Electronic excited states of mixed sandwich complexes, (η7-C7H7)(η5-C5H5) M (M = V, Cr): Investigation with time-dependent density functional theory

The nature and energies of the low-lying electronic excited states of vanadium and chromium cycloheptatrienyl cyclopentadienyl complexes are determined on the basis of time-dependent density functional theory (TD DFT) calculations compared with the experimental gas-phase and condensed-phase absorption spectra. Both intravalency and Rydberg electronic excitations are taken into account. It is demonstrated that TD DFT can predict correctly the absorption band positions and describe well the influence of the metal atom and the ligand on the electronic transition energies. On the basis of comparison with the experimental transition energies the best combinations of the functional and basis set are chosen. For the mixed sandwiches, the "pure" BPW91 and hybrid B3LYP functionals are found to perform much better than the range-separated CAM-B3LYP and WB97XD functionals. The TD DFT calculations suggest new assignments for the Rydberg 4d peak in the gas-phase spectrum of the chromium complex and for the long-wavelength absorption band in the solution spectrum of the vanadium derivative.