibit spinning‐frequency dependent 31P NMR lineshapes. Analysis of the spinning‐frequency dependent 31P MAS NMR spectra at 4.70 and 9.40 T indicates that 2J(31P, 31P) = 140 Hz. This value was confirmed by 2D J‐resolved spectroscopy. The determination of an indirect spin‐spin coupling constant between two nuclei which constitute an ‘isolated’ spin pair with identical isotropic chemical shifts is not possible in conventional solution‐state NMR studies unless a third spin is introduced. The 31P MAS NMR spectra of Ag[P(m‐tolyl)3]2NO3 also exhibit resolvable splittings due to 109Ag and 107Ag; 1J(109Ag, 31P) = 517±5 Hz and 1J(107Ag, 31P) = 453 ± 5 Hz. In solution NMR studies these couplings are not always observed because of rapid metal‐ligand exchange.