Ab initio characterization of the isomerism between the μ-η22-peroxo- and bis(μ-oxo)dicopper cores

Christopher J. Cramer, Bradley A. Smith, William B. Tolman

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The interconversion of model compounds {[(NH3)3Cu]2(μ-η22-O2)}2+ (1) and {[(NH3)3Cu]2(μ-O)2}2+ (2) has been examined using multireference second-order perturbation theory with an 8-electron/8-orbital active space. At this level of theory, 1 and 2 are separated by only 0.3 kcal/mol, and the barrier to isomerization is predicted to be very low based on single-point energy calculations for intermediate structures. The flat nature of the potential energy surface along the interconversion coordinate derives from a balancing of Coulomb forces and nondynamic electron correlation. The latter effect depends critically on the significant energy change experienced by the 13a(u) σ(oo)* virtual orbital on passing from one isomer to the other. In addition, solvation electrostatics favor 2 over 1.

Original languageEnglish (US)
Pages (from-to)11283-11287
Number of pages5
JournalJournal of the American Chemical Society
Issue number45
StatePublished - Nov 13 1996


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