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

Gas-phase enthalpies of formation (ΔfH°(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 ΔfH° (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 ΔfH° (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 ΔfH° (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 ΔfH° (g,298 K) = -374.8 ± 4.5 kcal mol-1 is probably the only currently available value.