Ru(ii) and Os(ii) mixed-chelates derived from imidazole-4,5-dicarboxylic acid and 2,2′-bipyridine as colorimetric sensors for anions: synthesis, characterization and binding studies

Abstract

Mixed-ligand monometallic ruthenium(II) and osmium(II) complexes of composition [(bipy)₂M(H₂Imdc)](ClO₄), where H₃Imdc = imidazole-4,5-dicarboxylic acid and bipy = 2,2′–bipyridine, have been synthesized and characterized using standard analytical and spectroscopic techniques. The X-ray crystal structures of the ruthenium(II) complexes, [(bipy)₂Ru(H₂Imdc)](ClO₄) (1) and its corresponding N–H deprotonated form [(bipy)₂Ru(HImdc)] (3) have been determined. Compound 1 crystallizes in monoclinic form with space group P2₁/c while 3 is obtained in triclinic form with the space group P. The anion binding properties of the complexes 1 and 2 have been thoroughly investigated in acetonitrile solution using absorption, emission, and ¹H NMR spectral measurements. Both of the metalloreceptors act as sensors for F⁻, AcO⁻ and 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 fragment occurs and is accompanied by distinct change of colour. Cyclic voltammetry (CV) measurements carried out in acetonitrile have provided evidence in favour of anion-dependent electrochemical responses of 1 and 2 with F⁻ and AcO⁻ ions.