Solid state NMR and molecular modelling of the p-xylene adduct of Dianin's compound

Abstract

The p-xylene adduct of Dianin's compound was studied by solid state NMR and molecular modelling. Molecular potential calculations were performed considering a p-xylene guest molecule in a single host cage. These calculations confirmed the existence of six different possible orientations of the guest molecules in the cage. The orientations correspond to two types of guests, which are not related by any symmetry, each consisting of three C3 symmetry related sites. The two types induce significant distortions to the local structure of the host crystal cage, and these are most pronounced at the bottle-neck of the cage. In the calculations no diffusion paths were found that transferred guest molecules of one type to the other. X-Ray studies confirmed that the dimensions of the p-xylene/Dianin's cages are essentially equal to those reported previously. In our case, the R3 space groups failed to describe the X-ray diffraction data accurately. Single crystal 2H-NMR of the p-xylene/Dianin's compound, specifically deuterated in the hydroxyl groups of the cage, provided detailed information on the distortions of the hexagons of hydroxyl groups interconnecting two cages. The hexagon distortions were correlated to the orientation of the guest molecules. 13C CP-MAS NMR confirmed that the methyl groups of the host, in the middle of the cage, are influenced strongly by the inclusion of the p-xylene molecules. Based on the experimental observations, a model describing the distortions in the crystal is proposed.