Anionic species characterizing crystalline

Catechol, with its more readily ionized protons (and other o-diphenols), in aqueous alkaline solution forms soluble, colourless anionic species. Stability constants for the 1 1 and 2 1 species have been measured (log X, = 7.5, log K2 = 5.7) and the 3 1 species forms at pH > 11. In 0.3 M NaOH, the latter is readily oxidized by ferricyanide to Mn,u. Some crystalline species have been described, but need further characterization and most seem to be very air sensitive.212,282 Again the interest in these compounds has been directed mainly towards their oxidation to Mn111 and MnIV species. 

These solids are characterized by cationic and anionic species that are associated through electrostatic interactions. All purely ionic salts possess crystalline structures. 

As mentioned in the Introduction, no structural information on these species was available for more than 40 years after the discovery of the first Zintl metal cluster anions, since no pure crystalline phases could be isolated and characterized structurally. Nevertheless, early efforts to rationalize the observed formulas and chemical bonding of these intermetallics and related molecules utilized the Zintl-Klemm concept [75, 76] and the Mooser-Pearson [77] extended (8 — N) rule. In this rule N refers to the number of valence electrons of the more electronegative metal (and thus anionic metal) in the intermetallic phases. 

Isopolytungstate anions isolated from solution in the form of crystalline salts are listed in Table 4. Several other species undoubtedly remain to be characterized, but analysis of aqueous polytungstate equilibria is complicated by the extreme range of rates involved. Many apparently stable isopolytungstates may be kinetic intermediates. For this reason, no equilibrium distribution diagrams, will be given, nor would such diagrams provide a useful... 

If a stoichiometric amount of alkali metal is used instead, in the case of E = Sn singly reduced species, the radical anion [Btp2Sn2] - (98) is formed as the predominant product. Depending on the employed alkali metal and donor-solvent present, three different crystalline compounds were obtained and structurally characterized 98a and 98b built from isolated ions132 and 98c comprising contact ion pairs with a Na—Sn bond133. The... 

Ammonia, alkylamines, and other proton acceptor species can react with boric acid in aqueous or alcoholic solutions to form a wide range of crystalline nomnetal borate salts. Borate salts of aprotic nomnetal cations, such as quaternary ammonium cations, have also been characterized. The ammonium borates are significant commercial products, and the recognition that both protic and aprotic nonmetal cations can stabilize unusual borate anions has led to increased interest in the study of this area. 

In continuing and most elegant studies, Mak and coworkers have exploited crystal engineering principles to capture and thereby stabilize hitherto rare or even uncharacterized species within a crystalline manifold.For example, monocyclic oxocarbon dianions C 0 for n = 3, 4, 5, and 6 have been characterized in this manner. As an illustrative example, the squarate dianion, 404 (Figure 26a), has been trapped in a crystal structure with formulation PiUN]2[C404 ]- 4(NH2)2C=S 2H20. The anions are located in a three-dimensional host lattice whereby zigzag... 

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