(8-Amino)quinoline and (4-Amino)phenanthridine Complexes of Re(CO)₃ Halides

Area of Science:

• Organometallic Chemistry
• Photophysics
• Computational Chemistry

Background:

• Rhenium tricarbonyl complexes are valuable in photophysical studies.
• Amino-substituted heterocycles offer tunable electronic properties for ligand design.

Purpose of the Study:

• To synthesize and characterize novel rhenium (Re(CO)3X) complexes featuring (8-amino)quinoline and (4-amino)phenanthridine ligands.
• To investigate the structural, electronic, and photophysical properties of these complexes.
• To elucidate the role of ligand structure and computational methods in understanding their electronic transitions.

Main Methods:

• Synthesis of Re(CO)3X complexes with bidentate (amino)heterocyclic ligands.
• X-ray crystallography for structural determination.
• UV-visible absorption spectroscopy for electronic characterization.
• Density Functional Theory (DFT) and Time-Dependent DFT (TDDFT) calculations, including spin-orbit coupling (SOC).

Main Results:

• The (amino)heterocycles bind as bidentate ligands with symmetric Re-N bonds.
• Structural variations between (8-amino)quinoline and (4-amino)phenanthridine complexes were minimal.
• UV-visible spectra were similar, with expanded π-systems in phenanthridines increasing transition intensity.
• Computational modeling indicated MLCT character for phenanthridine complexes and mixed π-π*/MLCT for quinoline complexes.
• Spin-orbit coupling was essential for accurately modeling electronic absorption spectra.

Conclusions:

• The electronic properties of Re(CO)3X complexes are influenced by the π-system expansion of the heterocyclic ligand.
• Accurate modeling of electronic absorption spectra necessitates the inclusion of spin-orbit coupling in TDDFT calculations.
• These findings provide insights into ligand design for tuning the photophysical properties of rhenium complexes.