Synthesis, spectroscopic characterization, and DFT analysis of dichlorido(η6-p-cymene)ruthenium(II) complexes with isonicotinate-polyethylene glycol ester ligands

Ruthenium complexes have gained significant attention due to ruthenium similarity to iron, lower toxicity, and higher anticancer effectiveness than other compounds. In this contribution, five new isonicotinate-polyethylene glycol ester ligands were synthesized and characterized by NMR and IR spectroscopies. The corresponding Ru(II) complexes were also obtained, and their structure was elucidated by traditional methods. The optimization of structures was performed at B3LYP/6-31+G(d,p) level of theory for H, C, N, and O atoms and B3LYP/LanL2DZ for Ru. The intramolecular stabilization interactions were assessed through the Natural Bond Orbital approach. The NMR chemical shifts were predicted by the GIAO method and compared to the experimental values. High correlation coefficients and low mean absolute errors between these data sets proved that the predicted structure described well the experimental one. The theoretical and experimental IR spectra were also compared, and differences in the most notable bands were described. One of the ligands (L5) and complexes (5) showed fluorescent properties due to methylisatoic moiety. The electronic spectra of this compound were modeled by the TD-DFT method. The difference of 11 nm between experimental and theoretical wavelength was explained by the interactions between solvent and solute. Further biological and theoretical studies are advised for this series of compounds.