Transition metal complexes excited-state geometries

The geometry changes which transition metal complexes undergo when excited electronic states are populated are determined by using a combination of electronic emission and absorption spectroscopy, pre-resonance Raman spectroscopy, excited state Raman spectroscopy, and time-dependent theory of molecular spectroscopy. 

Undoubtedly, the most general conclusion to be drawn from this overview of recent TDDFT calculations on transition-metal complexes is that this technique, compared to other available theoretical methods, provides state-of-the-art results for excitation energies. We stress that in order for this to be a valid statement, there are two points that should receive due attention the applied functional, and the geometry of the system. 

Semiempirical methods have played and still play the major role in the elucidation of chemical bonding, the calculation of molecular geometries, and for the determination of other properties of larger molecules and extended systems. While ab-initio calculations have supplemented them for small and, increasingly, for medium-sized molecules, semiempirical methods still remain the better alternative even for relatively small molecules, when information on excited electronic states is demanded. This holds for open shell systems such as transition metal complexes, and, in particular, when heavier atoms are involved and/or spin-orbit coupling has to be considered. 

---