Clathrate neutral

CIO2 dissolves exothermically in water and the dark-green solutions, containing up to 8g/l, decompose only very slowly in the dark. At low temperatures crystalline clathrate hydrates, C102.nH20, separate (n 6-10). Illumination of neutral aqueous solutions initiates rapid photodecomposition to a mixture of chloric and hydrochloric acids ... 

Reduction of a,/3-unsaturated to saturated ketones was further achieved by electrolysis in a neutral medium using copper or lead cathodes (yields 55-75%) [766], with lithium in propylamine (yields 40-65%) [876], with potassium-graphite clathrate CgK (yields 57-85%) [807], and with zinc in acetic acid (yield 87%) [688]. Reduction with amalgamated zinc in hydrochloric acid (Clemmensen reduction) usually reduces both functions [877]. 

For clarity and because of space limitations, we will consider only examples of complexes in which the guest interacts with the host from above (or/and below) the cavity, and the structure has been confirmed by X-ray analysis. These complexes serve as models for the interaction of neutral molecules which are nearly concave/ convex complementary in their. spatial interaction. Although complementary in shape, some guest molecules simply fill spatial voids in the host lattice. These clathrate-like structures will not be considered. 

Clathrate hydrates can be formed not only with neutral organic molecules but also with alkylammonium salts with small anionic counteranions [37] and with guests involving polymeric anions [38]. 

Receptor and substrate are terms describing the species involved in complex formation. Throughout the chapter the receptor will refer tp the macrocyclic ligand, the substrate to other interacting species. Substrates may be metal or molecular catibns, neutral molecules, or atomic or molecular anions. The terms receptor and substrate imply that the complex formed has the well-defined structural and chemical properties of a supermolecule, as in biological receptor-substrate associations. They exclude species formed only in the solid state (clathrates). They are also easily converted and understood in many languages. 

Ionic liquids are potentially Green solvents and offer interesting properties as designer solvents and can act as liquid clathrates, including neutral guest molecules. 

Analytes may be small neutral molecules, simple anions or cations, complex ions or molecules, non-stoichiometric compounds, polymers, both soluble and insoluble, or clathrates. The chemical forms of the alkali and alkaline earth metals are either simple cations or hydrated cations and do not exhibit great variability so, of the metals of biological interest, this chapter will restrict itself to the... 

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. 

An interdisciplinary approach should lead to their future prospects as building blocks of a variety of chemical structures. Thus, betaines 1 can be incorporated as a subunit(s) in host molecules and could confer unusual properties to the supramolecules, either cavitates or clathrates. Their capacity for specific physical behavior should also be considered together with their use as neutral ligands (azolate ligands without counterion) in forming metal complexes. Advances in the chemistry of betaines 1, to be of any real significance, must result from coordinate efforts directed toward supramolecular chemistry, advanced organic materials, and heteroarene coordination chemistry. 

Several cluster models have been tested to account for patterns of small clusters (p = 1 or 2 bar in Fig. 18). First, clathrate models have been examined. The most popular of these consists of a regular dodedecahedron with one H2O molecule at each of the 20 vertices and possibly one additional molecule at the center. In this model, HjO molecules form regular pentagons with a molecular angle HOH of 108°, which is intermediate between 104.5°, the value for the free molecule, and 109.5°, that for tetrahedral bonding in the diamond cubic structure. Such a clathrate model, stabilized by an additional proton, accounts well for mass spectrometry results, but is found to be far too symmetrical to account for the structure of neutral clusters. An amorphous model,derived from Polk s random dense packing, has been tested. This... 

Earlier electrochemical investigations had shown that reductions can proceed beyond the two-electron stage a recent example is the behavior of [S2Mo18062]4- which, like other molybdates, can be reduced by up to six electrons.141,427-430 Density functional theory calculations have been reported for Keggin anions treated as clathrates of X04 - in a neutral M12036 shell these provide satisfactory explanations for the relative stabilities of the a- and /3-structures (see Table 8) and for the first reduction steps of 2, 2, and 2 electrons.109,431 Several structure determinations of heteropoly blues have now been reported but, as expected, none can unambiguously locate the... 

We define a co-crystal as a crystal that contains two or more different molecular species. We focus here on those crystals involving neutral organic molecules connected by hydrogen bonds. Thus, we exclude clathrates and complexes containing ionic species, such as those studied by Olovsson and his coworkers [12]. 

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). ... 

The structure of liquid water was dealt with in detail in Sect. 1.1.2. Once a solute, whether an ion or a neutral solute and whether hydrophilic or hydrophobic, is placed in the water, it is reasonable to expect it to affect the structure around it. The effects may be limited to a hydration shell surrounding the solute that has a structure differing from that in pure water. For instance, around monatomic ions the water molecules in the hydration shell are oriented towards the ion in a more or less spherical symmetry. Around hydrophobic solutes cages of water molecules are formed, that may be icelike but also resemble the structure of clathrates or crystal hydrates. In many cases the effects of the presence of an ion are manifested also beyond the hydration shell or shells. 

The problem was more compUcated to determine the ective radii of the guest species, because it depends of how far the electrons extend. The data found in handbooks for alkali-metals gave three series of values the ionic, the covalent and the metallic radii. As expected from the previous remark that alkali-metals in clathrates were essentially neutral, the ionic and the metallic radii were considered as inappropriate. The covalent radii as determined by Pauling seamed more realistic and, actually, proved to be consistent with experimental results, as shown in Fig. 1.4. The recently revisited values of covalent radii are about the same as the previous ones [39]. 

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