Strategies for extracting NMR parameters from [formula omitted] MAS, DOR and MQMAS spectra. A case study for Na 4P 2O 7

Abstract

The 23 Na magic-angle spinning (MAS), double rotation (DOR) and multiple-quantum magic-angle spinning (MQMAS) NMR spectra of anhydrous sodium pyrophosphate, Na 4P 2O 7, measured at five different Larmor frequencies ( ν L) ranging from 105.8 MHz (corresponding to 400 MHz 1 H frequency) to 211.6 MHz (800 MHz) are analysed and the complete set of NMR parameters ( C qcc, η Q and δ iso) of the four crystallographically inequivalent sodium sites were determined with high accuracy. Different approaches of spectra evaluation are discussed and their results are compared. The most reliable results are obtained from a combined evaluation of five DOR and three MQMAS spectra but also from two DOR and one MAS spectra or even from a single MQMAS spectrum all data can be derived. It is shown that Na 4P 2O 7 may serve as a useful reference material for experimental set-up and reliability tests of the various NMR experiments.