Hydrated sodium cations

Nmr methods have unrivalled potential to explore interfaces, as this account has striven to show. We have been able to determine the mobility of hydrated sodium cations at the interface of the Ecca Gum BP montmorillonite, as 8.2 ns. We have been able to measure the translational mobility of water molecules at the interface, their diffusion coefficient is 1.6 10 15 m2.s. We have been able to determine also the rotational mobility of these water adsorbate molecules, it is associated to a reorientational correlation time of 1.6 ns. Furthermore, we could show the switch in preferred reorientation with the nature of the interlayer counterions, these water molecules at the interface tumbling about either the hydrogen bond to the anionic surface or around the electrostatic bond to the metallic cation they bear on their back. And we have been able to achieve the orientation of the Ecca Gum BP tactoids in the strong magnetic field of the nmr spectometer. 

Noteworthy is the fact that permeation of butane through the crystal increases in time (1-2 days), while after evacuation the permeation reduces to the initial value and again increases in time. This has been explained in terms of structural transitions occurring in NaX. Initially, partially hydrated sodium cations block pores while upon exposure to butane and gradual drying, sodium cations move from the diffusion pathways, resulting in 10 the original permeation value. 

Zeolites with the FAU structure type can be prepared by direct synthesis with Si/Al ratios over a much narrower range (from 1 to ca. 5). The higher values refer to syntheses that use the crown ether 15-erown-5 as an additive. In these cases the sodium complex of 15-crown-5 is included in the structure. The lower charge density of the included complex compared to hydrated sodium cations requires less framework charge for charge balancing. Zeolite Y with much higher Si/Al ratios, required for catalytic applications, must be prepared by post-synthetic treatment (Chapter 6). 

Many authors have described the TGA curve for Mt and OMt in detail [2, 19, 26, 29, 32]. Typical TGA and derivate curves for pristine Mt and OMts are shown in Figure 8.6 and Figure 8.7. In Mt the first weight loss, in the range 50 to 150°C, corresponds to moisture, while the second one is related to the dehydroxilation of the aluminosilicate that takes place in the range of 380 to 650°C. On the other hand, OMts show lower content of humidity than Mt. This is related to the replacement of hydrated sodium cations by the surfactant molecules. In addition, the final residue decreases as the content of surfactant increases. 

Microscopic sheets of amorphous silica have been prepared in the laboratory by either (/) hydrolysis of gaseous SiCl or SiF to form monosilicic acid [10193-36-9] (orthosihcic acid), Si(OH)4, with simultaneous polymerisation in water of the monosilicic acid that is formed (7) (2) freesing of colloidal silica or polysilicic acid (8—10) (J) hydrolysis of HSiCl in ether, followed by solvent evaporation (11) or (4) coagulation of silica in the presence of cationic surfactants (12). Amorphous silica fibers are prepared by drying thin films of sols or oxidising silicon monoxide (13). Hydrated amorphous silica differs in solubility from anhydrous or surface-hydrated amorphous sdica forms (1) in that the former is generally stable up to 60°C, and water is not lost by evaporation at room temperature. Hydrated sdica gel can be prepared by reaction of hydrated sodium siUcate crystals and anhydrous acid, followed by polymerisation of the monosilicic acid that is formed into a dense state (14). This process can result in a water content of approximately one molecule of H2O for each sdanol group present. 

Sodium aluminate, NaAl(OH)4, is used along with aluminum sulfate in water purification. When mixed with aluminate ions, the acidic hydrated Al3+ cation from the aluminum sulfate produces aluminum hydroxide ... 

Now that we have an idea of the composition of solutions of strong electrolytes, we can move on to consider what happens when we pour one solution into another. A solution of sodium chloride consists of hydrated Na+ cations and hydrated Cl- anions. Similarly, a solution of silver nitrate, AgN03, consists of hydrated Ag+ cations and hydrated NO, anions. When we mix these two aqueous solutions, we immediately get a white precipitate, a cloudy, finely divided solid deposit. Analysis shows that the precipitate is silver chloride, AgCl, an insoluble white solid (Fig. 1.6). The colorless solution remaining above the precipitate in our example contains hydrated Na+ cations and hydrated N03 anions. These ions remain in solution because sodium nitrate, NaNO is soluble in water. 

Results obtained by ES/MS confirm that the stability of calixarene/cation complexes depends upon the medium. The calixarene in solution presents a strong affinity for cesium, whereas in the gas phase, it displays a stronger affinity for sodium. Moreover, the stability of calixarene/Na+ complexation in a solvent phase is increased by the presence of water in the dilution system (up to 40% in acetonitrile), whereas other alkali complexes are destabilized by the presence of water. Finally, affinity for sodium, which is weak in the solution for calixarenes bearing benzo moieties, considerably increases in the gas phase. These results confirm the interpretation of the MD simulations in an aqueous phase, which lead the authors to conclude that cesium-over-sodium selectivity is governed by the hydration of the sodium cation in the complex, and by the higher hydrophobicity of the complexation site leading to an enhancement of selectivity for cesium over sodium 49... 

By decreasing the water content in the core (Wo < 15), a decrease in the hydrated electron concentration occurs. At low values (Wo < 6) all molecules of water interact very strongly with the micelle core and electrons are less attracted in the process of hydration. At Wo values lower than 5, no solvation of the electrons has been observed in reverse micelles. When Wo increases, the water in the center of the pool is partially attracted by the hydration process of electrons. The absorption spectra of hydrated electrons in the core of the micelle are shifted toward short wavelengths compared to bulk water, thus showing that the water in the pool is different from the bulk water. This could be due to the fact that the sodium cations are very active in interaction with electrons (Llor and Rigny, 1986 Pileni, 1989b Pileni et al., 1982 Wong et al., 1976). 

FIGURE 1.2 Structure of a hydrated sodium Llano vermiculite determined by X-ray diffraction [5]. The experimental structure amplitudes were assigned phases calculated on the basis of scattering by the atoms of the silicate layers only, and the resulting observed structure factors (Fo values) were used, in conjunction with the calculated structure factors (Fc values), to compute Fo-Fc projections of the electron densities onto the 010 and the 100 faces of the unit cell, shown in the parts (a) and (b), respectively. That the interlayer cations and water molecules are in octahedral coordination accords with these Fourier projections. (Reproduced with kind permission of the Clay Minerals Society, from Slade, P.G., Stone, P.A., and Radoslovich, E.W., Clays Clay Min., 33, 51, 1985.)... 

Sodium-23 MASNMR measurements have been used to examine the extent to which this method can be used to determine the cation distribution in hydrated and dehydrated Y-zeolites. Results have been obtained on Na-Y and series of partially exchanged (NH, Na)-Y, (Ca,Na)-Y and (La,Na)-Y zeolites which demonstrate that the sodium cations in the supercages can be distinguished from those in the smaller sodalite cages and hexagonal prisms. For the hydrated Y zeolites, spectral simulation with symmetric lines allows the cation distribution to be determined quantitatively. 

ZnX and CeX. With both metals, 4 catalysts with different amounts of sodium cations replaced were prepared. The isomerization of 1-butene was studied over each catalyst at a range of temperatures, using catalyst samples weighing 0.1 gram after dehydration. The data from the TG experiments were used to calculate the amounts of hydrated catalysts required to give this weight of anhydrous material. In most cases, the course of the reaction at a given temperature followed the reversible first order equation... 

Strongly hydrated monovalent cations such as sodium are readily dissociated from the conjugate bases of the acidie groups in humie structures. Consequently, the solvated anions repel each other to give the random-coil-type conformations described in the previous section. Soils where sodium ions or other strongly hydrated monovalent cations predominate as the exchangeable species lose their humic substances in drainage waters. When... 

The synthesis of [Rh2(OAc)4(H20)2] from RhCl3-3H20, HOAc and NaOAc first gives [Rh2Cl2(OAc)4]2, which has now been crystallised and found to have the expected paddle-wheel structure the cations of the hydrated sodium salt are co-ordinated to one Cl and one OAc oxygen on adjacent dimers and to two water molecules.152 [Rh2(02CCF3)4(thf)] exists as two isomers, one being polymeric with... 

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