Five density functionals including GGA (generalized gradient approximation) (BP86), meta-GGA (TPSS), hybrid meta-GGA (TPSSh), hybrid (B3LYP), and double-hybrid functionals (B2PLYP) were calibrated for the prediction of 57Fe Mössbauer isomer shifts on a set of 20 iron-containing molecules. The influence of scalar relativistic effects and the basis set dependence of the predictions were investigated.

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The use of redox mediators is a well-established approach in electrosynthesis to lower kinetic barriers, to improve product selectivity and to suppress electrode fouling.[1] Recently we have developed a new series of metal‐free and easy-to-synthesize redox mediators based on the phenanthro[9,10-d]imidazole framework (see figure below, left).[2] Upon anodic oxidation these compounds form stable radical cations which can be used to catalyze the oxidation of benzylic alcohols and ethers. By selection of a suitable substitution pattern the oxidation potential of the mediator can be adapted to the redox potential of a specific redox reaction. Our efforts are currently focused on the immobilization of alkyne-modified phenanthroimidazoles on carbon electrodes via Cu(I)-catalyzed azide-alkyne cycloaddition (see figure below, right). Our goal is to simplify the product separation after an electrolysis and to improve the long-term stability of the mediator. By attachment to the electrode surface we were able to increase the turnover numbers by several orders of magnitude while maintaining reasonable reaction rates. Further studies are directed towards a better understanding of the mechanism of the charge transfer between mediator and substrate as well as the chemical follow-up reactions. A combination of spectroelectrochemical experiments and computational studies will be used to discuss possible intermediates and transition states. References: [1] R. Francke, R. D. Little, Chem. Soc. Rev. 2014,43 , 2492. [2] R. Francke, R. D. Little, J. Am. Chem. Soc. 2014, 136, 427. Figure 1

This work reports on a novel computational approach to the efficient evaluation of one-electron coupling coefficients as they are required during spin-adapted electronic structure calculations of the configuration interaction type. The presented approach relies on the equivalence of the representation matrix of excitation operators in the basis of configuration state functions and the representation matrix of permutation operators in the basis of genealogical spin eigenfunctions. After the details of this connection are established for every class of one-electron excitation operator, a recursive scheme to evaluate permutation operator representations originally introduced by Yamanouchi and Kotani is recapitulated. On the basis of this scheme we have developed an efficient algorithm that allows the evaluation of all nonredundant coupling coefficients for systems with 20 unpaired electrons and a total spin of S = 0 within only a few hours on a simple Desktop-PC. Furthermore, a full-CI implementation that utilizes the presented approach to one-electron coupling coefficients is shown to perform well in terms of computational timings for CASCI calculations with comparably large active spaces. More importantly, however, this work paves the way to spin-adapted and configuration driven selected configuration interaction calculations with many unpaired electrons.

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