Cavity pseudo

Most of the chalcogenide studies have involved binary, ternary, and pseudo ternary metal clusters. The ternary Chevrel-phases can be represented by MxMo6X8 (M = transition metal, X = chalcogen atom), where the transition metal fills the cavities in the Mo6X8 crystal structure. The pseudo-ternary (or pseudo-binary) Chevrel-phase clusters can be represented by MxMo6 xX8, where the Mo atoms are substituted by transition metal atoms.185 The crystal structure of ternary and pseudo ternary Chevrel phases are shown in Fig. 4. The carbonyl-chalcogenide clusters189 192 will be discussed in the next section. 

For the metabolism rangefinding experiments, sea urchins were dosed by injection at a level of 2.2 mg/kg of body weight with -PNA into the central cavity, held in untreated water at 12°C, and both the water and coelomic fluid sampled periodically over the course of 8 hours. Most of the PNA was eliminated rapidly into the water (Fig. 2), with a pseudo-first order half-life of appearance of 12 minutes half of the test compound was lost from the coelomic fluid in about 24 minutes. 

The solid state structure determination of 12d undoubtedly proved the iiii configuration of the molecule, which presents a pseudo-C4 symmetry with the P=0 bonds directed inward (Fig. 1) [66]. The crystal contains six solvent molecules per host. One acetonitrile molecule was found as a guest in the aromatic cavity. At the lower rim, a second molecule of acetonitrile occupied the position between the four long chain substituents. 

TCO4 analogue to be almost perfectly situated with its three oxygen atoms down into the cavity and more or less in line with the pseudo threefold axis (Figure 19). 

Discrete dimers of the head-to-head type have been found in the structures of the Ag+ complex of (145)570 and the Na+ complex of (145)571 respectively. The complexes were recrystallized from carbon tetrachloride. In both complexes each metal is five-coordinated in the cavity provided by one anion, and there is an additional reaction with the second anion [through an Ag+-phenyl interaction or an Na+-carboxylate oxygen atom (Figure 32a)]. When the Na+ complex was crystallized from a solvent of medium polarity, acetone, the head-to-head dimer was recovered.571 In contrast, recrystallization from a polar medium, methanol, gave a monomeric complex in which one methanol of solvation was also present.572 In all of these complexes an intramolecular head-to-tail hydrogen bond was present to hold the ligand in its pseudo-macrocyclic conformation. 

In a subsequent report, in 2005 [55], the same group described the preparation of imprinted polymer capable of oxidising alcohols and alkanes with 2,6-dichlor-opyridine /V-oxide (86) without mineral acid activation. The polymer was imprinted with a ruthenium porphyrin complex (87) using the diphenylmethana-mine (88) as pseudo-substrate template in order to achieve a shape of the cavity complementary to the substrates, diphenylmethane (89) and diphenylmethanol (84). The reaction, carried out with the imprinted polymer on the diphenylmethanol as substrate, showed a rate enhancement 2.5 higher than with the non-imprinted polymer. In the same conditions, but with diphenylmethane and... 

The X-ray structure of the L-Sr(Picrate)2 (L = p-tert-butyl-calix[4]arene-tetra(diethylamide)) is reported, as well as MD simulations on the L M2+ complexes in vacuo, in water, and in acetonitrile solutions for alkaline earth cations with a comparison of converging and diverging conformers.130 In the simulated and solid-state structures of the L M2+ complex, the ligand wraps around the complexed cations M2+ (more than it does with alkaline cations), which are completely encapsulated within the polar pseudo-cavity of L, without coordination to its counterion in the crystal or to solvent molecules in solution. In contrast to alkali cation complexes, which display conformational flexibility in solution, computations show that the alkaline earth cation complexes are of the converging type in water and in acetonitrile. Subtle structural changes from Mg2+ to Ba2+ are observed in the gas phase and in solution. Based on FBP calculations, a binding sequence of alkaline earth cations was determined Mg2+ displays the weakest affinity for L, while Ca2+ and Sr2+ are the most stable complexes, which is in agreement with the experiment. 

A pseudo potential approach was adopted by Hickman et al. [259] to calculate the excited metastable states of a He atom under liquid He. The density functional approach developed by Dupont-Roc et al. [260] was applied subsequently [261] for the description of the nature of the cavity formed around an alkali atom in the excited state of non-zero angular momentum. The resulting form of the cavity differs very much from the spherical shape. A similar approach was adopted by De Toffol et al. [262] to find qualitatively the first excited states of Na and Cs in liquid He. Earlier work in this direction was given in detail in Ref. [263]. 

In the smaller cryptand, 5, with the w-xylvl spacers, the structure of crystals obtained from the reaction of the cryptand with HF indicated a single fluoride in the cavity with a water molecule companion (Figure 9) [31,33], The structure contained two bifluorides, but outside the cavity, in addition to seven waters and 1.5 SiF62 ions. The internal fluoride is pseudo-tetrahedrally hydrogen bonded to the internal molecule... 

Structure determinations of salts containing [R c P5W30O110]12-, R = Y, Eu, and a redetermination of the sodium derivative, showed that the central cavity also contained a water molecule coordinated to the encrypted cation (Dickman et al., 1996 Kim et al., 1999). This observation, also noted for the Ca and structures, provides an explanation for the fact that the encrypted cation does not lie in the pseudo-equatorial mirror plane of the polytungstate framework. Luminescence lifetime measurements on the europium complex have led to ambiguous conclusions regarding the number of coordinated water molecules (Soderholm et al., 1995 Lis et al., 1996). As shown in Table 9 the 31P chemical shifts are significantly affected by the acidity of the solution. Remarkably, at intermediate acidities... 

Myoglobin contains Fe2+ (d6 configuration) in a high-spin state, which has a radius of about 78 pm in a pseudo-octahedral environment. The Fe2+ ion is too large to fit into the central cavity of the porphyrin ring, and lies some 42 pm above the plane of the N donor atoms. When a dioxygen molecule binds to Fe2+, the Fe2+ becomes low-spin d6 with a shrunken radius of only 61 pm, which enables it to slip into the porphyrin cavity. 

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