Oxygen guests

B Champagnon, G Panczer, B Chazallon, L Arnaud, P Duval, V Lipenkov. Nitrogen and oxygen guest molecules in clathrate hydrates different sites revealed by Raman spectroscopy. J Raman Spectrosc 28(9) 711-716, 1997. 

Fig. 14. Choleic acid inclusion chemistry (a) crystal stmcture of DCA inclusion compound with phenanthrene (b) view along a DCA inclusion helix accommodating DMSO and water guest molecules (oxygen and sulfur atoms and methyl groups are represented by open circles and large and small black...

Another related host-guest complex has been constructed from citric acid, boric acid, and a strontium salt in a 2 1 1 stoichiometry. In this complex the strontium cation is surrounded by four water molecules, two monodentate carboxyl groups and one oxygen atom of the BO4 unit [161]. 

Fig. 5. Constitution of a typical hydrate clathrate (tri-n-butylsulfonium ion as guest). The guests are accommodated within H-bond-mediated water polyhedrons (apexes are equivalent to water oxygens) (Adapted from Ref. 6)...

H). As shown, a disordered structural model was obtained for the guest. The model comprises two mirror-related guest molecules. The oxygen atom and the proximal methyl C-atom are practically overlapping the same atomic positions in both orientations. However, the sulphur atomic positions do not average in the X-ray data and show a nearly 50/50 occupancy. As indicated by the comparison of the respective bond distances and intra-associate contact distances of the DMSO molecule (Table 17), the effect of disorder is serious (e.g. the S=0 distances appear abnormally short in the 20 DMSO instance). This precludes the possibility of assessing interaction between the O atom of the carboxyl and a methyl of dimethyl sulfoxide. 

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