Lithium cation, hydrated

As an example, infrared spectroscopy has shown that the lowest stable hydration state for a Li-hectorite has a structure in which the lithium cation is partially keyed into the ditrigonal hole of the hectorite and has 3 water molecules coordinating the exposed part of the cation in a triangular arrangement (17), as proposed in the model of Mamy (J2.) The water molecules exhibit two kinds of motion a slow rotation of the whole hydration sphere about an axis through the triangle of the water molecules, and a faster rotation of each water molecule about its own C axis ( l8). A similar structure for adsorbed water at low water contents has been observed for Cu-hectorite, Ca-bentonite, and Ca-vermiculite (17). 

Diuretics, interaction with lithium, 36 65-66 Divalent cations hydration shell, 34 211 structure, 34 210-212... 

For anionic monolayers, the reversal of the tt-A isotherms can be explained in terms of a competition between the anionic head groups and the alkali metal cations for molecules of water. If a modified Stern-type model of the plane interface is assumed, this interface will be composed of distinct adsorption sites, with counterions (cations) of finite size that can adsorb on these sites if the standard free energies of adsorption are favorable. If the anionic head group is more polarizable than water, as with carboxylic acids or phosphates, the hydration shell of the cation is incompletely filled, and the order of cation sizes near the interface is K+ > Na+ > Li+. When the polarizability of the anionic group is less than that of water, as with the sulfates, the lithium cation becomes the most hydrated one, and the order of cation sizes becomes Li+ > Na+ > K+. 

In addition to the concentration of the electrolyte solution, another barely examined factor influencing the structure and size of the hydration shells of ions is temperature. Invest tions of spin-lattice relaxation rates of and Li nuclei in aqueous LiCl solution as a function of concentration and temperature indicate that heating may destroy the tetrahedral water structure with inserted lithium cations that exists at temperatures below 30°C and enable the ions to construct a surrounding octahedral with the coordination number of 6 at temperatures above 40°C [165]. However,... 

On the other hand, cesium, rubidium, and, to a lesser extent, potassium are known as water structure breakers they cause the water molecules to be very disordered around the central cation. These larger cations have a small tendency to coordinate water molecules in a hydration shell, so lithium cations interact strongly with the (inner)... 

In contrast to and Rb", lithium picrate crystallizes with torand 1 as a 2 2 complex containing three water molecules.The two torands are coaxially stacked and threaded by a hydrated dilithium chain H20-Li -H20-Li -H20. Each lithium cation binds unsyinmetri-cally to two of the six nitrogens in each torand, and two water molecules complete the tetrahedral Li" coordination sphere. No anion coordination is observed, and hydrogen... 

Would this reaction be exothermic or endothermic What should happen to the magnitude of the enthalpies of hydration as one moves from the lithium cation down the alkali metals Briefly explain your answers. 

Applying the Polarization Model to the Hydrated Lithium Cation... 

The energy of this tri-hydrated Lithium cation is found to be -3186.6 kcal/mol, resulting in a hydration energy for the di-hydrate of -18.n kcal/mol, compared to the experimental A value of -20.7 kcal/mol. 

It is not at all clear what meaning to ascrihe to a structure such as that just presented for the tri-hydrated Lithium cation. To my knowledge, there is no evidence, in any physical state, to indicate whether or not this structure is correct, or reasonable, or whatever. 

Figure 4. One of the two minimum-energy conformations found for the di-hydrated lithium cation...

Figure 6. A low-energy structure (possibly a minimum) found for the four-hydrated lithium cation. The symmetric structure is of higher energy than this one, although there is no guarantee that the reported structure is a global mini-...

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