Alkali+-cationized molecules

For SiC>2, we have only considered sources for silica suspensions which were non-porous, such as Ludox (39), pyrogenic silica (40), heat-treated BDH silica (22), or ground quartz (41). The data from these sources at 0.1M concentration has been collected in Figure 7. The data of the various researchers is quite consistent, in spite of the differences in origin of the suspensions, and the different electrolytes used. The slope of the points above pH 7 shows that the adsorption capacitance for cations is very large for both sodium and potassium ions, around 200 pF/cm2. Such a capacitance corresponds to a distance of 0.25.X, when using the dielectric constant of immobilized water molecules. The equilibrium constant for adsorption is low, however, since both KNa+ and Kk+ lie between 0.1 and 0.01 dms/mol. A possible interpretation of these results is as follows there is little specific attraction between SiC>2 and alkali cations,... 

Easily ionizable anthracene forms the cation-radical as a result of sorption within Li-ZSM-5. In case of other alkali cations, anthracene was sorbed within M-ZSM-5 as an intact molecule without ionization (Marquis et al. 2005). Among the counterbalancing alkali cations, only Li+ can induce sufficient polarization energy to initiate spontaneous ionization during the anthracene sorption. The lithium cation has the smallest ion radius and its distance to the oxygen net is the shortest. The ejected electron appears to be delocalized in a restricted space around Li+ ion and Al and Si atoms in the zeolite framework. The anthracene cation-radical appears to be in proximity to the space where the electron is delocalized. This opens a possibility for the anthracene cation-radical to be stabilized by the electron s negative field. In other words, a special driving force for one-electron transfer is formed, in case of Li-ZSM-5. 

Both theory and experiment point to an almost perpendicular orientation of the two butadiene H2C=C(t-Bu) moieties (see Scheme 3.53). On passing from the neutral molecule to its anion-radical, this orthogonal orientation should flatten because the LUMO of 1,3-butadiene is bonding between C-2 and C-3. Therefore, C2-C3 bond should be considerably strengthened after the anion-radical formation. The anion-radical will acquire the cisoidal conformation. This conformation places two bulky tert-butyl substituents on one side of the molecule, so that the alkali metal counterion (M+) can approach the anion-radical from the other side. In this case, the cation will detain spin density in the localized part of the molecular skeleton. A direct transfer of the spin population from the SOMO of the anion-radical into the alkali cation has been proven (Gerson et al. 1998). 

Metal hexacyanoruthenates possess a lower symmetry. Several compounds have highly disordered structures, especially when no alkali cations are present for charge compensation. Such a complex defect structure has been found for a completely potassium free Prussian blue precipitated very slowly from a solution in concentrated hydrochloric acid [25, 26]. Here, the structure still remains cubic face-centered however, one-third of the [M1 -1(CN)6] is vacant, randomly distributed and that space is filled with water molecules. The coordination sphere of the remaining ions is maintained... 

A plethora of crown ether- or cryptand type molecules have been reported. Some of them are depicted below to show their diversity and versatility. Lariat azaether containing cyclen macrocycle 208 [36] and azaethers involving triazole 209 [37], furane or pyrrole containing macrocycles which can complex two copper 210 [38] or one barium cations 211 [39], spiro-linked crown ethers 212 [40] andcagecompounds 213 [41] which, in addition to two alkali cations, could... 

Multisite crown ethers (30) and (31) are polymacrocycles. These molecules are potentially like cryptands in view of the possibilities for forming inclusion-like species. The photoresponsive crowns provide an excellent example of this aspect, and consist of two crown ethers, as in (30a and 30b), attached via a photosensitive azo linkage. This molecule undergoes reversible isomerization (likened to a butterfly motion), shown in equation (13). The cis form gives a stable 1 1 cation ligand complex with the larger alkali cations (actually a 1 2 cation crown ratio). Concentrations of (30b) in solutions are thus noted to be enhanced by the addition of these cations.100,101 Other multisite crowns have been prepared from diphenyl- and triphenyl-methane dyes, e.g. (31).102... 

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. 

Some interesting effects associated to the presence of well-defined structural units appear on a broad class of binary alloys formed by mixing an alkali metal (Li, Na, K, Rb, Cs) with a tetravalent metal like Sn or Pb. Due to the large difference in electronegativities it is normally assumed that one electron is transferred from the alkali to the tetravalent atom. As the Sn- or Pb-anions are isoelectronic with the P and As atoms, which in the gas phase form tetrahedral molecules P4 and AS4, in the same way the anions group in the crystal compounds forming (Sn4)4- and (Pb4)4- tetrahedra, separated by the alkali cations. This building principle was developed by Zintl in the early thirties [1], and the presence of such tetrahedra has been detected in the equiatomic solid compounds of Pb and Sn with Na, K, Rb and Cs, but not with Li [2, 3, 4]. In this paper we focus on alkali-lead alloys. 

Electronic Structure and Spectra of Light Alkali Diatomic Molecules and Their Molecular Cations... 

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