Cyclometallated Compounds of Ruthenium(ii): Characterization, Photophysical and Electrochemical Properties.
Date of Award
Doctor of Philosophy (PhD)
The first examples of ruthenium mixed ligand complexes of the type Ru(bpy)(,2) L ('+), in which bpy = 2,2'-bipyridine and L = the cyclometallating ligands 2-(3'nitrophenyl)pyridine (1), 2-phenylpyridine (2), benzo h quinoline (3), azobenzene (4), and p-dimethylaminoazobenzene (5), have been prepared and characterized. The first use for this type of compound of two-dimensional homo-nuclear decoupled auto-correlated Fourier transform ('1)H NMR (HDCOSY) spectra, have allowed the assignment of all distinguishable aromatic protons in each compound, and have confirmed the cyclometallation of L. The absorption spectrum of each of the complexes contains several low energy bands which are assigned as metal-to-ligand charge-transfer (MLCT) transitions. The compounds do not emit light following photoexcitation of deaerated acetonitrile solutions at room temperature, but emission of light is observed from EtOH/MeOH (4:1) glasses of the compounds with L = 1, 2 and 3 at 77K. These results and some calculations on the ligands, at the CNDO level of approximation, lead to the assignment of the lowest energy MLCT band as (pi)*(bpy) (<---) d(pi)(Ru) for L = 1, 2 and 3 and as (pi)* (L) (<---) d(pi)(Ru) for L = 4 and 5. The major perturbations resulting from cyclometallation are an increase in electron density around the metal atom and an increase in the crystal field strength. These changes are reflected in the electrochemical behavior of the complexes that is shown in the cyclic voltammetry experiments as well as in their spectroscopic behavior that is shown in the absorption, emission, and photochemical experiments. These results are contrasted with those of the diimine ruthenium analogues. An X-ray crystal structure determination of Ru(bpy)(,2) 1 ('+) has revealed a shorter (by 0.18 (ANGSTROM)) than single bond Ru-C distance (1.997 (7)), suggesting substantial multiple bonding (M (--->) L). The Ru-N bond trans to the Ru-C bond is longer than the other Ru-N bonds by 0.05-0.10 (ANGSTROM), as expected from the trans influence of the strong field carbanion ligand.
Reveco, Patricio Gabriel, "Cyclometallated Compounds of Ruthenium(ii): Characterization, Photophysical and Electrochemical Properties." (1985). LSU Historical Dissertations and Theses. 4073.