ChemInform Abstract: On the Nature of Homo‐ and Hetero‐Dinuclear Metal—Metal Quadruple Bonds — Analysis of the Bonding Situation and Benchmarking DFT Against Wave Function Methods.

Abstract

Homo- and hetero-dimetallic (d–d)8 analogues of the formally quadruply bonded [Re2Cl8]2– system with the general formula [MM′Cl8]x (M, M′ = Tc, Re, Ru, Os, Rh, Ir and x = –2, –1, 0, +1, +2) have been calculated with the density functional theory (DFT) functionals SVWN, BLYP, BP86, PBE, OLYP, OPBE, HCTH, B3LYP, O3LYP, X3LYP, BH&HLYP, TPSS, VSXC, TPPSh, and ab initio methods (CASPT2, CCSD(T)) using basis sets of triple-ζ quality. The performance of the functionals for the description of the metal–metal bond distance and the bond dissociation energy as well as the singlet–triplet gap was evaluated with respect to ab initio data at the CASPT2 level. Generally, the generalized gradient approximation (GGA) functionals, BLYP, BP86, and PBE, show good performance in the description of the metal–metal bond distance and for the dissociation energy. Hybrid functionals are not to be used for compounds of the type discussed here as they lead to increasingly too short and too weak bonds with the amount of exact exchang...