Size and temperature dependent encapsulation of tetrahedral anions by a protonated cryptand host

Abstract

The protonated cryptand L shows both size and temperature dependent encapsulation for tetrahedral ClO4− and H2PO4− anions (L = N[(CH2)2NHCH2(C6H4-p)CH2NH(CH2)2]3N). The crystal structures of perchlorate complex [(H6L)(ClO4)][ClO4]5(H2O)7(CH3CN) (1) and phosphate complex [(H8L)(H2O)3][H2PO4]8(H2O)9 (2) showed that the smaller ClO4− can facilely enter into the cavity of H6L6+, while the larger H2PO4− can not be encapsulated inside the cavity of H6L6+ and H8L8+ at room temperature. Upon heating, however, H2PO4− can be encapsulated into the cavity of H8L8+ to generate a complex of [(H8L)(H2PO4)][H2PO4]7(H2O)18 (3), and the encapsulated H2PO4− can be released by increasing the pH value to 2.