| Popis: |
Electron transfer reactions involving the 1,8-bis- (2-pyridyl)-3,6-dithiaoctane copper(II) complex, Cu- (pdto) 2+ , and a series of Ru(II) ammine and bipyridyl complexes have been studied kinetically in MES buffered 0.10 M LiCF 3 CO 2 . Values of the second- order rate constant, k 2 (M -1 s -1 ) are Ru(NH 3 )5 py 2+ , 3.8 × 10 4 ; Ru(NH 3 ) 5 isn 2+ , 1.4 × 10 4 ; Ru(NH 3 ) 4 - bpy 2+ , 2.0 × 10 3 ; cis -Ru(NH 3 ) 4 (isn) 2 2+ , 2.3 × 10 2 ; cis - Ru(bpy) 2 Cl 2 , 4.4 × 10 4 ; Ru(bpy) 2 C 2 O 4 , 4.5 × 10 5 ; at 25.0 °C in 50% aqueous methanol. Data for the ammine complexes, which follow a linear free energy relationship between log k 2 and E°, the Ru(III)/ Ru(II) reduction potential, suggest an outer-sphere mechanism. Inner-sphere electron transfer is indicated with Ru(bpy) 2 Cl 2 and Ru(bpy) 2 C 2 O 4 as reductants. Oxidation of coordinated oxalate occurs with Ru(bpy) 2 C 2 O 4 . The rate constant has also been determined for the oxidation of the 1,8-bis(2-pyridyl)- 3,6-dimethyl-3,6-diazaoctane copper(I) complex, Cu(pdao) + by Ru(NH 3 ) 5 py 3+ in 100% aqueous 0.10 M LiCF 3 CO 2 . A value of 1.8 × 10 4 M -1 s -1 was obtained at 25.0 °C and pH 6.1. Application of the Marcus relations has yielded estimated self-exchange electron-transfer rate constants of 0.63 and 8.1 M -1 s -1 for the Cu(pdto) 2+/+ and Cu(pdao) 2+/+ couples. |
