Colorimetric Fluoride Detection in Dimethyl Sulfoxide Using a Heteroleptic Ruthenium(ii) Complex with Amino and Amide Groups: X-ray Crystallographic and Spectroscopic Analyses

A bis-heteroleptic ruthenium(ii) complex, [Ru(Hdpa)(Hpia)]X (1·X; X = Cl, OTf, or F; Hdpa = di-2-pyridylamine; Hpia = 2-pycolinamide; OTf = CFSO ), was synthesized and spectroscopically and crystallographically characterized. The crystal structures of 1·Cl·2.5HO and 1·F·2EtOH revealed essentially identical geometries for the 1 dication; however, the dihedral angle between the two pyridyl groups in the Hdpa ligands, which represented the degree of bending of the bent conformation, was affected by hydrogen-bonding interactions between the NH group and counterions. In 1·F·2EtOH, one of the Hdpa ligands had an unusually smaller dihedral angle (15.8°) than the others (29.9°-35.0°). The two NH groups of each Hdpa ligand and the NH group of the Hpia ligand in 1 acted as receptors for F anion recognition hydrogen-bonding interactions in a dimethyl sulfoxide (DMSO) solution, and the reaction showed an unambiguous color change in the visible region. Upon the addition of tetra--butylammonium fluoride to the red DMSO solution of 1·(OTf)·HO, the solution turned dark brown. H NMR analysis and absorption spectroscopy of the reaction between 1 and the added F anions revealed that the F anions did not distinguish between the two amino groups of Hdpa and the amide group of Hpia, although they were in different environments in the DMSO solution. A tris-F-adduct with 1, 1·F , was formed when sufficient F anions were present in the solution, despite the presence of four NH protons in 1. Time-dependent DFT calculations of 1 and 1·F were consistent with their absorption spectra.