Description of excited states in [Re(Imidazole)(CO)₃(Phen)]⁺ including solvent and spin‐orbit coupling effects: Density functional theory versus multiconfigurational wavefunction approach

Abstract

The low-lying electronic excited states of [Re(imidazole)(CO)3 (phen)](+) (phen = 1,10-phenanthroline) ranging between 420 nm and 330 nm have been calculated by means of relativistic spin-orbit time-dependent density functional theory (TD-DFT) and wavefunction approaches (state-average-CASSCF/CASPT2). A direct comparison between the theoretical absorption spectra obtained with different methods including SOC and solvent corrections for water points to the difficulties at describing on the same footing the bands generated by metal-to-ligand charge transfer (MLCT), intraligand (IL) transition, and ligand-to-Ligand- charge transfer (LLCT). While TD-DFT and three-roots-state-average CASSCF (10,10) reproduce rather well the lowest broad MLCT band observed in the experimental spectrum between 420 nm and 330 nm, more flexible wavefunctions enlarged either by the number of roots or by the number of active orbitals and electrons destabilize the MLCT states by introducing IL and LLCT character in the lowest part of the absorption spectrum. © 2016 Wiley Periodicals, Inc.

Excited‐State Reactivity of [Mn(im)(CO)3(phen)]+: A Structural Exploration

“…). Note that a proper comparison with the experimental spectrum can only be achieved when several conformers of the complex are considered . As expected from the molecular orbital picture (see previous section), both complexes present very similar features.…”

“…The frontier ground state Kohn–Sham orbitals of [Mn(im)(CO) 3 (phen)] + shown in Scheme are equivalent to the ones of [Re(im)(CO) 3 (phen)] + discussed in previous work . No significant differences are observed in the shape and energy of the lowest empty and highest occupied molecular orbitals of the Mn complex with respect to the Re.…”

“…The optimized geometry of [Re(im)(CO) 3 (phen)] + in the S 0 electronic ground state for its C S conformer is presented in previous work . When substituting the metal ion with Mn, the minimum energy structure of the S 0 ground state of [Mn(im)(CO) 3 (phen)] + is not significantly modified but only small deviations in the bond distances and angles are obtained.…”

“…The TD‐DFT/TDA calculated absorption spectra of [Re(im)(CO) 3 (phen)] + in water has been previously discussed . The absorption spectra of [Mn(im)(CO) 3 (phen)] + computed under the same conditions is presented here in Figure together with the one of [Re(im)(CO) 3 (phen)] + for comparison.…”

“…Notably, these peaks move to 368, 352, and 333 nm when computed in dichloromethane. The full TD‐DFT/TDA data including the vertical transition energies of the low‐lying singlet and triplets, wavelengths of absorption, oscillator strengths, and most important one‐electron excitations of [Mn(im)(CO) 3 (phen)] + in water are collected in Supporting Information Table S1, together with the data of [Re(im)(CO) 3 (phen)] + for comparison . A careful analysis of the excited states composition indicates that the same one‐electron excitations characterize the absorbing peaks in both complexes.…”