Synthesis and characterization of novel acyclic, macrocyclic, and calix[4]arene ruthenium(II) bipyridyl receptor molecules that recognize and sense anions

The Lewis acidic redox-active and photoactive ruthenium(II) bipyridyl moiety in combination with amide (CO-NH) groups has been incorporated into acyclic, macrocyclic, and lower rim calix[4]arene structural frameworks to produce a new class of anion receptor with the dual capability of sensing anionic guest species via electrochemical and optical methodologies. Single-crystal X-ray structures of (1)Cl and (11)H2PO4 reveal the importance of hydrogen bonding to the overall anion complexation process. In the former complex, six hydrogen bonds (two amide and four C-H groups) stabilize the Cl- anion and three hydrogen bonds (two amide and one calix[4]arene hydroxyl) effect H2PO4- complexation with 11. Proton NMR titration investigations in deuterated DMSO solutions reveal these receptors form strong and, in the case of the macrocyclic 5 and calix[4]arene-containing receptor 11, highly selective complexes with H2PO4-. Cyclic and square-wave voltammetric studies have demonstrated these receptors to electrochemically recognize Cl-, Br- H2PO4- and HSO4- anions. The calix[4]arene anion receptor 11 selectively electrochemically senses H2PO4- in the presence of 10-fold excess amounts of HSO4- and Cl-. Fluorescence emission spectral recognition of H2PO4- in DMSO solutions is displayed by 3, 5, and 11.