Venturi Margherita, Marchioni Filippo, Ferrer Ribera Belén, Balzani Vincenzo, Opris Dorina M, Schlüter A Dieter
Università di Bologna, Dipartimento di Chimica G. Ciamician via Selmi 2, I-40126 Bologna, Italy.
Chemphyschem. 2006 Jan 16;7(1):229-39. doi: 10.1002/cphc.200500323.
The PF6- salt of the dinuclear [(bpy)2Ru(1)Os(bpy)2]4+ complex, where 1 is a phenylacetylene macrocycle which incorporates two 2,2'-bipyridine (bpy) chelating units in opposite sites of its shape-persistent structure, was prepared. In acetonitrile solution, the Ru- and Os-based units display their characteristic absorption spectra and electrochemical properties as in the parent homodinuclear compounds. The luminescence spectrum, however, shows that the emission band of the Ru(II) unit is almost completely quenched with concomitant sensitization of the emission of the Os(II) unit. Electronic energy transfer from the Ru(II) to the Os(II) unit takes place by two distinct processes (k(en) = 2.0x10(8) and 2.2x10(7) s(-1) at 298 K). Oxidation of the Os(II) unit of [(bpy)2Ru(1)Os(bpy)2]4+ by Ce(IV) or nitric acid leads quantitatively to the [(bpy)2Ru(II)(1)Os(III)(bpy)2]5+ complex which exhibits a bpy-to-Os(III) charge-transfer band at 720 nm (epsilon(max) = 250 M(-1) cm(-1)). Light excitation of the Ru(II) unit of [(bpy)2Ru(II)(1)Os(III)(bpy)2]5+ is followed by electron transfer from the Ru(II) to the Os(III) unit (k(el,f) = 1.6x10(8) and 2.7x10(7) s(-1)), resulting in the transient formation of the [(bpy)2Ru(III)(1)Os(II)(bpy)2]5+ complex. The latter species relaxes to the [(bpy)2Ru(II)(1)Os(III)(bpy)2]5+ one by back electron transfer (k(el,b) = 9.1x10(7) and 1.2x10(7) s(-1)). The biexponential decays of the [(bpy)2Ru(II)(1)Os(II)(bpy)2]4+, [(bpy)2Ru(II)(1)Os(III)(bpy)2]5+, and [(bpy)2Ru(III)(1)Os(II)(bpy)2]5+ species are related to the presence of two conformers, as expected because of the steric hindrance between hydrogen atoms of the pyridine and phenyl rings. Comparison of the results obtained with those previously reported for other Ru-Os polypyridine complexes shows that the macrocyclic ligand 1 is a relatively poor conducting bridge.
制备了双核[(bpy)₂Ru(1)Os(bpy)₂]⁴⁺配合物的PF₆⁻盐，其中1是一个苯乙炔大环，在其形状持久结构的相对位置包含两个2,2'-联吡啶（bpy）螯合单元。在乙腈溶液中，基于Ru和Os的单元表现出与母体同双核化合物中相同的特征吸收光谱和电化学性质。然而，发光光谱表明Ru(II)单元的发射带几乎完全猝灭，同时Os(II)单元的发射被敏化。从Ru(II)到Os(II)单元的电子能量转移通过两个不同的过程发生（在298 K时k(en) = 2.0×10⁸和2.2×10⁷ s⁻¹）。[(bpy)₂Ru(1)Os(bpy)₂]⁴⁺的Os(II)单元被Ce(IV)或硝酸氧化定量地生成[(bpy)₂Ru(II)(1)Os(III)(bpy)₂]⁵⁺配合物，其在720 nm处表现出bpy到Os(III)的电荷转移带（ε(max) = 250 M⁻¹ cm⁻¹）。[(bpy)₂Ru(II)(1)Os(III)(bpy)₂]⁵⁺的Ru(II)单元受到光激发后，电子从Ru(II)转移到Os(III)单元（k(el,f) = 1.6×10⁸和2.7×10⁷ s⁻¹），导致瞬态形成[(bpy)₂Ru(III)(1)Os(II)(bpy)₂]⁵⁺配合物。后者通过反向电子转移（k(el,b) = 9.1×10⁷和1.2×10⁷ s⁻¹）弛豫回到[(bpy)₂Ru(II)(1)Os(III)(bpy)₂]⁵⁺。[(bpy)₂Ru(II)(1)Os(II)(bpy)₂]⁴⁺、[(bpy)₂Ru(II)(1)Os(III)(bpy)₂]⁵⁺和[(bpy)₂Ru(III)(1)Os(II)(bpy)₂]⁵⁺物种的双指数衰减与两种构象体的存在有关，正如由于吡啶和苯环氢原子之间的空间位阻所预期的那样。将所得结果与先前报道的其他Ru-Os多吡啶配合物的结果进行比较表明，大环配体1是一个相对较差的导电桥。
