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.