X-ray structure and DFT study of neutral mixed phosphine azoimine complexes of ruthenium

Geometry optimization for a cis-[RuII(dppe)LCl2] (1–8) {L = C6H5NNC(COCH3)NAr, Ar = 2,4,6-trimethylphenyl (L1), 2,5-dimethylphenyl (L2), 4-tolyl (L3), phenyl (L4), 4-methoxyphenyl (L5), 4-chlorophenyl (L6), 4-nitrophenyl (L7), 2,5-dichlorophenyl (L8); dppe = Ph2P(CH2)2PPh2} was effected using the gaussian 03 protocol at density functional theory (DFT) B3LYP level with 6-31G∗/lanl2dz mixed basis. In addition, the complex cis-[RuII(dppe)L3Cl2] (3) has been further characterized by X-ray diffraction analysis. It was found that the optimized structure using 6-31G∗/lanl2dz has a large agreement with the X-ray data. DFT calculations show that upon solvation both Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) molecular orbitals are stabilized and their energy gap is increased. TD-DFT calculations show that the intense broad band centered at λmax ∼ 506 nm is assigned to “mixed metal-ligand-to-ligand charge-transfer” (MMLLCT) while the weak low energy band centered on ∼840 nm is assigned to the pure MLCT transition. The low intensity for the low energy MLCT transition can be explained by the large mixing between the azoimine (L) and (Ru(dπ)) orbital.

Geometry optimization for a cis-[RuII(dppe)LCl2] (1–8) {L = C6H5NNC(COCH3)NAr, Ar = 2,4,6-trimethylphenyl (L1), 2,5-dimethylphenyl (L2), 4-tolyl (L3), phenyl (L4), 4-methoxyphenyl (L5), 4-chlorophenyl (L6), 4-nitrophenyl (L7), 2,5-dichlorophenyl (L8); dppe = Ph2P(CH2)2PPh2} was effected using the gaussian 03 protocol at density functional theory (DFT) B3LYP level with 3-21G∗/lanl2dz and 6-31G∗/lanl2dz mixed basis sets. In addition, cis-[RuII(dppe)L3Cl2] has been further characterized by X-ray diffraction analysis. However, it was found that the optimized structure using 6-31G∗/lanl2dz has a large agreement with the X-ray data. Based on DFT calculation shows that upon solvation both Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) molecular orbitals are stabilized and their energy gap is increased. TD-DFT calculations show that the intense broad band centered around λmax ∼ 506 nm is assigned to “mixed metal-ligand-to-ligand charge-transfer” (MMLLCT) while the weak low energy band centered around ∼840 nm is assigned to the pure MLCT transition.Figure optionsDownload as PowerPoint slideHighlights
► DFT calculations using lanL2DZ/6-31G∗ basis set are compared favorably to UV-Vis and E1/2ox experimental data for a series of [Ru(dppe)LCl2] (1–8) complexes.
► DFT method gave structural values relatively in a good agreement with those determined by X-ray diffraction for a representative complex (3) of this family.
► TD-DFT calculations reproduce the experimental absorption spectra very well especially when the polarized continuum model is taken into account.
► The low intensity for the low energy MLCT transition for these complexes can be explained by the large mixing between the azoimine (L) and (Ru(dπ)) orbital.