Quantitative Dynamics and Structure for Crystalline Cs2WO4 and KMnO4 Determined from High-Field 17O Variable-Temperature MAS NMR Experiments

Abstract

High-field (21.15 T), low variable-temperature (VT) 17O MAS NMR spectra of the two tetraoxoanions WO42– and MnO4– in Cs2WO4 and KMnO4, respectively, exhibit highly resolved and quite complex features compared with their singlet appearances observed at room temperature. This study reports some interesting results on the high rotational molecular dynamics for the WO42– and MnO4– anions in the crystalline state for Cs2WO4 and KMnO4 determined from low VT 17O MAS experiments at 21.15 T. 17O exchange times have been determined from a series of 17O exchange spectroscopy (1D/2D EXSY) MAS NMR experiments at a variety of low temperatures and with observed exchange times in the range 0.29–233 ms. Activation energies Ea = 60 ± 2 kJ/mol for the WO42– anion and Ea = 7.3 ± 0.5 kJ/mol for the MnO4– anion in Cs2WO4 and KMnO4, respectively, have been determined from Arrhenius plots of these 17O exchange data.