Here we report relativistic electronic structure calculations employing all-electron density functional theory (DFT) including scalar and spin-orbit interaction, on the multimetallic sandwich compound [Pd3(C 7H7)2X3]1- (X = Cl - (1), Br- (2), and I- (3)), which can be considered as a [Pd3X3]3- fragment flanked by two ring-ligands [(C7H7)2] 2+. The calculations suggest that the [Pd3X3]3--ligand interaction is mainly arising from electrostatic contributions, where the formally zerovalent Pd atoms allows backdonation of charge from the halide X1- atoms to the [(C7H7)2] 2+ ligands, resulting in a net charge of about +0.4 for each Pd atoms that decreases from 1 to 3. The electronic delocalization estimated via the NICS indexes and the ELF function allows us to describe a significant stabilizing ∑-aromaticity at the center of the Pd3 triangle, which decreases from [Pd3Cl3]3- to [Pd 3I3]3- (1 to 3) due to the softer character of the iodine counterpart, that donates extra charge to the ligands. The calculated electronic transitions via TD-DFT are in reasonable agreement with the experimental data obtained in CH2Cl2 solution, indicating that the most intense transition involves a core-centered [Pd3X 3]3 transition toward the [(C7H 7)2]2+ ligands, with mainly X1- character in the former molecular spinor that is responsible for the variation of the observed λmax according to the variation of X 1-.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry