Ab Initio Thermochemistry of the First-Row Transition Metal Tris(Acetylacetonates): Refined, Revisited, and Recommended

Gas-phase enthalpies of formation (Δ_f<i>H</i>°(g, 298 K)) of Sc, Ti, V, Cr, Mn, Fe, and Co tris(acetylacetonates) were predicted using the reaction-based approach implemented in the recently developed program. Energies of working reactions were computed by employing the Feller-Peterson-Dixon composite scheme in conjunction with the DLPNO-CCSD(T)/CBS and also using several DFT model chemistries. A careful analysis of the literature data on the experimental and theoretical Δ_f<i>H</i>° (g, 298 K) of the relevant transition metal oxides, fluorides, and chlorides revealed the most reliable values to be used as references in the reaction-based approach. The predicted enthalpies of formation of M(acac)₃ complexes were utilized for the rationalization of the literature-available experimental data. The difference between theoretical and experimental Δ_f<i>H</i>° (g, 298 K) falls within the error margins in the case of V(acac)₃, Fe(acac)₃, and Co(acac)₃. For Mn(acac)₃, the theoretical Δ_f<i>H</i>° (g, 298 K) agrees better with the value obtained from an older study. In the case of Sc(acac)₃ and Cr(acac)₃, the discrepancies between experiment and theory reach 13.1 and 6.1 kcal mol^-1, respectively. For Ti(acac)₃, the predicted Δ_f<i>H</i>° (g,298 K) = -374.8 ± 4.5 kcal mol^-1 is probably the only currently available value.