Vacancy ordering and host–guest interactions in CdPS3 intercalates: Results from multidimensional solid state NMR

Abstract

Cadmium hexathiohypodiphosphate (CdPS3) intercalates with potassium and N,N′-dimethylviologen cations have been studied by complementary one- and two-dimensional solid state NMR experiments. The intercalation process results in vacancies in the Cd sublattice, whose detailed distribution is sensitively reflected in both the 31P and the 113Cd spectra of the host material. Advanced 2-D 31P double quantum and spin echo NMR techniques are used to further investigate the connectivity patterns of the 31P atoms represented by the peaks observed. Simple chemical shift considerations strongly indicate that the vacancy distribution is primarily controlled by electrostatic repulsion effects. Thus a model is developed for the local vacancy arrangement that links structural motifs with stoichiometry and the NMR results. In the case of the methylviologen intercalate NMR allows the study of the interaction between the organic guest molecule and the host material. Owing to strong Coulombic interactions, one positively charged end of the molecule is pinned at a minimum distance to the negatively charged Cd vacancy in the layer on the NMR time scale, while the other end is orientationally disordered relative to the layers. This arrangement provides an excellent fit to the experimental intensity distributions in the one- and two-dimensional 31P MAS NMR spectra.