Lithium solvation

TABLE 1. Relative lithium solvation strengths (A soiv) for different solvents determined for the equilibrium in Scheme 6... 

Only two structural studies have been reported for lithium solvates in non-aqueous solutions. In an XD study of concentrated formamide solution of LiCl [36] the lithium ion was found to be solvated by 5.4 formamide molecules in average and the Li-O distance was reported to be 2.24A, in keeping with the values found in diluted aqueous solutions. More recently, a detailed study has been performed by combination of the ND method with a series of theoretical methods on an 0.6 mol dm LiBr solution in acetonitrile [37]. The lithium ion was found to be tetrahedrally coordinated by three solvent molecules and one bromide ion. The Li-N distance resulted in 2.05 A. 

From these data it is suspected that the molecules of the solvate structure of lithium ion might be largely effected by the solvent molecules. Since the solubility of some lithium salts is relatively high in MN-dimethyl formamide (DMF), concentrated solutions can also be examined. In a previous study the solvate structure of lithium has been described in an 1.5 mol dm LiNCS solution in DMF [38]. A new XD measurement has been carried out for a LiCl solution of the same concentration. Table 1 hows the structural parameters for the lithium solvates in both solutions. The structural parameters were determined by a least-squares fitting method (LSQ). After the subtraction of the contributions ascribed to the intramolecular stmcture of the DMF molecules and to the assumed structure around the anions from the total structure function of the solution, the resulted difference curve was approximated by calculated model curves. The result is shown in Figure 1. 

As pointed out by Langer (and verified by Hay, Antkowiak, and Uraneck), both chelate type and temperature effects indicate that specific lithium solvation rather than a general solvent effect are operable here. Also, this high degree of lithium solvation results in propagation from a truly anionic reacting site located mainly at the secondary carbon of the terminal, active, delocalized allyl carbanion in the growing polymer. 

Endres, R Borisenko, N. El Abedin, S.Z. Hayes, R. Addn, R., The interface ionic liquid(s)/ electrode(s) In situ STM and AFM measurements, Faraday Dsicuss., 2012,154, 221-233. Lassfegues, J.-C. Grondin, J. Talaga, D., Lithium solvation in bis(trifluoromethanesulfonyl) imide-based ionic liquids, Phys. Chem. Chem. Phys., 2006, 8,5629-5632. 

The initiation step is very important in the production of liquid HRs by ionic methods. To obtain reproducible results, the initiator should be soluble in the butadiene solution. Solubility is easily obtained in the ethers commonly used as lithium solvating agents. To obtain the best mechanical properties and heat aging characteristics, it is desirable that 1,2-addition be kept to a minimum. It has therefore become customary to prepare initiator in an ether, dilute it with a hydrocarbon solvent, and then distill off as much of the ether as possible [303]. 

A more recent study of ethynyllithium included the effect of lithium solvation on dimerization. At the 6-3H-G level successive coordinations of water to form HCCLi(OH2), HCCLi(OH2)2, and HCCLi(OH2)3 have AE of —21, —10, and —5 kcal mol , respectively. As solvation of lithium increases, the dimerization to the corresponding solvated ethynyllithium dimer becomes less exothermic. An interesting further feature is that the dimer with two waters per lithium has D2, symmetry, with each tetracoordinated carbon associated with two terminal ethynyl carbons and two waters. With fewer waters of solvation the coordination number of the lithiums is increased by association with the r-bond of the acetylene. This feature... 

Lassegues J-C, Grondin J, Talaga D (2006) Lithium solvation in bis (trifluorometheuiesulfonyl) imide-based ionic liquids. Phys Chem Chem Phys 8 5629-5632... 

Ionic polymers may exist as undissociated, unsolvated ion pairs undissociated ion pairs solvated to some extent solvated ions dissociated to some extent or some combination of these. The propagation rate constant kp and the dissociation equilibrium constant K of the lithium salt of anionic... 

The physical picture in concentrated electrolytes is more apdy described by the theory of ionic association (18,19). It was pointed out that as the solutions become more concentrated, the opportunity to form ion pairs held by electrostatic attraction increases (18). This tendency increases for ions with smaller ionic radius and in the lower dielectric constant solvents used for lithium batteries. A significant amount of ion-pairing and triple-ion formation exists in the high concentration electrolytes used in batteries. The ions are solvated, causing solvent molecules to be highly oriented and polarized. In concentrated solutions the ions are close together and the attraction between them increases ion-pairing of the electrolyte. Solvation can tie up a considerable amount of solvent and increase the viscosity of concentrated solutions. 

The THF solvate of lithium i-butylacetylide is another example of a tetrameric structure. ... 

Fig. 7.3. Crystal structures of some lithium etiolates of ketones. (A) Unsolvated hexameric enolate of methyl t-butyl ketone (B) tetrahydrofuran solvate of tetramer of enolate of methyl r-butyl ketone (C) tetrahydrofuran solvate of tetramer of enolate of cyclopentanone (D) dimeric enolate of 3,3-dimethyl-4-(r-butyldimethylsiloxy)-2-pentanone. (Structural diagrams are reproduced from Refs. 66-69.) by permission of the American Chemical Society and Verlag Helvetica Chimica Acta AG.

Scheme 10.10 and if Coordination modes for the [RSNR ] anion in solvated lithium complexes... 

Aminoborolide dianion [C4H4BN(i-Pr)2] taken as the THE solvate of a lithium salt with Cp MCl3 (M = Zr, Hf) in ether gives 294 (94JA4489). The nitrogen atom... 

Additives Modifying the State of Solvation of Lithium Ions... 

Whereas the electrochemical decomposition of propylene carbonate (PC) on graphite electrodes at potentials between 1 and 0.8 V vs. Li/Li was already reported in 1970 [140], it took about four years to find out that this reaction is accompanied by a partially reversible electrochemical intercalation of solvated lithium ions, Li (solv)y, into the graphite host [64], In general, the intercalation of Li (and other alkali-metal) ions from electrolytes with organic donor solvents into fairly crystalline graphitic carbons quite often yields solvated (ternary) lithiated graphites, Li r(solv)yC 1 (Fig. 8) [7,24,26,65,66,141-146],... 

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