Anion Selective Recognition and Sensing by Novel Macrocyclic Transition Metal Receptor Systems. 1H NMR, Electrochemical, and Photophysical Investigations

A series of novel redox-active and photoactive ruthenium(II) and osmium(II) bipyridyl-, ferrocene-, and cobaltocenium-containing macrocyclic receptors with the dual capability of selectively sensing anionic guest species via electrochemical and optical methodologies have been prepared. Single-crystal X-ray structures of 7·Cl-, 7·2Br-, and 13·2OAc- highlight the importance of hydrogen bonding and respective macrocyclic cavity size to the anion recognition process in the solid state. Proton NMR titration studies in deuterated DMSO solutions reveal these receptors form strong and remarkably selective complexes with Cl-, H2PO4 -, and OAc- anions dependent upon the flexibility, topology, and size of the receptor cavity. Cyclic and square-wave voltammetric investigations have demonstrated these receptors to electrochemically recognize Cl-, H2PO4 -, and OAc- anions. Photophysical studies reveal emission spectral recognition of Cl- in acetonitrile solutions is displayed by 7−12. With the hetero-dinuclear receptors 8, 9, and 12, the rate constants of the energy transfer process responsible for the quenching of the luminescent ruthenium excited state significantly decreased in the presence of chloride anion.