An introduction to X-ray absorption spectroscopy and its in situ application to organometallic compounds and homogeneous catalysts

This is a short introduction of X-ray absorption spectroscopy (XAS) and its application to homogeneous transition metal compounds and catalysts. An XAS spectrum is composed of two regions, XANES and EXAFS, which provide element-specific information on formal oxidation state and local coordination environment, respectively. For molecules with similar environments, such as a common ligand set, the energy of the absorption edge can be calibrated from standards to obtain the formal oxidation state of unknown compounds. For structurally complex coordination environments, simulated EXAFS spectra obtained from XRD or DFT-modeled structures can be used to ascertain local structural information from an experimental EXAFS spectrum. With fast data acquisition at modern synchrotrons, it is also possible to follow the kinetic transformation of homogeneous compounds under realistic reaction conditions while gaining insight into the structural and electronic changes happening at the metal atom.