Inclusion neutral molecules

It should be pointed out that one cannot expect quantitatively correct data from such calculations. Clearly, the complexes considered do not appropriately represent real solutions. Most of the results obtained could have been guessed equally well by chemical experience and intuition anyway we expect ions to be more strongly hydrated than neutral molecules. In the actual calculations, the method employed is known to overemphasize the expected effects. The merits of attempts like the ones mentioned axe therefore not to be found in the realization of quantitative results, but verify that our expectations are definitely reproducable in terms of quantum chemical data, and they demonstrate how such calculations could be made. There have also been attempts to describe reactions of solvated molecules by an MO theoretical treatment for the two reaction partners, with inclusion of the solvent by representing it as point dipoles. As a first step, Yamabe et al. 186> performed ab initio calculations on the complex NH3.HF, solvating each of the partners by just one point dipole. A study of MO s of the interacting complex with and without dipoles shows that the latter has a favorable effect on the proceeding of the reaction. 

Several inclusion complexes with cations, anions and neutral molecules are discussed in Chapter 7 and in other parts of this book. 

Complexes are also formed in certain instances between neutral molecules and macrocyclic receptors. Neutral molecules which form such complexes for the most part contain polar O—H, N—H or C—H bonds, and hydrogen bonding interactions are responsible for the solid state structural characteristics of these complexes. For many of these complexes, stoichiometries range considerably, from 1 1 to 1 6 host guest, and include a variety of odd ratios such as 3 2, 2 7, etc. Structural results for these complexes indicate them not to be of the inclusion type in a majority of cases. Thus, discussion in this subsection will be limited to a general overview. A more complete review of neutral molecule complexation can be obtained elsewhere.21... 

Bott, S. G., Coleman, A. W., Atwood, J. L., Inclusion of both cation and neutral molecule by a calixarene - structure of the para leu Inily11neihoxycalix[4]aiene sodium loluene I cation.././Irn. Chem. Soc. 1986, 108, 1709-1710. 

Many gases, such as Ar, Kr, Xe, N2, O2, CI2, CH4 and CO, can be crystallized with water to form ice-like clathrate hydrates. The basic structural components of these hydrates are the (H2O)20 pentagonal dodecahedron and other larger polyhedra bounded by five- and six-membered hydrogen-bonded rings, which can accommodate the small neutral molecules. The inclusion properties of water imply that such polyhedra are likely to be present in liquid water as its structural components. 

The zeolite family of silicate minerals provide an example of hydrate structures of the former type. We have already seen ( 11.31) that these are framework silicates in which (Si, A1)04 tetrahedra are linked together into a three-dimensional network by sharing all oxygen atoms. This network, however, is far more open than that in other types of framework silicate and can readily accommodate water molecules in its interstices, whereas in, say, the felspars inclusion of water is not possible. The trivial function of water in the zeolites is emphasized by the fact that it can be expelled from the crystal without destruction of the structure and can even be replaced by other neutral molecules, such as those of ammonia, carbon dioxide, iodine and alcohol. The relatively complexity of some of these molecules attests the large size of the cavities available to accommodate them. 

The purpose of this review is to assemble and assess currently available information about structural modification of urea/thiourea inclusion compounds. We concentrate here on the structural aspects of new inclusion compounds with urea/thiourea/selenourea-anion host lattices, most of which were prepared and structurally analyzed in our laboratory. The versatility of urea or thiourea as a key component in the construction of novel anionic host lattices is clearly demonstrated by occurrence of many new types of linkage modes. The results show that co-molecular aggregates of urea or thiourea with other neutral molecules or anionic moieties can be considered as fundamental building blocks for the constructions of various types of novel host lattices. Comments on structure-property relationship for these inclusion compounds are made wherever appropriate. 

The results of our studies on urea/thiourea/selenourea-anion inclusion compounds have demonstrated that the classical urea or thiourea hydrogen-bonded host lattice can be modified in interesting ways by the incorporation of various anionic moieties, with or without cocrystallized water or other uncharged molecules, and that novel host frameworks bearing different urea, thiourea, or selenourea/guest molar ratios are generated by variation in size of the hydrophobic, pseudo-spherical R4N guest species. The stoichiometric formulas of 46 inclusion compounds and their structural details are listed in Table 10. For convenient description of stoichiometric ratios, the letters u, a, and c are used to denote the urea/thiourea/se-lenourea molecule, the anion, and the cocrystallized neutral molecule, respectively. 

In summary, we have shown that novel anionic host lattices can be constructed from urea, thiourea, or selenourea molecules and various anions as building blocks, which readily adopt different topologies for the accommodation of tetraalkylam-monium ions of various sizes. By employing organic cations as templates and suitable counter anions as an ancillary host material, with or without neutral molecules such as H2O as a third component, the lattice engineering of new urea, thiourea, and selenourea inclusion compounds by self-assembly may be further explored. 

Inelastic Neutron Scattering, p. Ill Isostructurality of Inclusion Compounds, p. 767 The Lock and Key Principle, p. 809 Macrocycle Synthesis, p. 830 Molecular Wires, p. 925 Self-Assembling Capsules, p. 1231 Simultaneous Binding of Cations and Anions, p. 129i Simultaneous Binding of Cations and Neutral Molecules, p. 1295... 

Canceill, J. Cesario. M. Collet. A. Guilhem. J. Pascard. C. A new bis-cyclotribenzyl cavitand capable of selective inclusion of neutral molecules in solution. Crystal structure of its CH2CI2 cavitate. J. Chem. Soc.. Chem. Commun. 1985. 361-363. 

The DPM moiety is a convenient building block for the design of cyclophanes able to form inclusion complexes with neutral molecules. However, an entropic cost must be assumed due to the conformational flexibility of DPM and derivatives. The best way to reduce the conformational entropy is to stabilize the gable conforination by back substitution, just as carried out in the case of DPN. 

On the other hand, the so-called solid-state complexes of multiarmed podands (e.g., hexahosts) with neutral molecules are more likely to be classed with clathrates (crystal void inclusion compounds). ... 

Negatively charged solid-state framework materials may show inclusion behavior where both countercations and neutral molecules are included. The most obvious example is the zeolites and related materials, however, a discussion of the inclusion characteristics of these materials is beyond the scope of this article. A relatively new field where such inclusion behavior may be observed is based on coordination polymers. Most coordination polymers are cationic or neutral, however one exception is... 

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