Spectral and electrochemical recognition of halide anions by acyclic mononuclear ruthenium(II) bipyridyl receptor molecules

New acyclic mononuclear ruthenium(II) bipyridyl amide receptors containing phenolic and sterically bulky tert-butyl pendant arms have been prepared and characterised. Spectroscopic and electrochemical anion-co-ordination studies have shown these receptors to bind chloride, bromide and iodide anions via a combination of electrostatic attraction and favourable amide CONH and phenolic ROH hydrogen-bonding interactions. Stability constant determinations from NMR titration data and electrochemical observations indicate that the presence of additional phenolic hydrogen-bonding units significantly enhances the strength of anion complexion. In addition, incorporation of sterically bulky tert-butyl groups to the amide units confers improved selectivity for chloride over iodide anions. Fluorescence-emission spectroscopic studies show that the relative emission intensities of the metal-to-ligand charge-transfer emission bands of the receptors is enhanced in the presence of chloride and bromide but diminished by iodide anions.