PHOTOINDUCED ENERGY-TRANSFER AND ELECTRON-TRANSFER PROCESSES IN DINUCLEAR RUTHENIUM(II) AND OR OSMIUM(II) COMPLEXES CONNECTED BY A LINEAR RIGID BIS-CHELATING BRIDGE/

A rigid and linear bridging ligand containing two 4,5-diazafluorene ch elating units separated by an adamantane spacer (diazf-a-diazf) has be en synthesized and its dinuclear complexes [(bpy)(2)Ru(diazf-a-diazf)R u(bpy)(2)](4+) (Ru-II. FAF . Ru-II), [(bpy)(2)Os(diazf-a-diazf)Os(bpy) (2)](4+) (Os-II. FAF . Os-II), and [(bpy)(2)Ru(diazf-a-diazf)Os(bpy)(2 )](4+) (Ru-II. FAF . Os-II) have been prepared as PF6- salts. In these novel compounds, each Ru-based and Os-based unit displays its own abs orption spectrum and electrochemical properties, regardless of the: pr esence of a second metal-based unit. The luminescence properties have also been investigated and it has been shown that electronic energy tr ansfer takes place in the mixed-metal Ru-II. FAF . Os-II species at 77 K from the Ru-based to the Os-based unit with rate constant 2.6 . 10(8 ) s(-1). At room temperature the intrinsic decay of the Ru-based unit is too fast (3.3 . 10(9) s(-1)) to allow the occurrence of energy tran sfer. Partial oxidation of the binuclear compounds Ru-II. FAF . Os-II and Os-II. FAF . Os-II by Ce-IV in acetonitrile-water solutions leads to the mixed-valence Ru-II. FAF . Os-III and Os-II. FAF . Os-III speci es where the oxidized metal-based unit quenches, by electron transfer, the luminescent excited state of the unit that is not oxidized. At ro om temperature, the rate constants for the excited state Ru-II. FAF . Os-III --> Ru-III. FAF . Os-II and Os(II)FAF . Os-III --> Os-III. FA F . Os-II processes are 8.3 . 10(8) s(-1) and 3.9 . 10(8) s(-1), respe ctively, and the rate constant for the back-electron-transfer process Ru-III. FAF . Os-II --> Ru-II. FAF . Os-III is 2.9 . 10(7) s(-1).