XE-129 NMR-STUDIES OF CLATHRATE HYDRATES - NEW GUESTS FOR STRUCTURE-II AND STRUCTURE-H

A 129Xe NMR technique was developed to assess the clathrate hydrate forming ability of new potential guest molecules and to determine the structure of the resulting hydrates. About 25 new guests, mainly hydrocarbons, were identified as stabilizing the recently reported hexagonal hydrate, structure H. Successful tests of a few guests with different functional groups show that structure H represents a large new family of hydrate structures. New structure II hydrate formers include the first examples of ester and nitrile guests. It is shown that guests with maximum dimension larger than ∼7.1 Å A require the presence of a help gas to give a stable structure II hydrate and that guests larger than 7.5 Å, together with a suitable help gas, promote structure H. In addition to correct size, the guest molecule is required to have the correct shape for efficient space filling of the structure H large cage. © Published 1990 by the American Chemical Society.