Polyanionic species

Binary compounds with metals are generally of low ionic character. Many those with transition metals have the NiAs and related structures and show metallic properties. Some compounds appear to contain polyanionic species (e.g., P24- isoelectronic with S22- in Sr2P2 and P73- in Na3P7), although the bonding is certainly not fully ionic. 

The precipitation of the hydroxides can be performed either starting from an alkaline solution which is acidified, or from acidic solutions by raising the pH. In the first case, the formation of the solid product proceeds via polyanionic species. These polyanionic species undergo condensation reactions, either via ola-tion reactions... 

DyNAs, dynamic analogs of nucleic acids, were obtained as cationic main-chain dynamers bearing nucleobase groups and were shown to interact with polyanionic species displaying a marked increase in size with the negative charge of the substrate, thus demonstrating their adaptive character (Fig. 9) [69]. 

Films of oxides can be produced by anodization of metal electrodes. For example, AI2O3 forms on an aluminum anode immersed in a solution of H3PO4. The thickness of the film can be controlled by the applied potential and the time of anodization. Such a film can be used as a support for other materials, such as poly(vinylpyridine) (PVP). Oxide films of other metals, such as Ti, W, and Ta, can be produced in a similar way. Oxide films can also be produced by CVD, vacuum evaporation and sputtering, and deposition from colloidal solution. Related inorganic films are those of polyoxometallates (iso- and heteropolyacids and their salts) (20). For example, the heteropolyanion P2W17M0O62K6 shows a number of reduction waves at a glassy carbon electrode. A wide variety of metallic polyanionic species (e.g., of W, Mo, V) exist and have a rich chemistry. Films of such materials are interesting for their electrocatalytic possibilities. 

Polyanionic species stablized by sulphonyl residues have seen continued development in the last twelve months. y-Alkylation of (111) is possible only when both a -protons have been removed to give a trianionic species. Interestingly when the isomeric ketosulphone... 

Dianion Generation. Lithium naphthalenide efficiently de-protonates alkynyloxy " and carboxylate anions (eq 5). In addition, the previously mentioned phenomenon of reductive metalation has been exploited to access dianions fromhalohydrins, -halo carboxylic acids, and -halo carboxamides, and even trianions from -dihalo alcohols. A major pathway for the polyanionic species is -elimination (eq 6) when such processes can be avoided, the polyanions react according to Hauser s rule (eq... 

The alkylation of secondary amides, on carbon, usually requires either -protection or the generation of a polyanionic species. Benzamidoacetone undergoes deprotonation to give a monoanion that... 

Similar phenomena may be invoked in the case of molybdenum, for which polyanionic species like Mo7024 " and Mog02 " were shown to coexist with numerous other species of lower nuclearity, depending on the pH, die molybdenum concentration and the temperature [4-6]. Differences in the ionic charges carried by these entities and in dieir molecular sizes modify Ue electrostatic intraaction with the support and the accessibility of the potential adsorption sites... 

Mono- and polyanionic species were obtained through deprotonation reactions of cyclobutadienes by excesses of methyllithium. The dianionic complex readily rearranged to a cobaltacyclopentadienyl unit (Scheme 44). ... 

In another example, polyanionic species can give a hydrogel in the presence of complexing iron species. However, the mechanical properties of the hydrogel are very dependent on the oxidation state of the iron ions, leading to reversible electrochemical switching of the gel s mechanical properties (Fig. 37) [373]. 

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