A Clathrate Hydrate of Nitric Oxide

A somewhat surprising structural type was determined by X‐ray diffraction for the clathrate hydrate of NO: unlike CO, a molecule with very similar properties, NO forms a clathrate hydrate of structural type II, which hitherto had only been encountered for larger molecules (van der Waals radius > 5.8 Å) and nonpolar small molecules like N 2 and O 2 . Thus, further study is required to establish the criteria that determine the structure type of clathrate hydrates.