Ru(II) Chloro-Bis(bipyridyl) Complexes with Substituted Pyridine Ligands: Interpretation of Their Electronic Absorption Spectra

A number of complexes were synthesized with the general formula cis-[Ru(Bipy)₂(L)(Cl)](BF₄), where Bipy is 2,2"-bipyridine, L is pyridyne (Py), 4-aminopyridine (4-NH₂py), 4-picoline (4-Mepy), nicotin-amide (3-CONH₂py), isonicotinamide (4-CONH₂py), 3- and 4-cyanopyridine (3-CNpy, 4-CNpy), 4,4"-bipyridine (4,4"-Bipy), trans-1,2-bis(4-pyridyl)ethylene (Bpe), 4,4"-azopyridine (Azpy), pyrazine (Pyz), imidazole (Imid), and NH₃. The semiempirical CINDO-CI method was used to calculate the energies and intensities of transitions in the electronic absorption spectra. The differences observed in the spectra of these compounds are mainly due to the positions of the charge-transfer transitions d(Ru) *(L). Depending on the positions of these transitions, ligands L can be divided into three groups: 1) transitions Ru L lie in the region of the first long-wavelength band d(Ru) *(Bipy) (L = Azpy, Pyz); 2) transitions Ru L lie between the first and second bands due to the charge transfer to Bipy (L = 3-CONH₂py, 4-CONH₂py, 4,4"-Bipy, Bpe, 4-CNpy), and 3) transitions Ru L lie in the region of the second band d(Ru) *(Bipy) (L = Py, 4-Mepy, 3-CNPy, 4-NH₂py, Imid).