TD-DFT assessment of UV-vis spectra palladium and platinum complexes with thiols and disulfides

Time-dependent density functional theory (TD-DFT) and spectrophotometric methods were used for speciation analysis in systems disulfides (cystine, cystamine, homocystine, 3,3-dithiodipropionic acid) - [PdCl₄]^2- or [PtCl₄]^2-. We use the M06-2X and CAM-B3LYP density functionals with Def2-SVP basis set to reproduce the experimental UV-vis spectra; the polarized continuum solvation model (PCM) was fitted to take into account solvation effects of the medium (water). Used methods have shown the good agrees with the experiment - theoretical values of transition energies differ from real parameters within ±0.15 eV for functional CAM-B3LYP. Binuclear disulfide complexes of Pd(II) with cystine and cystamine have form S,N-coordination sites, instead of S,S-conformation. It was shown that Pd(II) thiolate complexes formed by cleavage of the disulfide bond exist as [PdCl₃L] and [Pd₂S₂L₂]. Pt(II)-disulfide systems have confirmed the presence of [Pt₂Cl₆(R-SS-R)] and [PtCl₄(S-R)] complex species. The DFT/CAM-B3LYP/Def2-SVP/SMD level can be recommended for theoretical estimations of absorption spectra of complexes of palladium or platinum and sulfur-containing ligands.