Heteroleptic 5, 5'-disubstituted-2, 2'-bipyridine complexes of ruthenium(II): spectral, electrochemical, and structural investigations

摘要

The optical absorption and luminescence spectra, the electrochemical behavior, and the X-ray cryatal strcuture of a series of three heteroleptic Ru(II) complexes in comparion to [Ru(bipy)_3~2+ are reported. The complexes examined are of the type [Ru(bipy)_2 (bipy')] (PF_6)_2 with bipy=2, 2'-bipyridine (6). Absorption bands and redox waves are fully assigned. The positon of bads or half-wave potentials can be correlated with the electron-withdrawing/donating properties of the bipy' ligand. The relative emission intensities of complexes with 4 and 6 can be modulated through the hydrogen-bonding capabilities of the solvent (MeOH and H_2O). The cyclic voltammograms between +1.5 and -2.2 V show a reversible metal-oxidation wave and two to four reduction waves, attributed to successive reductions of the different ligands. Ligand 4 can only be oxidized. Correlations between spectrosocpical and electrochmical data give a linear relation for h#nu#_max~abs, H#nu#_max~em versus (triangle open)E_1/2. A comparison with complexes with the analogous 4, 4'-disubstituted-2. 2'-bipyridine ligands reveaals pronounced differences in the position of the MLCT-absorption and emissin bands due to the 5- or 4-position of the substituent.