Busby Michael, Matousek Pavel, Towrie Michael, Clark Ian P, Motevalli Majid, Hartl Frantisek, Vlcek Antonín
Department of Chemistry and Centre for Materials Research, Queen Mary, University of London, Mile End Road, London E1 4NS, United Kingdom.
Inorg Chem. 2004 Jul 12;43(14):4523-30. doi: 10.1021/ic049659m.
The lowest allowed electronic transition of fac-[Re(Cl)(CO)(3)(bopy)(2)] (bopy = 4-benzoylpyridine) has a Re --> bopy MLCT character, as revealed by UV-vis and stationary resonance Raman spectroscopy. Accordingly, the lowest-lying, long-lived, excited state is Re --> bopy (3)MLCT. Electronic depopulation of the Re(CO)(3) unit and population of a bopy pi orbital upon excitation are evident by the upward shift of nu(CO) vibrations and a downward shift of the ketone nu(C=O) vibration, respectively, seen in picosecond time-resolved IR spectra. Moreover, reduction of a single bopy ligand in the (3)MLCT excited state is indicated by time-resolved visible and resonance Raman (TR(3)) spectra that show features typical of bopy(*)(-). In contrast, the lowest allowed electronic transition and lowest-lying excited state of a new complex fac-Re(bopy)(CO)(3)(bpy) (bpy = 2,2'-bipyridine) have been identified as Re --> bpy MLCT with no involvement of the bopy ligand, despite the fact that the first reduction of this complex is bopy-localized, as was proven spectroelectrochemically. This is a rare case in which the localizations of the lowest MLCT excitation and the first reduction are different. (3)MLCT excited states of both fac-[Re(Cl)(CO)(3)(bopy)(2)] and fac-Re(bopy)(CO)(3)(bpy) are initially formed vibrationally hot. Their relaxation is manifested by picosecond dynamic shifts of nu(C(triple bond)O) IR bands. The X-ray structure of fac-[Re(bopy)(CO)(3)(bpy)]PF(6).CH(3)CN has been determined.
紫外可见光谱和稳态共振拉曼光谱表明,面式-[Re(Cl)(CO)₃(bopy)₂](bopy = 4-苯甲酰基吡啶)允许的最低电子跃迁具有Re→bopy MLCT特征。因此,最低能量、长寿命的激发态是Re→bopy (³)MLCT。在皮秒时间分辨红外光谱中,分别观察到ν(CO)振动的向上位移和酮ν(C=O)振动的向下位移,这表明激发时Re(CO)₃单元的电子去填充和bopy π轨道的填充。此外,(³)MLCT激发态中单个bopy配体的还原由时间分辨可见光谱和共振拉曼(TR³)光谱表明,这些光谱显示出bopy⁻*的典型特征。相比之下,新配合物面式-[Re(bopy)(CO)₃(bpy)]⁺(bopy = 2,2'-联吡啶)允许的最低电子跃迁和最低能量激发态已被确定为Re→bopy MLCT,且不涉及bopy配体,尽管该配合物的首次还原是bopy局域化的,这已通过光谱电化学方法得到证实。这是一个罕见的情况,其中最低MLCT激发和首次还原的局域化不同。面式-[Re(Cl)(CO)₃(bopy)₂]和面式-[Re(bopy)(CO)₃(bpy)]⁺的(³)MLCT激发态最初都是振动热形成的。它们的弛豫表现为ν(C≡O)红外带的皮秒动态位移。已确定面式-[Re(bopy)(CO)₃(bpy)]PF₆·CH₃CN的X射线结构。