Bis‐μ‐oxo and μ‐η²:η²‐peroxo dicopper complexes studied within (time‐dependent) density‐functional and many‐body perturbation theory

Abstract

Based on the equilibrium geometries of [Cu2(dbdmed)2O2](2+) and [Cu2(en)2O2](2+) obtained within density-functional theory, we investigate their molecular electronic structure and optical response. Thereby results from occupation-constrained as well as time-dependent DFT (ΔSCF and TDDFT) are compared with Green's function-based approaches within many-body perturbation theory such as the GW approximation (GWA) to the quasiparticle energies and the Bethe-Salpeter equation (BSE) approach to the optical absorption. Concerning the ground-state energies and geometries, no clear trend with respect to the amount of exact exchange in the DFT calculations is found, and a strong dependence on the basis sets is to be noted. They affect the energy difference between bis-μ-oxo and μ-η(2):η(2)-peroxo complexes by as much as 0.8 eV (18 kcal/mol). Even stronger, up to 5 eV is the influence of the exchange-correlation functional on the gap values obtained from the Kohn-Sham eigenvalues. Not only the value itself but also the trends observed upon the bis-μ-oxo to μ-η(2):η(2)-peroxo transition are affected. In contrast, excitation energies obtained from ΔSCF and TDDFT are comparatively robust with respect to the details of the calculations. Noteworthy, in particular, is the near quantitative agreement between TDDFT and GWA+BSE for the optical spectra of [Cu2(en)2O2](2+).

Transition Metal Complexes and the Activation of Dioxygen

“…Two recent contributions exclusively use theoretical approaches to tackle issues associated with the properties of (μ-η Following up on previous work that underlined the difficulties associated with using theory to understand the electronic structural properties and relative stabilities of these cores [350,351], a further evaluation of the reliability of various functionals was reported [352]. The results confirmed that no single functional is optimal for describing systems with different supporting ligands.…”

Geometrical and optical benchmarking of copper(II) guanidine–quinoline complexes: Insights from TD‐DFT and many‐body perturbation theory (part II)

“…Thereby, all electron–hole pairs within an energy window of 18 eV are taken into account. The calculations are on the same footing as in our previous studies . Finally, we perform ΔSCF calculations for the energetically lowest optical excitation, that is, derive its energy from two separate self‐consistent‐field calculations, see, for example, Ref.…”

The Cu2O2torture track for a real-life system: [Cu2(btmgp)2O2]2+oxo and peroxo species in density functional calculations†

“…As far as we know, the transition between the two isomers O and P with realistic ligands has by now only been modelled using tridentate bis(pyrazolyl)pyridinylmethanes, as they stabilize a catalytically active model . Bidentate N donor ligands also stabilize P and O cores, but their theoretical treatment is even more complicated and the spectroscopic predictability limited . Here, guanidines have proven to be very useful for the stabilization of Cu 2 O 2 species .…”