Performance of density functional theory and Møller-Plesset second-order perturbation theory for structural parameters in complexes of Ru

We assess the performance of density functional theory (DFT) and Møller-Plesset second-order perturbation theory (MP2) for predicting structural parameters in Ru complexes, in particular, a Ru(IV) allyl dicationic complex with the formula [Ru(?⁵-Cp*)(η³-CH ₂CHCHC₆H₅)(NCCH₃)₂] ²⁺ and the molecules RuO₄ and Ru(C₂O ₄)₂(H₂O)₂^-, where Cp* denotes C₅Me₅ and Me denotes methyl. The density functionals studied are B3LYP, B3PW91, M05, M06, M06-L, MOHLYP, MPW3LYP, PBE0, PW6B95, SOGGA, τHCTHhyb, ωB97X, and ωB97X-D, in combination with three different basis sets, namely, LANL2DZ, def2-SVP, and def2-TZVP. The theoretically computed Ru-C distances corresponding to the phenylallyl complex are especially well predicted by the SOGGA (pure DFT) and ωB97X-D (DFT plus an empirical molecular mechanics term) methods. This contrasts with an article in this Journal [Calhorda, M. J., Pregosin, P. S., and Veiros, L. F.J. Chem. Theory Comput. 2007, 3, 665-670] in which it was found that DFT cannot account for these Ru-C distances. Averaging over four Ru-C distances in the allyl complex and three unique Ru-O distances in RuO₄ and Ru(C ₂O₄)₂(H₂O)₂^-, the SOGGA and ωB97X-D methods have both a smaller mean unsigned error than MP2 and the same maximum error. The M06, PW6B95, PBE0, M06-L, and ωB97X density functionals also have a smaller or the same mean unsigned error as MP2.