Lithium stoichiometry

The solid circles in Figure 5.13a-e denote the initial current levels Jin, at various potential steps A , calculated from the corresponding CTs. Invariably, all of the li i versus A plots show a linear relationship. It should be mentioned that even diffusion-controlled CTs can exhibit this type of linear relationship, in the case that the electrode potential curves vary linearly with lithium stoichiometry, A oc ( -c ). However, the linear relationship between and A is still valid for the electrodes (e.g., Lii + 5[Ti5/3Lii/3[O4, Lii 5CoO2, LisV2O5 and graphite) where the electrode potential versus lithium stoichiometry curves deviate strongly from the linear relationship. 

The titration consists of addition of a few milliliters of distilled water and an excess of standard HCl (0.1 N), followed by back-titration with standard NaOH solution (0.1 N). The lithium stoichiometry is calculated on the basis of the titration results. It has been shown that this total base titration gives the same results as are obtained with active lithium reagent and atomic absorption analysis. 

Complete lithiation to the limiting lithium stoichiometry of Li2.oRe03 may require more than one n-BuLi treatment. This can be due in part to dilution of n-BuLi as the reaction proceeds. Upon titrating the initial /i-BuLi reaction solution, 10.491 mmol of Li remains from an original 3.059 N n-BuLi solution containing 12.5 mL (38.238 mmol) of n-BuLi in hexane and 4.080 g (17.421 mmol) of ReOj. This indicates 1.59 mmol of Li per millimole of ReOj. Further lithiation and subsequent titration results in Lia.jReOj. X-ray powder diffraction data indicates the lithium composition, in excess of two Li per ReOj, is due to impurities in the ReO,. 

Confirmation of the lithium stoichiometry is determined by an iodine reaction that yields the amount of lithium removed from the structure. A titration (described in Section A) performed after reaction of Li JleOj with a standard iodine solution affords the stoichiometry Li, ReOj. 

Reaction of 4.189 g of LijReO, together with excess absolute ethanol (—55.0 mL total) forms 19.45 mmol of lithium ethoxide. Therefore, 1.0 mmol of Li is removed from the structure, leaving Li, oReO,. Removal of all of the lithium using the standard iodine solution technique confirms the lithium stoichiometry. 

MPD-1 fibers may be obtained by the polymeriza tion of isophthaloyl chloride and y -phenylenediamine in dimethyl acetamide with 5% lithium chloride. The reactants must be very carefully dried since the presence of water would upset the stoichiometry and lead to low molecular weight products. Temperatures in the range of 0 to —40° C are desirable to avoid such side reactions as transamidation by the amide solvent and acylation of y -phenylenediamine by the amide solvent. Both reactions would lead to an imbalance in the stoichiometry and result in forming low molecular weight polymer. Fibers are dry spun direcdy from solution. 

The stoichiometry (4 mol lithium hydride to 1 mol LiAlH ) makes this an inherently expensive process, even though high yields of pure product are obtained. For large-scale production, metathesis from NaAlH is economically preferred. 

Compounds of the same stoichiometry type usually have the same type crystal structure within the row of alkali metals K - Rb - Cs rarely the same type structure with sodium-containing analogues and never ciystallize similarly with lithium-containing compounds. The crystal structure analysis of different fluoride and oxyfluoride compounds clearly indicates that the steric similarity between all cations and tantalum or niobium must be taken into account when calculating the X Me ratio. 

In comparison with graphite, non-graphitic carbons can provide additional sites for lithium accommodation. As a result, they show a higher capability of reversible lithium storage than graphites, i.e., stoichiometries of x> in Li C6 are possible. 

It is intriguing to note that this reaction scheme for the reduction of a sulphone to a sulphide leads to the same reaction stoichiometry as proposed originally by Bordwell in 1951. Which of the three reaction pathways predominates will depend on the relative activation barriers for each process in any given molecule. All are known. Process (1) is preferred in somewhat strained cyclic sulphones (equations 22 and 24), process (2) occurs in the strained naphtho[l, 8-hc]thiete 1,1-dioxide, 2, cleavage of which leads to a reasonably stabilized aryl carbanion (equation 29) and process (3) occurs in unstrained sulphones, as outlined in equations (26) to (28). Examples of other nucleophiles attacking strained sulphones are in fact known. For instance, the very strained sulphone, 2, is cleaved by hydride from LAH, by methyllithium in ether at 20°, by sodium hydroxide in refluxing aqueous dioxane, and by lithium anilide in ether/THF at room temperature. In each case, the product resulted from a nucleophilic attack at the sulphonyl sulphur atom. Other examples of this process include the attack of hydroxide ion on highly strained thiirene S, S-dioxides , and an attack on norbornadienyl sulphone by methyllithium in ice-cold THF . ... 

The specific capacity obtained in such Ams, actually corresponds to near theoretical limit of 372 mA-h/g, as calculated on a basis of classical LiC6 stoichiometry). Further increase of capacity is possible only via switching to new or modified materials, composites or alloys, which are capable for reversible and stable intercalation of lithium. 

Monomeric carbene complexes with 1 1 stoichiometry have now been isolated from the reaction of 4 (R = Bu, adamantyl or 2,4,6-trimethylphenyl R = H) with lithium l,2,4-tris(trimethylsilyl)cyclo-pentadienide (72). The crystal structure of one such complex (R = Bu) revealed that there is a single cr-interaction between the lithium and the carbene center (Li-C(carbene) 1.90 A) with the cyclopentadienyl ring coordinated in an if-fashion to the lithium center. A novel hyper-valent antimonide complex has also been reported (73). Thus, the nucleophilic addition of 4 (R = Mes R = Cl) to Sb(CF3)3 resulted in the isolation of the 1 1 complex with a pseudo-trigonal bipyramidal geometry at the antimony center. 

A convenient route to andiides, where Li and A1 centers are, at the same time, involved is represented by the reaction of LiAlH4 with primary silylphosphanes and silylarsanes (Scheme 4) (67). However, the outcome of such reactions is dependent on the stoichiometry. The silylarsane 2c reacts with LiAlH4 in the molar ratio of 4 1 in 1,2-dimethoxyethane, under evolution of H2, resulting in the corresponding tetrakis(arsaneyl)-substituted lithium alanate 36c in quantitative yield. The similar transformation of the arsane 2a with LiAlH4 in the... 

For example, atoms of both the alkaline-earth family (ZAval = 2) and the chalcogen family (ZAval = 6) correspond to FAemp = 2, and their stoichiometric proportionality (or coordination number) to monovalent atoms is therefore commonly two (AH2, ALi2, AF2, etc.). It is a remarkable and characteristic feature of chemical periodicity that the empirical valency FAemp applies both to covalent and to ionic limits of bonding, so that, e.g., the monovalency of lithium (Vuemp = 1) correctly predicts the stoichiometry and coordination number of covalent (e.g., Li2), polar covalent (e.g., LiH), and extreme ionic (e.g., LiF) molecules. Following Musher,132 we can therefore describe hypervalency as referring to cases in which the apparent valency FA exceeds the normal empirical valency (3.184),... 

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