Anion recognition through hydrogen bonding by adamantane-dipyrromethane receptors

Abstract

Adamantane-dipyrromethane (AdD) receptors [di(pyrrole-2-yl)methyladamantane ( 1), 2,2-di(pyrrole-2-yl)adamantane ( 2), 1,3-bis[di(pyrrole-2-yl)methyl]adamantane ( 3), 2,2,6,6-tetra(pyrrole-2-yl)adamantane ( 4)] form complexes with F −, Cl −, Br −, AcO −, NO 3 −, HSO 4 −, and H 2PO 4 −. The association constants of the complexes were determined by 1H NMR titrations, whereas the geometries of complexes 1·F − (2:1), 2·F − (2:1), 2·Cl − (2:1), 2·AcO − (2:1), and 4·F − (1:1) were determined by X-ray structural analysis. The most stable complexes are of 2:1 stoichiometry with F − and AcO −. The stability constants are in accordance with the anion basicity and the ability of AdD receptors to place the hydrogen bonding donor groups in a tetrahedral fashion around anions. The binding energies of the complexes between receptors 1– 4 and F − anion are calculated using quantum chemical methods. The calculated results show that the solvent polarity is important for the complexation of fluoride ion with AdD receptors 1– 4.