Whereas our predicted structures show good agreement with experimental vibrational shifts, they should be viewed as estimates to what may be more complex in nature. A relevant analogy are the H2O:guest ratios found in low pressure clathrate hydrate phases, which can be as high as 134:24 (structure-II) (2). Despite ruling out thousands of structures on the grounds of energy and a smaller selection based on frequencies, we cannot conclusively predict if the favored ground state structure type is intercalated or layered (Table ). The fact that both structure types agree with observed red-and blue-shifts in the same range of stoichiometry is not unreasonable given the nonspecificity of the HCN-ethane intermolecular interaction.