Protonated azacryptate hosts for nitrate and perchlorate

Encapsulation of nitrate and perchlorate within two protonated cryptate hosts [H6L1](6+) and [H6L2](6+), as studied by potentiometric and NMR titration methods, showed dominant 1:1 complexation for both anions. Complexation constants, log K, with [H6L1](6+) and [H6L2](6+) are, generally, high at 3.7 and 3.4 for nitrate, and approximate to 3.4 and approximate to 2.5 for perchlorate, respectively. Good geometric complementarity was confirmed in the case of perchlorate and [H6L2](6+) by an X-ray crystallographic structure determination of the inclusive anion cryptate. For nitrate, there is evidence for 1:2 complexation in the presence of a large excess of anion, relative 1:1 and 1:2 complexation constants being in the approximate ratio 10(3):1.