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.

Mixed-ligand monometallic ruthenium(II) and osmium(II) complexes of composition [(bipy)(2)M(H(2)Imdc)](ClO(4)), where H(3)Imdc = 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)(2)Ru(H(2)Imdc)](ClO(4)) (1) and its corresponding N-H deprotonated form [(bipy)(2)Ru(HImdc)] (3) have been determined. Compound 1 crystallizes in monoclinic form with space group P2(1)/c while 3 is obtained in triclinic form with the space group P1. The anion binding properties of the complexes 1 and 2 have been thoroughly investigated in acetonitrile solution using absorption, emission, and (1)H NMR spectral measurements. Both of the metalloreceptors act as sensors for F(-), AcO(-) and H(2)PO(4)(-) 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.