Ion insertion

Members of the ion-insertion/extraction group, as inorganic or organic thin films, especially the former, have attracted the widest interest most recently. Tungsten trioxide was the eadiest exploited inorganic compound (4), even before the mechanism of its electrochromic response was understood (5). It is stiU the best known of the important ion-insertion/extraction group. 

The seminal work on these materials began at American Cyanamid Co. in the 1960s (4,23), though these workers did not author the ion-insertion/extraction model that has become widely accepted (5). Numerous patents were granted to American Cyanamid Co. as a result of its display-oriented work. Much of what others have written in the open Hterature either confirms or adds to what these teach. Important papers (16) about... 

The same color variety is not typical with inorganic insertion/extraction materials blue is a common transmitted color. However, rare-earth diphthalocyanine complexes have been discussed, and these exhibit a wide variety of colors as a function of potential (73—75). Lutetium diphthalocyanine [12369-74-3] has been studied the most. It is an ion-insertion/extraction material that does not fit into any one of the groups herein but has been classed with the organics in reviews. Films of this complex, and also erbium diphthalocyanine [11060-87-0] have been prepared successfiiUy by vacuum sublimation and even embodied in soHd-state cells (76,77). 

The reactions of these insertion materials, except for LiMnO, [19, 20], consist of electron and lithium-ion insertion into, or extraction from, each matrix without the destruction of its core structure this is called a topotactic reaction. A series of LiCovNi, v02 (0 < y < 1)) and... 

Table 2. Commercially available rechargeable coin-type cells with lithium-ion inserted anodes...

An Alternative to the Lithium-Metal Anode (Lithium-Ion Inserted Anodes)... 

Recently, lithium-ion inserted compounds have been investigated as new anodes. These compounds have the possibility of... 

Rare-earth ions inserted in the tetraborides have the 34- oxidation state, except for CeB4 and YbB4 (see Fig. 2). The abnormal volume contraction for the CeB4 unit cell can be explained by the presence of some Ce ions . Recoilless y-ray emission spectra and magnetic measurements indicate that ytterbium in YbB4 has an intermediate valence state as in YbAl3... 

The thermodynamic properties of magnesium make it a natural choice for use as an anode material in rechargeable batteries, as it may provide a considerably higher energy density than the commonly used lead-acid and nickel-cadmium systems, while in contrast to Pb and Cd, magnesium is inexpensive, environmentally friendly, and safe to handle. However, the development of Mg-ion batteries has so far been limited by the kinetics of Mg " " diffusion and the lack of suitable electrolytes. Actually, in spite of an expected general similarity between the processes of Li and Mg ion insertion into inorganic host materials, most of the compounds that exhibit fast and reversible Li ion insertion perform very poorly in Mg " ions. Hence, there... 

As discussed in Chapter 2, there are a number of important iron-containing enzymes which have neither haem nor Fe-S clusters. While we assume that they get their iron from the LIP, it is not yet established whether or not there are specific enzyme systems involved in the metal-ion insertion. 

The kinetics and mechanism of metal ion insertion into porphyrins has been the subject of a considerable number of studies. As expected, relative to the formation of complexes of flexible macrocycles, such reactions are slow. For the overall reaction M2+ + LH2 ML + 2H+... 

The need for multiple desolvation of the metal ion in some systems may provide a barrier to complex formation which is reflected by lower formation rates - especially for inflexible macrocycles such as the porphyrins. Because of the high energies involved, multiple desolvation will be unlikely to occur before metal-ion insertion occurs rather, for flexible ligands, solvent loss will follow a stepwise pattern reflecting the successive binding of the donor atoms. However, because of the additional constraints in cyclic systems (relative to open-chain ones), there may be no alternative to simultaneous (multiple) desolvation during the coordination process. 

Fig. 9.15 Schematic models for ion insertion during redox processes of polymer electrodes electropolymerised in the presence of small (case ( )) and large (case (h)) anions. A = electrolyte anion = electrolyte cation L" = large anion.

Thermolysis of the thiadiazole (164) leads to elimination of isocyanate and sulfur giving the triazine derivative (167). If the thermolysis is carried out in the presence of phenols 2-aryl-benzimidazoles (168) are produced <85JCS(P1)1007>. The S—N bond of (157) is readily cleaved with both N- and C-nucleophiles. Thus, treatment of (157) with an excess of amine gives the sulfenamide (169) (Scheme 39) and reaction of (157) with active methylene compounds leads to derivatives of type (170) (Scheme 39) which on heating furnish (171). Cyanide ion inserts into the S—N bond of (164), probably via the intermediate (172) which immediately recyclizes to give the thiadiazinone (173) (Scheme 40) <85JCS(P1)1007>. 

Wang D, Choi D, Li J et al (2009) Self-assembled Ti02-graphene hybrid nanostructures for enhanced Li-ion insertion. ACS Nano 3 907-914... 

Such electrochemical processes can be described on the basis of the model developed by Lovric and Scholz [115, 116] and Oldham [117] for the redox reactivity of nonconducting solids able to be permeated by cations or anions (so-called ion-insertion solids). As described in the most recent version of Schroder et al. [118], the electrochemical process is initiated at the three-phase junction between the electrode, the electrolyte solution, and the solid particle, as schematized in Fig. 2.6. From this point, the reaction expands via charge diffusion across the solid particle. It is assumed that, for a reduction process, there is a flux of electrons through the... 

The use of these methods for speciation in solid materials requires that two essential assumptions—electrochemical reversibility and diffusive control—apply. Under these circumstances, theoretical CVs for ion-insertion solids are essentially identical to those for speeies in solution [206]. Since solid-state processes involve coupled... 

In the nonstochiometric redox state, intervalence charge transfer between adjacent WVI and Wv sites leads to the observed intense blue color. Apparently, if the ratio of WVI to Wv is increased further, the ion insertion becomes irreversible, resulting in a permanent color change to red or golden [34,35]. It should be noted that in spite of the apparent progress in explaining the electrochromism on a fundamental level, questions remain and alternate mechanisms have been proposed which suggest the involvement of other oxidation states [36]. 

The structures of the hydrides, oxides and nitrides in this group are rather peculiar, for they can always be described as lattices, as found in pure metals, with the negative ions inserted in the octahedral holes of these structures. In the case of TiN, TiO and, in general, all compounds AB, all octahedral holes are occupied, and the structure is that of the sodium chloride type. There are nitrides of other types, too, e.g. A2N, A3N, etc., in which cases only a part of the octahedral holes are occupied. 

The possible factors involved in the biological selectivity towards metal ions have been considered by Frausto da Silva and Williams3 and by Kustin et al.4 In terms of thermodynamic selectivity a useful formalism for the uptake of any metal ion from a multimetal system is the quotient A Cm, where Km is a relative stability constant and Cm is the concentration of the metal ion. However, as these authors point out,3 a combination of both thermodynamic and kinetic properties must be considered. An appreciation of kinetic factors is often absent in this field, but must be of prime consideration in chelate exchange reactions and in the final irreversible step of metal ion insertion to form the metalloenzymes. 

Chu, Y.Q. and Q.Z. Qin. 2002. Fabrication and characterization of silver-V205 composite thin films as lithium-ion insertion materials. Chem. Mater. 14 3152-3157. 

Hydrogen-bonded supramolecular capsule I compared with coordination capsule II. The external aliphatic groups are omitted for clarity. Note that a pair of intermolecular O—H O hydrogen bonds is replaced by four square-planar Cu-O coordination bonds in the metal-ion insertion process that generates the isostructural inorganic analog. From R. M. McKinley, G V. C. Cave and J. L. Atwood, Proc. Nat. Acad. Sci. 102, 5944-8 (2005). 

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