Osmium(II) mixed-chelate derived from imidazole 4,5-bis(benzimidazole) and 2,2′-bipyridine as multichannel sensor for anions: Synthesis, structural characterization and binding studies

Mixed-ligand complex of composition [(bpy)(2)Os(H(3)Imbzim)](ClO4)(2)center dot 2H(2)O (1), where H(3)Imbzim = 4,5-bis(benzimidazole-2-yl)imidazole and bpy = 2,2'-bipyridine, has been synthesized and characterized using standard analytical and spectroscopic techniques. The X-ray crystal structure of the complex has been determined which showed that it crystallized in triclinic form with the space group P-1. The anion binding properties of the complex has been thoroughly investigated in solution using absorption, emission, and H-1 NMR spectral measurements. The metalloreceptor acts as sensor for F-, AcO-, and to some extent for H2PO4- anions. Although at relatively lower concentration of anions the 1:1 H-bonded adduct is formed, in the presence of excess of anions deprotonation of the imidazole N-H fragments occurs which is accompanied by a distinct change of color. Double deprotonation is also observed in the presence of hydroxide. The binding affinities of different anions towards the receptors have been evaluated. Cyclic voltammetry measurements carried out in acetonitrile have provided evidence in favor of an anion-dependent electrochemical response of the receptor with F- and AcO- ions.