Protonated azacryptate hosts for nitrate and perchlorate

Abstract

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 ≈3.4 and ≈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 10³∶1.