With metal halides from nonaqueous solvents

Intercalation from solutions in nonaqueous solvents (S21). This method may suffer from the drawback that final stoichiometries may not correspond to equilibrium conditions, because of partial leaching out of metal halide. For this reason, some chlorides can be intercalated only from solvents in which they have limited solubility iLS). It has often been the practice to wash intercalates with solvents to remove the excess of intercalant this may lead to stoichiometries lower than the original ones. The two-ampoule method may, therefore, be preferable (H24). 

From Mann s review, it is clear that the anion and the electrode material have a pronounced effect on the oxidation potentials of the nonaqueous systems. The metals to which the highest potentials can be applied in nonaqueous systems are obviously the noble metals (Pt, Au). The limiting reaction when the anions are halides (Cl-, Br, I ) was found to be their oxidation to the elemental form. When the anion is C104 , its oxidation onset at potentials above 1.5 versus Ag/ Ag+ may promote further intensive solvent degradation, as was found with ACN. It is important to note that using BF4 instead of C104- in ACN (which is an important and useful nonaqueous solvent in electrochemistry) extended its anodic stability limit by 2 V. 

The entropies of transfer, Aj5 (I, W -> S), are shown in Table 4.4 and were adapted from the aforementioned compilations [41] and [42]. It should be noted that the former were obtained from several extra-thermodynamic assumptions that were acceptable but the latter invariably from the TPTB one. Therefore, there are some inconsistencies (within 10 J K mol" ) and the later values should be preferred. The entropies of transfer from water to nonaqueous solvents are negative for small ions and positive only for the largest, hydrophobic, ions Bu4N, Ph P Ph As, and BPh T It should be noted that for the alkali metal cations, the magnitudes of AjN" (I, W -> S) show a most negative value somewhere in the middle of the series, but for the tetraalkylammonium and halide ions, the values are monotonous with the ionic sizes. On the whole, the standard molar entropies of small ions, whether cations or anions and irrespective of the charge and sign, show a pronounced uniformity. 

This methodology enjoys the merits of other approaches and exhibits several additional advantages 1) it has proven applicable to a wide range of transition metal and main group oxides 2) the metal precursors studied so far are readily available, being either alkoxide or halide complexes 3) in many cases, syntheses can be run in alcoholic solvents in essentially nonhydrolytic conditions, which aids in controlling hydrolysis and condensation rates 4) the critical micelle concentrations required for polyethylene-oxide-polypropylene-oxide di- and triblock copolymers are usually much lower than the concentrations needed for ionic surfactants and 5) because of the neutral, nonaqueous conditions used in these preparations, control of pH is not required, and the surfactant can be removed from the mesostructured material by calcination or milder solvent extraction methods with nonpolar solvents. 

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