Colorimetric fluoride detection in dimethyl sulfoxide using a heteroleptic ruthenium(ii) complex with amino and amide groups: X-ray crystallographic and spectroscopic analyses?

RSC Advances Pub Date: 2022-09-07 DOI: 10.1039/D2RA03593F

Abstract

A bis-heteroleptic ruthenium(II) complex, [Ru(Hdpa)2(H2pia)]X2 (1·X2; X = Cl, OTf, or F; Hdpa = di-2-pyridylamine; H2pia = 2-pycolinamide; OTf? = CF3SO3?), was synthesized and spectroscopically and crystallographically characterized. The crystal structures of 1·Cl2·2.5H2O and 1·F2·2EtOH revealed essentially identical geometries for the 12+ 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·F2·2EtOH, 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 NH2 group of the H2pia ligand in 12+ acted as receptors for F? anion recognition via 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-n-butylammonium fluoride to the red DMSO solution of 1·(OTf)2·H2O, the solution turned dark brown. 1H NMR analysis and absorption spectroscopy of the reaction between 12+ 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 H2pia, although they were in different environments in the DMSO solution. A tris-F-adduct with 12+, 1·F3?, was formed when sufficient F? anions were present in the solution, despite the presence of four NH protons in 12+. Time-dependent DFT calculations of 12+ and 1·F3? were consistent with their absorption spectra.

Graphical abstract: Colorimetric fluoride detection in dimethyl sulfoxide using a heteroleptic ruthenium(ii) complex with amino and amide groups: X-ray crystallographic and spectroscopic analyses
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