Anion–Anion Proton Transfer in Hydrogen Bonded Complexes

Abstract

Complexation of dihydrogen phosphate by an anion receptor containing six hydrogen bond donor groups has been shown to reduce the pK(a) of the bound anionic species to such an extent that addition of further aliquots of dihydrogen phosphate result in deprotonation of the bound species with the resultant formation of a monohydrogen phosphate receptor complex. X-ray crystallographic studies confirm monohydrogen phosphate complex formation in the solid state. In this way, this study explains the formation of complexes with unusual stoichiometries when investigating the binding of dihydrogenphosphate anion to hydrogen-bonding receptors.

Calix[4]pyrrole-based anion transporters with tuneable transport properties

“…The introduction of one triazole hydrogen bond 30 donor group into the strap results in an improvement of the affinity by a factor of 10 (entries 1, 4) however the incorporation of a second yields only a rather marginal gain (entry 13). Surprisingly the second triazole moiety scarcely contributes to the overall enthalpy of binding (entries 4 versus 35 13,19,25). Lengthening the distance between the triazole modules diminishes the enthalpic interaction, whilst concomitantly raising the entropic component to more positive values by an equivalent amount.…”

“…Another possibility is that trans-protonation occurs between bound and free anion as has been observed previously in 105 neutral hydrogen bond donor complexes with dihydrogen phosphate and bicarbonate. 19 If an interwoven network of hydrogen bonds is established upon binding acidic anions by compounds 4-6 then the dihydrogenphosphate anion may form such a network. It is 110 likely that subtle differences in the layout and spacing of the hydrogen bond donor and acceptor groups may result in profound effects on the stability of the complex as the number of optimally aligned structural arrangements of one host and one guest species are severely limited.…”

Cholesterol appended pyridinium ureas: a case of gel making and breaking for selective visual readout of F−

“…Further addition of H 2 PO 4 − caused an increase in emission which was assumed to be due to decomplexation (See ESI †). 8 Fig. 2 represents the change in fluorescence ratio of 1 at 430 nm, upon addition of 10 equiv.…”

A new benzimidazolium receptor for fluorescence sensing of iodide

“…Figure 2 represents the change in fluorescence of 1 upon addition of 2 equivalent amounts of a particular anion. Upon addition is presumably attributed to the deprotonation of the bound dihydrogen phosphate with the resultant formation of the monohydrogen phosphate receptor complex, as described by Gale et al (21). In the process, partial decomplexation of H 2 PO 2 4 cannot be neglected.…”