Performance of Density Functional Theory and Møller-Plesset Second-Order Perturbation Theory for Structural...

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(η(5)-Cp*)(η(3)-CH2CHCHC6H5)(NCCH3)2](2+) and the molecules RuO4 and Ru(C2O4)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(C2O4)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.