Clathrates different classes

Several exciting new material based on co-crystalline and nanoporous crystalline phases of syndiotactic polystyrene have been achieved. In particular, several kinds of polymer co-crystalline phases have been prepared, belonging to three different classes 8- and e-clathrates and intercalates. Polymer cocrystals with active guest molecules show unusual physical properties, hence are promising for several kinds of advanced materials. Moreover, the unprecedented achievement of polymeric nanoporous crystalline phases (8 and e) has given very interesting results in the fields of molecular separations, water/ air purification and sensorics. 

When Cd(CN)2 is crystallized in the presence of other molecules that can stuff cavities or tunnels, many different structures are formed depending on the size and shape of the guests that stuff the cavities. Similar behavior is, of course, found elsewhere, e.g., in gas hydrates and hydrothermal synthesis of zeolites. These cadmium cyanide structures may be considered as a new class of clathrates. 

Solid hydrate research covers various classes of chemical compounds, which possess different importance and practical use. There are stoichiometric hydrates and those with varying water content as zeolitic hydrates. There are true hydrates and pseudohy-drates The latter contain water as hydroxide or hydroxonium ions or as -OH and -H groups ( water of constitution ). The true hydrates with separable H2O molecules ( water of crystallization ) include inorganic salts, i.e., the so-called salt hydrates, hydrates of organic compounds, and the clathrates, as, e.g., the novel gas clathrates. This article is mainly concerned with the salt hydrates. 

Clathrate hydrates (known also as gas hydrates) belong to a large class of crystalline, non-stoichiometric, inclusion-compound materials that are stable within a certain range of pressure and temperature. The host solid framework structure is made up of water molecules, connected through hydrogen bonds that form cavities (cages) . The cavities can be stabilized by the inclusion of small molecules such as CH4, CaHg, CO2, N2, Ar, etc. Over 100 different molecules are known to form hydrates. 

Petraccone V, Esposito G, Tarallo O, Caporaso L (2005) A New Clathrate Class of Syndiotactic Poly(p-methylstyrene) with a Different Chain Conformation. Macromolecules 38 5668-5674... 

Petraccone, V., Esposito, G, TaraUo, O., Caporaso, L. A new clathrate class of syndiotactic poly (p-methylstyrene) with a different chain conformation. Macromolecules, 38, 5668-5674 (2005). 

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