ABSTRACT
In this article, we report the relativistic electronic structure, including spin-orbit interaction, employing all-electron density functional theory calculations on the multimetallic sandwich compound [(CNT)Pd(4)(COT)](1+) (1), which can be considered as a [Pd(4)](2+) fragment flanked by two ring-ligands, namely, cyclononatetraenyl (CNT(1-)) and cyclooctatetraene (COT), as well as the dimer of 1, hereafter 2. The calculations suggest that the Pd(4)-ligand interaction is mainly electrostatic, being the main responsible term for the stabilization of the almost fully occupied 4d shell [Pd(4)](2+) fragment. The ring currents and electronic delocalization estimated via the nuclear independent chemical shifts indices and electron localization function, allow us to describe a significant sigma-aromaticity at the center of the Pd(4) square in 1, which in conjunction with the aromaticity arising from the ligands induce considerable aromatic character inside of the multimetallic metallocene.
ABSTRACT
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 [Pd(3)(C(7)H(7))(2)X(3)](1-) (X = Cl(-) (1), Br(-) (2), and I(-) (3)), which can be considered as a [Pd(3)X(3)](3-) fragment flanked by two ring-ligands [(C(7)H(7))(2)](2+). The calculations suggest that the [Pd(3)X(3)](3-)-ligand interaction is mainly arising from electrostatic contributions, where the formally zerovalent Pd atoms allows backdonation of charge from the halide X(1-) atoms to the [(C(7)H(7))(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 sigma-aromaticity at the center of the Pd(3) triangle, which decreases from [Pd(3)Cl(3)](3-) to [Pd(3)I(3)](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 CH(2)Cl(2) solution, indicating that the most intense transition involves a core-centered [Pd(3)X(3)](3) transition toward the [(C(7)H(7))(2)](2+) ligands, with mainly X(1-) character in the former molecular spinor that is responsible for the variation of the observed lambda(max) according to the variation of X(1-).
