Intern
Prof. Dr. U. Schatzschneider

DFT Calculations

Computational chemistry

Modern theoretical electronic structure methods, in particular those based on density functional theory (DFT), allow facile optimization of geometries and calculation of a wide range of molecular properties. Although not involved in method development, the Schatzschneider group routinely applies theoretical calculations to assist in the interpretation of experimental data and guide the synthesis of novel molecules by prediction of molecular properties.

Due to its facile use, high performance, and ability to predict a large number of spectroscopic parameters at different levels of theory, most of our work uses the ORCA program package from the group of Prof. Dr. Frank Neese at the Max-Planck-Institute for Chemical Energy Conversion (MPI CEC) in Mülheim/Ruhr.

Calculations are run on the Linux Cluster of the Leibniz Supercomputing Centre (LRZ) in Munich. Below, there is an overview of current and past applications of DFT calculation in our research.

Conformational preferences

In addition to the metal-ligand interactions in the inner coordination sphere of our metal complexes, we are particularly also interested in the orientation of functional groups at the outer ligand periphery, which are important to rationalise the interaction of such systems with bio(macro)molecules. DFT calculations are a facile means to study the conformational preference of organometal and coordination compounds and ORCA offers an easy way to map the energy hypersurface of given molecules.

The change in energy upon rotation around the Mn-N axis was calculated using DFT in a manganese(I) triazolate complex. Since the energy barrier is < 2 kcal mol-1, the five-membered ring can rotate freely around the Mn-N axis.

UV/Vis and vibrational spectroscopy

Vibrational band positions and UV/Vis electronic excitations can be calculated with high accuracy using DFT and TDDFT methods. In our current work, we particularly utilize such calculations to rationalise the factors which govern efficient photoinduced ligand release in our small-signalling molecules project and the assignment of intermediates in the CO release from metal carbonyl complexes by comparison with the vibrational signature of transient species observed in time-resolved pump-probe spectroscopy.

TDDFT-calculated difference density upon electronic excitation of a CO-releasing molecule (CORM). The red colour indicates a decrease in electron density upon excitation, the green colour highlights an increased electron density. The transition shown obviously is a metal-to-ligand charge transfer (MLCT).

Mössbauer parameters

The 57Fe Mössbauer isomer shift and quadrupole splitting is a very sensitive indicator of the number of d electrons, spin state, and coordination environment of the metal center. In a recent collaboration with the group of Ulf-Peter Apfel at the Ruhr-Universität Bochum, we have calculated these parameters using DFT for a range of dinitrosyl iron complexes (DNICs). An excellent agreement of calculated values with experimental data was found for the isomer shift, while the quadrupole splitting was more difficult to model accurately. Such compounds also have relevance in the context of small molecule signalling.

Spin densities and exchange coupling constants

The interest of Prof. Schatzschneider in stable radical ligands can be traced back to his doctoral thesis project in the group of Prof. Dr. Eva Rentschler, at that time at the Max-Planck-Institute for Bioinorganic Chemistry in Mülheim/Ruhr. Since then, we have continued to utilized DFT calculations for an insight in the spin density distribution in open-shell molecules and the calculation of the exchange coupling parameter J indicative of either ferro- or antiferromagnetic interactions in multi-spin systems.

The spin density distribution in a metal-radical complex with an open-shell nitronyl nitroxide (NIT) ligand coordinated to a dinuclear metal complex unit was calculated with DFT.