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Structural and Theoretical Study of Some New Rhenium(I) Tricarbonyl Complexes with Non-heterocyclic Diimine Ligands: The Comparison of the σ-Donation and π-accepting Character of the Ligands

Kalaghchi, Azadeh | 2017

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50158 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Kia, Reza
  7. Abstract:
  8. Rhenium(I) tricarbonyl complexes with NN-donor ligands display promising properties for potential applications as molecular catalysts for the reduction of carbon dioxide and as biocompatible pro-drugs for the controlled release of carbon monoxide. In this context the diimine type ligands are one of the most widely used bidentate chelating moieties. In this work, several [Re(CO)3(DAB)X] complexes were prepared in a standard manner by replacement of two cis CO groups in the starting bromo- or chloro-pentacarbonylrhenium complexes with 1,4-diazabutadiene (DAB) ligands. Their pseudo-octahedral facial structures were established using FT-IR, 13C-NMR and 1H-NMR and confirmed by X-ray crystallography. Interest in these compounds is driven by their attractive features, including the ability to tune their photophysical properties by varying the diimine ligand, and the axial ligand (such as the halide). Density functional theory (DFT) was used for geometry optimization of the singlet states in gas phase and the electronic structure calculations. The charge decomposition analyses and molecular orbital studies by AOMix 6.88 software revealed the nature of the composition of the molecular orbitals of the complexes based on the fragments analysis and also charge donation and back-donation character of DAB ligands. Charge decomposition analysis revealed that in all complexes the electron donation of the DAB ligands is significantly greater than the back-donation which is in good agreement to the positive charge carrying on the DAB ligands based on the Mulliken and NPA population analyses. On the other hand, strong π-accepting properties of the three carbonyl groups in the complexes compete with the π-accepting ability of the DAB ligands and the overall result is the significant decreasing of the π-accepting characters of the DAB ligands with respect to the electron donation properties. Details of the singlet excited state character are revealed by TD-DFT calculations, calculated changes of electron density distribution using electron density difference map and confirmed the MLCT, XLCT and IL character of the electronic transitions. Theoretical calculations using AIM showed that the Re−CO bond strength is low in these complexes due to the steric bulk of the diimine ligand around the metal center. These results indicate the possible use of the DAB ligand especially 2,6-ipr2DAB in the synthesis of reactive metal carbonyl complexes with applications as CO releasing molecules (CORMs) or other photoactive materials
  9. Keywords:
  10. X Ray Diffraction ; Density Functional Theory (DFT) ; Time Dependent Density Functional Theory ; Rhenium (I) Tricarbonyl ; Diazabutadienl-1,4 Ligands (DAB)

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