CONTROL OF INTRAMOLECULAR ELECTRON-TRANSFER BY A CHEMICAL-REACTION - THE 4,4'-AZOPYRIDINE/1,2-BIS(4-PYRIDYL)HYDRAZINE SYSTEM

The complexation of 4,4'-azopyridine by the pentaammineruthenium(II) group is described. The metal sites are coordinated to the pyridyl nitrogen atoms and interact through the conjugated azo linkage. Upon oxidation, an intervalence absorption is detected, but it is unresolved with respect to the nearby metal-to-ligand charge-transfer band. The acidification of the binuclear pentaammineruthenium(II) complex gives rise to a pH induced intramolecular redox reaction yielding a ruthenium(III) complex of the reduced form of 4,4'-azopyridine, i.e. 1,2-bis(4-pyridyl)hydrazine. Reduction of the latter complex allows the investigation of intervalence transfer through 1,2-bis(4-pyridyl)hydrazine. It is found that the electronic interaction is greatly reduced in the reduced form of the ligand with respect to the oxidized form. This modification is discussed in the frame of an extended Huckel molecular orbital calculation.