1H- 31P CPVC NMR method under Very Fast Magic Angle Spinning for analysis of dipolar interactions and dynamics processes in the crystalline phosphonium tetrafluoroborate salts

摘要

AbstractWe present an NMR methodology which can be used to study the dynamical processes occurring in organophosphorus compounds that belong to the group of the organic ionic plastic crystals (OIPCs). As model samples we employed two phosphonium tetrafluoroborate salts; (t-Bu)3PH+BF4?(1) and (Me)3PH+BF4?(2). Both samples possess in their structures direct H-P bonds, and both undergo complex thermal processes in the solid state, forming below the melting point three or four phases, respectively.1H-31P CPVC (Cross-Polarization Variable Contact) measurements were performed under Very Fast Magic Angle Spinning with speed equal to 50 or 60?kHz, in order (i) to establish the hydrogen-phosphorus dipolar couplings, and (ii) to correlate the dipolar splitting values with molecular motions of the cation.Our project is divided into three sections. In the first part we present DSC studies of (1) and (2), to verify whether these samples fulfill the requirements that define them as OIPC. The second part is dedicated to a discussion of the theoretical aspects of1H-31P CPVC and especially an analysis of the influence of different parameters, e.g. CSA31P, H-H mismatch, rf-inhomogeneity, dipolar truncation, and the type of dynamics through the motionally averaged <ηD1H-31P CPVC data and applicability of these measurements to study H-P distances and dynamics. The complex molecular motion for sample (2), including rotation and diffusion, versus temperature is then postulated on the bases of the changes of H-P dipolar splitting.Graphical abstractDisplay OmittedHighlights?We have tested CPVC sequence under MAS conditions at 50 and 60?kHz for measure of31P1H dipolar interactions.?On the ground of theory we have analyzed the influence of imperfections on quality of NMR data.?We have studied dynamics processes in the crystalline phosphonium tetrafluoroborate salts (PTS).?E