Synthteses, spectroscopic and electrochemical properties of new dinuclear asymmetric and mixed-valent ruthenium complexes

KATZ, NÉSTOR E.; FAGALDE, FLORENCIA; GARCÍA POSSE, MÓNICA E.; VERGARA, MÓNICA M.; ROMERO, ISABEL; LLOBET, ANTONI

Mérida, México

Congreso; XXXVI International Conference on Coordination Chemistry; 2004

ICCC

New  dinuclear asymmetric ruthenium complexes of formula [(tpm)(bpy)Ru(L)Ru(NH3)5](PF6)4, with tpm= tris(1-pyrazolyl)methane, bpy= 2,2?-bipyridine, L = pz (pyrazine), 4,4?-bpy (4,4?-bipyridine) and BPE (trans-1,2-bis(4-pyridil)ethylene), have been prepared and characterized by spectroscopic and electrochemical techniques. Their IR spectra indicate oxidation states (II) for all ruthenium atoms bonded to ammines (= Rua). The redox potentials for the RubIII/RubII couples (Rub = Ru bonded to bpy) incresase in the order BPE < 4,4?-bpy < pz , evidencing the increasing order of p- backbonding effects from Rub to the ligands. Two intense absorption bands have been observed for the three species in the visible region, which can be assigned to metal-to-ligand charge transfer transitions RubII ® bpy and RuaII ® L. These latter bands ?of lower energy- disappear when oxidizing Rua with Br2 in CH3CN to give the mixed-valent localized species [(tpm)(bpy)RubII(L)RuaIII(NH3)5]5+. The metal-to-metal charge transfer transitions RubII ® RuaIII have been detected for all complexes between 600 and 900 nm in CH3CN; from a Marcus-Hush analysis of the experimental data, the distance dependence of the reorganization energy for the intramolecular electron transfer (through the bridgind ligand L) and of the electronic coupling element (between both metal centers) could be assessed.