Mononegative oxoanions

NMR titrations (of anion into ligand at fixed pH) and pH-potentiometric titrations (of pH at fixed anion ligand ratios) provide comparable values of the stability constants for binding of mononegative oxoanions by protonated R3Bm, R3F, and R3P hosts [15,20,21] Table 2. The weak complexation at hexaprotonated levels for tetrahedral monoanionic oxoanions makes it difficult to obtain reliable data for protonation levels below 5. This has however been achieved for nitrate with the cleft binding host R3P as well as for Re O4 with the most basic cryptand R3Bm. 

TABLE 2. Stepwise formation for binding of mononegative oxoanions... 

Complexation constants for binding of mono- and di-negative oxoanions by the cryptands can be determined by pH-potentiometry. For the more weakly-binding mononegative systems, NMR shifts can provide complementary information. For these studies we use the large size-excluded tosylate anion as the supporting electrolyte and all log K values are thus relative to this notional standard [19],... 

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