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

• Published in: RSC advances 2022-09, Vol.12 (39), p.25227-25239
• Main Authors: Toyama, Mari, Hasegawa, Tomoki, Nagao, Noriharu
• Format: Article
• Language: English
• Subjects: Absorption spectra; Anions; Chemistry; Colorimetry; Crystal structure; Crystallography; Dihedral angle; Dimethyl sulfoxide; Fluorides; Hydrogen bonding; Ligands; NMR; Nuclear magnetic resonance; Ruthenium; Ruthenium compounds; Spectrum analysis; Sulfoxides
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d2ra03593f

A bis-heteroleptic ruthenium( ii ) complex, [Ru(Hdpa) 2 (H 2 pia)]X 2 ( 1 ·X 2 ; X = Cl, OTf, or F; Hdpa = di-2-pyridylamine; H 2 pia = 2-pycolinamide; OTf − = CF 3 SO 3 − ), was synthesized and spectroscopically and crystallographically characterized. The crystal structures of 1 ·Cl 2 ·2.5H 2 O and 1 ·F 2 ·2EtOH revealed essentially identical geometries for the 1 2+ 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 2 ·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 2 group of the H 2 pia ligand in 1 2+ 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 ·H 2 O, the solution turned dark brown. 1 H NMR analysis and absorption spectroscopy of the reaction between 1 2+ 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 H 2 pia, although they were in different environments in the DMSO solution. A tris-F-adduct with 1 2+ , 1 ·F 3 − , was formed when sufficient F − anions were present in the solution, despite the presence of four NH protons in 1 2+ . Time-dependent DFT calculations of 1 2+ and 1 ·F 3 − were consistent with their absorption spectra. A bis-heteroleptic ruthenium( ii ) complex; [Ru(Hdpa) 2 (H 2 pia)]X 2 ( 1 ·X 2 ; X = Cl, OTf, or F; Hdpa = di-2-pyridylamine; H 2 pia = 2-pycolinamide; OTf - = CF 3 SO 3 - ) was synthesized and spectroscopically and crystallographically characterized.