EHF theory of chemical reactions V. Nature of manganese-oxygen bonds by hybrid density functional theory (DFT) and coupled-cluster (CC) methods

Hybrid density functional theory (DFT) and post-Hartree-Fock methods are co mpared by depicting potential energy curves of the O-O dissociation of hydr operoxide and the M-O dissociation of transition-metal oxides. The former a pproach includes BLYP, B2LYP, B3LYP, and more general hybrid DFT methods, w hile the unrestricted Hartree-Fock (UHF) coulpled-cluster (UCC) SD(T) metho d is considered as the latter approach. The hybrid DFT methods can reproduc e the potential curve of the O-O dissociation process and the dissociation energy of HOOH by UCCSD(T). The methods are also useful for depicting poten tial curves of copper oxide (CuO) and manganese oxide (MnO), and reproduce the experimental M-O binding energies. The nature of Mn-O bonds in the nake d Mn-O, Mn-O porphyrine system and model complexes, XH3Mn(IV)O2Mn(IV)H3Y (X , Y = O, H), are examined in relation to the possible mechanisms of oxygena tion reactions. It is found that the radical character of Mn-O bonds increa ses with the increase of the oxidation number of the Mn ion in these system s. (C) 2001 John Wiley & Sons, Inc.