Solid state NMR investigations of crystalline organic inclusion compounds

Abstract

The work presented here is concerned with structural and dynamic investigations of crystalline organic inclusion compounds primarily using high-resolution solid state NMR spectroscopy. The focus has been on two types of host systems; urea and tri-ortho-thyirrotide (TOT). High-resolution solid state ¹³C NMR spectra of 1-haloalkane/urea inclusion compounds indicate the existence of two different interactions between end-groups of these guest molecules. This conclusion is derived from the presence of the two signals due to the related end-groups. The chemical shift variation of these signals as a function of the chain length of haloalkanes is reported. A noticeable trend is observed for some of these guest molecules. The areas under these signals are related to the relative numbers of these two interactions. However mathematical analysis shows that it is not possible to derive intrinsic interactions between the end-groups from measurements on these inclusion compounds. It is shown that such information can be obtained via measurement on inclusion compounds containing two types of guest molecules, and then applying the standard results of a Markov chain on these measurements. The migration of the potential guest molecules from the external liquid phase into the tunnel structure of urea inclusion compounds is reported by solid state ¹³C NMR spectroscopy. Several evidence is presented to support the exchange mechanism for this observation. The dynamics of deuterated benzene and pyridine in their TOT inclusion compounds is investigated by variable temperature ²H NMR. These guest molecules are undergoing well defined motion in the solid cage structure. The detailed mechanism of their motions is investigated using computer simulation of the spectra.