Anion and cation recognition by new mono- and bis-ruthenium(II) bipyridyl crown ether receptor molecules

Novel aza crown and dibenzocrown ether mono- and bis-ruthenium(II) bipyridyl amide-containing receptors have been synthesized and their preliminary Group 1 metal cation and halide anion complexing properties investigated. H-1 NMR coordination studies have shown the receptors bind potassium cations in their respective crown ether recognition sites. Chloride anion coordination studies reveal that those receptors containing secondary amide CO-NNH groups can complex and electrochemically sense chloride anions through a combination of electrostatic attraction and favourable amide CO-NH---anion hydrogen bonding interactions. Stability constant determinations from NMR titration data and electrochemical observations suggest, with receptor [Ru(2)L(6)(bipy)(4)][PF6](4), aza crown ether complexed potassium cations in combination with an amide-linked positively charged ruthenium(II) bipyridyl moiety can cooperatively enhance the strength of chloride anion complexation. In addition, fluorescence emission spectral studies show that the relative emission intensities of the metal-to-ligand charge transfer emission bands of the secondary amide-containing receptors are increased in the presence of chloride anions. Copyright (C) 1996 Elsevier Science Ltd