Titanocene Selenide Sulfides Revisited: Formation, Stabilities, and NMR Spectroscopic Properties.

[TiCp₂S₅] (phase A), [TiCp₂Se₅] (phase F), and five solid solutions of mixed titanocene selenide sulfides [TiCp₂SexS₅-x] (Cp = C₅H₅-) with the initial Se:S ranging from 1:4 to 4:1 (phases B⁻E) were prepared by reduction of elemental sulfur or selenium or their mixtures by lithium triethylhydridoborate in thf followed by the treatment with titanocene dichloride [TiCp₂Cl₂]. Their 77Se and 13C NMR spectra were recorded from the CS₂ solution. The definite assignment of the 77Se NMR spectra was based on the PBE0/def2-TZVPP calculations of the 77Se chemical shifts and is supported by 13C NMR spectra of the samples. The following complexes in varying ratios were identified in the CS₂ solutions of the phases B⁻E: [TiCp₂Se₅] (5₁), [TiCp₂Se₄S] (4₁), [TiCp₂Se₃S₂] (3₁), [TiCp₂SSe₃S] (3₆), [TiCp₂SSe₂S₂] (2₅), [TiCp₂SSeS₃] (1₂), and [TiCp₂S₅] (0₁). The disorder scheme in the chalcogen atom positions of the phases B⁻E observed upon crystal structure determinations is consistent with the spectral assignment. The enthalpies of formation calculated for all twenty [TiCp₂SexS5-x] (x = 0⁻5) at DLPNO-CCSD(T)/CBS level including corrections for core-valence correlation and scalar relativistic, as well as spin-orbit coupling contributions indicated that within a given chemical composition, the isomers of most favourable enthalpy of formation were those, which were observed by 77Se and 13C NMR spectroscopy.