Metal ions pairing

After an extensive review of MMCT transitions involving ions in solids, it seems wise to start this paragraph with some molecular species, because many of these have been investigated in much more detail than their counterparts in non-molecular solids. It is suitable to make a distinction between outer-sphere charge-transfer (OSCT) and inner-sphere charge-transfer (ISCT) transitions [1], In the former the metal ions do not have ligands in common, in the latter they are connected by a common ligand. Studies are usually performed on metal-ion pairs in solution. 

Use tape or a permanent marker to label the outside of nine wells of your egg carton with the nine different half-cells. Each well should correspond to one of the eight different metal/metal ion pairs Mg/Mg ", Cu/Cu, A1/AP+, Ni/Ni h Zn/Zn2+, Sn/Sn2+, Fe/Fe, and Ag/Ag. Label the ninth well H /H2. 

In the case of alkali metals, ion pairing can be visualized as HFCs from paramagnetic nuclei of the metal cations associated with organic anion-radicals in ethereal solvents. In this respect, an alkali metal cation associated with the anion-radical of o-dimesitoylbenzene in DME or THF serves as a paradigm (Herold et al. 1965). 

TABLE 1. Effect of metal ion pairing on the apparent experimental pkTa value of diethylmalonate (24). Reprinted with permission from Reference 233. Copyright 1980 American Chemical Society... 

The photochemical activation of the phosphonium salt (Eq. 55) has its thermal counterpart in the facile (dark) conversion of the iodonium salt Ph2l+ Mn(CO)s . Owing to the greatly enhanced reduction potential of diphenyliodonium (Ered 0 V relative to the SCE [181]) as compared to tetraphenylphosphonium (Ered 2.3 V relative to the SCE [140]), electron transfer in the iodonium-metallate ion pair is now energetically feasible (AGet 0 eV). As a result, complete conversion of the charge-transfer salt to the electron-transfer products Mn2(CO)io and PhMn(CO)s is observed within minutes upon mixing of the two components [140]. 

Additional reagents useful for secondary equilibrium include borate buffer for carbohydrates, chelating agents for transition metals, ion-pair reagents for acids and bases, transition metals for proteins and peptides, silver ion for alkenes, and Mg for nucleosides. 

Electron-metal+ ion-pairs are more reactive than the free solvated electrons in reactions yielding alkoxide or amides. Apparently, the charge transfer required for the formation of those anions is facilitated by the proximity of Met+ cation which becomes coordinated with the oncomming X-OR reagent. Since, in contrast to liquid ammonia, ion-pairs are the abundant species in organic amine or ether solutions, these directly... 

In contrast, the three ligands 96 are designed for the simultaneous recognition of a 4f-3d metal ion pair (96a) (Piguet et al., 1996), a homopair of 4f ions (H296b) (Elhabiri et al., 1999), or a heteropair of 4f ions (96c) (Andre et al., 2002). For instance, under stoichiometric conditions, [M Ln (96a)3] is the only species formed out of a potential mixture of at least six species (three and two Ln -containing complexes were identified in solutions with... 

The preparation of the first one was based on discoveries of Dye and Edwards concerning the dissolution of alkali metals potassium or sodium in an aprotic solvent, such as THE, containing a macrocyclic organic ligand e.g. 18-crown-6 or cryptand [2.2.2]. The specific procedure enables the preparation of an unique alkali metal supramolecular complex forming in THE solution alkali metal ion pairs, e.g. K /L/K" (where L = 18-crown-6 or 15-crown-5). 

Such alkali metal ion pairs are capable of two electron transfer from the potassium anion towards a suitable substrate, e.g. p-butyrolactone with formation of a respective carbanion. The strong tendency to two electrons transfer is due to the unusual oxidation state of potassium anion bearing on its outer s orbital a labile electron doublet shielded from the positive potassium nucleus by inner orbitals. Using 5 -enantiometr of P-butyrolactone as a monomer and potassium supramolecular complex as catalyst, enolate carbanion is formed as the first reactive intermediate which induces polymerization, yielding poly-(R)-3-hydroxybutanoate. The resulting biomimetic polyester has the structure similar to native PHB produced in nature, except for acetoxy-end-groups, which are formed instead of the hydroxyl ones typical for natural PHB. 

Also, the base membrane used for ESA treatment contained 10 mol% AA segment, Srs for metal ion pair of Fe and Fe + of the modified membranes terminated with CTAC, CTAC/PAA/CTAC and CTAC/PAA/CTAC/PAA/CTAC ESA layers were 1.54+0.02, 1.75+0.07 and 2.10+0.06, respectively. 

It is commonly accepted [11] that the derivative (2.39), in case of the potential of metal/metal ions pair, is equal to the average oxidation number of metal ions in the electrolyte. Equation (2.40) shows that, if the potentials are measured at stationary but non-equilibrium condition, the oxidation number calculated in such way would be overstated. Also, it is easy to show that if the contribution from the reactions with the supporting electrolyte is essential and Eq. (2.37) is true, the method of calculation of average oxidation number would give even larger values. 

FIGURE 5.13 Ca-Fe(II) exchange isotherms (plotted as amount sorbed) on montmoril-lonite, a layered clay mineral (see Chapter 8). ( ) Ca + sorbed (0) Fe(II) sorbed lines nonpreference isotherms. (With kind permission from Springer Science+Business Media Aquat. Geochem., Charlet, L., C. Tournassat, Fe(II)-Na(I)-Ca(II) cation exchange on montmorillon-ite in chloride medium Evidence for preferential clay adsorption of chloride - metal ion pairs in seawater, 11, 2005, 115-137.)... 

Charlet, L., and C. Toumassat. 2005. Fe(II)-Na(I)-Ca(II) cation exchange on montmoriUonite in chloride medium Evidence for preferential clay adsorption of chloride-metal ion pairs in seawater. Aquatic Geochemistry 11, no. 2 115-137. 

The arrangement of ions is a major driving force in both solid and liquid salts, and crystallography is one of the only tools which can extract this information tmambiguously. While emphasis is placed on molecular stmcture identification, packing phenomena relevant to metal speciation and distribution in ILs were observed in each of the structures examined here. This is especially important when considering that the majority of solution chemistry is still based on a foundation of molecular systems where neutral species dominate and ions, if present, are considered dissociated. The phenomena observed here such as the formation of ion pairs with hydrophobic exteriors, the effect of outer-sphere interactions on metal-extractant stoichiometry, and the formation of mixed metal ion pairs, which are all still relatively unexplored even IL-based separations, may not even be observed in neutral systems. 

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