Manganese K-Edge X-Ray Absorption Spectroscopy as a Probe of the Metal-Ligand Interactions in Coordination Compounds

A series of manganese coordination compounds has been investigated by X-ray absorption spectroscopy (XAS). The K-pre-edge spectra are interpreted with the aid of time-dependent density functional theory (TD-DFT). This method was calibrated for the prediction of manganese K-pre-edges with different functionals. Moreover the nature of all observed features could be identified and classified according to the corresponding set of acceptor orbitals, either Is to 3d transitions or metal-to-ligand charge transfer (MLCT) bands. The observable MLCT bands are further divided into features that correspond to transitions into empty pi* orbitals of pi-donor ligands and those of pi-acceptor ligands. The ability to computationally reproduce the observed features at the correct relative transition energy is strongly dependent on the nature of the transition. A detailed analysis of the electronic structure of a series of Mn coordination compounds reveals that the different classes of observable transitions provide added insight into metal-ligand bonding interactions.