The relationship between molecular structures of quaternary ammonium cations and the combined cages which can be stabilized by the cations is shown in Fig. , e.g., well symmetric ions such as tetra-n-butylammonium (TBA or N4444) (34) and tetra-i-pentylammonium (Ni5i5i5i5) and partly asymmetric tri-n-butyl, n-pentylammonium (N4445) (41) cations, where in abbreviation N, 4, 5, i5 denote nitrogen, n-butyl, n-pentyl, i-pentyl, respectively. The nhexyl chain is the only guest that can stabilize the true form of the P cage with the 6 � m2 symmetry required for the HS-I structure, which has never been stabilized by the other guests. The distortions in the hydrogen bonds of the water molecules in these structures are caused by incorporation of the cations, especially in the hexagonal faces of the P cage in the true form to be the distorted form (P' cage). The present results found that n-butyl and i-pentyl chains are not large enough to stabilize the P cage which has an ideally symmetric shape. In other words, such minute size difference in hydrophobic part, e.g., n-hexyl and n-butyl, may determine the whole structure of the clathrate hydrates. In Fig. , the ID' 2 cage of the HS-III structure, which is one of the three major structures of clathrate hydrates, was together shown, where D' cage is 4 3 5 6 6 3 the 4 denotes square face. The I cage is the combined T 2 cage, which also absorbs a part of the P cage space which were sandwiched between the T 2 cage from the perspective of the direction perpendicular to the hexagonal face of the T cage. As a result, the D' cage takes the shape of the part of the original P cage that was shaved off by the I cage. When the I cage can be stabilized by occupancy of a large molecule such as 2,2-Dimethylbutane, the HS-III structure forms, but to support HS-III structure, guest gas occupancy in the D and the D' cages are necessary. Since CO2 inclusion in the HS-III structure has been unclear even under support by CH4 , CO2 seems to be unpreferable guest for the D' cage which is required to support this HS-I derived structure. In the present HS-I structure, since the truly formed P cage was stabilized by the cation, CO2 is not required to occupy the D' cage, but only the D cage.