Potential anion sensing properties by a redox and substitution series of [Ru(bpy)3-: N(Hdpa)n]2+, n = 1-3; Hdpa = 2,2′-dipyridylamine: Selective recognition and stoichiometric binding with cyanide and fluoride ions

Abstract

Three mononuclear ruthenium complexes of composition [Ru(bpy)3-n(Hdpa)n]2+, n = 1-3, where bpy = 2,2′-bipyridine, and Hdpa = 2,2′-dipyridylamine have been developed for selective recognition of cyanide (CN-) and fluoride (F-) ions. All the complexes have been characterised using standard analytical and spectroscopic techniques. The potential anion sensing features of complexes [1](ClO4)2, [2](ClO4)2 and [3](ClO4)2 have been thoroughly investigated by spectrophotometry, electrochemistry and 1H NMR spectroscopy using a wide variety of anions, such as F-, Cl-, Br-, PF6-, NO3-, ClO4-, HSO4-, AcO- and CN-. Cyclic voltammetry and differential pulse voltammetry established that [1](ClO4)2 and [2](ClO4)2 are excellent electrochemical sensors for the selective recognition of CN- and F- anions. The complexes display intense ligand-centred absorption bands in the UV region and moderately intense metal-to-ligand charge-transfer (MLCT) bands in the visible region. All the complexes act as selective colorimetric sensors for CN- and F- anions due to modulation of MLCT band position of the receptors in the presence of CN- or F- resulting distinct colour change visible by naked eyes. Further, emission quenching of 12+ and 22+ in the presence of CN-, F- and AcO- ions make them suitable luminescence-based sensors. The Stern-Volmer plot revealed static quenching mechanism of emission of the receptor 12+ in presence of cyanide and fluoride ions, while dynamic quenching dominates in case of AcO- anion. © 2016 The Royal Society of Chemistry.