Determination of oxidation states based on single-crystal diffraction experiments

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The oxidation state of an element is a central concept for understanding its chemical properties. However, it is not directly accessible. Even indirect evaluation through complex experimental setups are often limited or can only be applied to certain elements. In this project, a new procedure employing dispersion correction will be implemented in routine software for analyses of single crystal X-ray diffraction experiments, to enable the use of routine lab-equipment for the determination of oxidation states. This new software will rely on multi-wavelength experiments to obtain the shift of dispersion spectra of a given element with respect to the corresponding neutral atom to derive its oxidation state. The required calculations and refinements are carried out using Non-Spherical-Atoms in Olex2 (“NoSpherA2”). This is a software developed in parts by me in a previous project, which allows the use of tailor-made atomic form factors based on quantum chemical calculations of the electron density of the crystal structure at hand. An additional implementation of the “Resolution of Identity” and the “Effective Core potentials” is planned. Both techniques are well established in quantum chemistry to speed up wavefunction calculations. Thereby the computational time required during non-spherical form factor derivation will be brought to a scale and practicability for routine application. Employing crystal samples from current research projects of collaborators, the practical accuracy and reliability of the new methods will be evaluated. The main class of substances for this investigation will be catalytically and photo-redox active molecules. The latter are to be also examined in their excited state, using an experimental setup, which allows additional irradiation during the diffraction experiment. This will give access to the differences in dispersion and electronic structure between the excited and ground state crystal structure.