Ruthenium(II) dimethylsulfoxide complex with pyrazole/dithiocarbazate ligand

The aim of the study was to synthesize and characterize a new ruthenium(II)-pyrazole/dithiocarbazate complex derived from cis-[RuCl₂(dmso)₄] (Ru-dmso) and coordinated with 3-methyl-5-phenyl-pyrazoline-1-(S-benzyl)dithiocarbazate (dtc). The reaction of Ru-dmso with the dtc ligand was performed with equimolar amount, resulting in a neutral monosubstituted complex [RuCl₂(dmso)₃(dtc)] (Ru-dtc).To characterize this complex, conductivity measurements and spectroscopic techniques (¹H-NMR, FTIR, UV–Vis, ESI–MS) were applied. Thermogravimetric analysis (TG) and differential thermal analysis were used to identify the changes in the thermal decompositions. The molar conductivity in methanol indicates that this complex is nonelectrolyte. Mass spectra showed m/z peak at 697, with a typical isotope pattern of ruthenium, which can be assigned to fragments of [RuCl(dmso)₃(dtc)]⁺. The chemical shifts of dmso resonances in both ruthenium complexes have been compared and indicated that O-dmso from the precursor was substituted by the dithiocarbazate derivative in the Ru-dtc. The FTIR spectrum shows that this coordination was achieved through the N-pyrazole ring. Moreover, spectrophotometric titrations by the addition of increasing concentrations of triethanolamine or acetic acid to the dtc ligand and Ru-dtc complex enabled the determination of constant equilibrium from the absorbance changes in the visible band region. Moreover, density functional theory (DFT) calculations were applied to evaluate the electronic properties, while time-dependent DFT was applied to clarify UV–Vis results. Finally, the thermal data reveal various steps of decomposition of the ruthenium complexes, producing RuO₂ as final residue.