Density Functional Study of Electron Paramagnetic Resonance Parameters and Spin Density Distributions of Dicopper(I) Complexes with Bridging Azo and Tetrazine Radical-Anion Ligands

Abstract

There exists a growing class of dinuclear complexes with bridging radical-anion ligands that is of interest both for bioinorganic and for supermolecular chemistry. Their bonding situation as well as chemical and spectroscopic properties are not described adequately by standard models such as the ligand-field theory. For rational design of complexes with desired properties, it is thus necessary to understand better the interrelations between electronic structure, spin density, and electron paramagnetic resonance (EPR) parameters in dinuclear systems with redox-active bridging ligands and to evaluate the performance of density functional methods in their description. As particularly suitable, experimentally well-characterized representatives, a series of dinuclear copper(I) complexes with azo or tetrazine bridge ligands have been studied here by different density functional methods. To reproduce the available experimental metal hyperfine couplings, the inclusion of spin-orbit effects into the calculations is necessary. An unusual direction of the dependence of computed hyperfine couplings on an exact-exchange admixture into the exchange-correlation functional may be understood from a McConnell-type spin polarization of the sigma-framework of the bridge. Ligand nitrogen hyperfine couplings are also compared with experiment where available. Electronic g-tensors are reproduced well by the calculations and have been analyzed in detail in terms of atomic spin-orbit contributions and electronic excitations.

Relativistic two-component calculations of electronic g-tensor for oxo-molybdenum(V) and oxo-tungsten(V) complexes: The important role of higher-order spin-orbit contributions

“…DFT calculations have been done either at the generalized-gradient-approximation (GGA) level, with the Becke exchange and Perdew correlation functionals (BP86) [30][31][32], or employing Becke's three-parameter hybrid functional with Perdew-Wang GGA correlation (B3PW91) [33][34][35][36]. As in most of our previous studies on EPR parameters of transition metal complexes [26,27,[37][38][39][40][41][42][43][44] the best agreement with experimental data for both hyperfine and g-tensors was obtained with hybrid functionals containing approximately 30-40% Hartree-Fock exchange, we have also evaluated the use of the oneparameter BPW91-40HF functional of the form E hybrid…”

A DFT study of EPR parameters in Cu(ii) complexes of the octarepeat region of the prion protein

“…43,44 Recently, the dependence of EPR parameters on the choice of the exchange and correlation functionals was also investigated for dinuclear copper(I) complexes with radical-anion ligands. 45 Table 1 reports the Cu-N and Cu-O distances calculated at the different levels of theory, as well as the hcc values of 63 Cu. Regarding molecular structures, values for Cu-N distances obtained using different functionals are very similar, and almost identical to the values in ref.…”

Comparison of Density Functional and Correlated Wave Function Methods for the Prediction of Cu(II) Hyperfine Coupling Constants

“…These differences in coordination chemistry provide a complete set of small mononuclear Cu(II) complexes. Other systems have been studied such as zeolite cluster models, [25] protein active sites, [26][27] or dinuclear Cu(I) complexes with ligand-radical nature, [28] but these fall outside of the scope of this work in terms of defining a benchmark set. Compared to previous work, [12,17] we emphasize that the members of the present test set have been independently curated for both their experimental structures and their EPR parameters.…”