de Aguiar Inara, Inglez Simone D, Lima Francisco C A, Daniel Juliana F S, McGarvey Bruce R, Tedesco Antônio C, Carlos Rose M
Departamento de Química, Universidade Federal de São Carlos, CP 676, 13565-905, São Carlos, SP, Brasil.
Inorg Chem. 2008 Dec 15;47(24):11519-26. doi: 10.1021/ic8002004.
The electronic absorption spectrum of fac-Mn(CO)(3)(phen)imH, fac-1 in CH(2)Cl(2) is characterized by a strong absorption band at 378 nm (epsilon(max) = 3200 mol(-1) L cm(-1)). On the basis of quantum mechanical calculations, the visible absorption band has been assigned to ligand-to-ligand charge-transfer (LLCT, im-->phen) and metal-to-ligand charge-transfer (MLCT, Mn-->phen) charge transfer transition. When fac-1 in CH(2)Cl(2) is irradiated with 350 nm continuous light, the absorption features are gradually shifted to represent those of the meridional complex mer-Mn(CO)(3)(phen)imH, mer-1 (lambda(max) = 556 nm). The net photoreaction under these conditions is a photoisomerization, although, the presence of the long-lived radical species was also detected by (1)H NMR and FTIR spectroscopy. 355 nm continuous photolysis of fac-1 in CH(3)CN solution also gives the long-lived intermediate which is readily trapped by metylviologen (MV(2+)) giving rise to the formation of the one-electron reduced methyl viologen (MV(*+)). The UV-vis spectra monitored during the slow (45 min) thermal back reaction exhibited isosbestic conversion at 426 nm. On the basis of spectroscopic techniques and quantum mechanical calculations, the role of the radicals produced is analyzed.
面式-[Mn(CO)₃(phen)imH]⁺（面式-1）在二氯甲烷中的电子吸收光谱的特征是在378 nm处有一个强吸收带（εmax = 3200 mol⁻¹ L cm⁻¹）。基于量子力学计算，可见吸收带已被归属为配体到配体的电荷转移（LLCT，im→phen）和金属到配体的电荷转移（MLCT，Mn→phen）电荷转移跃迁。当用350 nm连续光照射二氯甲烷中的面式-1时，吸收特征逐渐发生变化，呈现出经式配合物经式-[Mn(CO)₃(phen)imH]⁺（经式-1，λmax = 556 nm）的吸收特征。在这些条件下的净光反应是光异构化，不过，通过¹H NMR和FTIR光谱也检测到了长寿命自由基物种的存在。在乙腈溶液中用355 nm连续光解面式-1也会产生长寿命中间体，该中间体很容易被甲基紫精（MV²⁺）捕获，从而导致单电子还原的甲基紫精（MV⁺）的形成。在缓慢的（45分钟）热逆反应过程中监测的紫外可见光谱在426 nm处呈现等吸收点转换。基于光谱技术和量子力学计算，分析了所产生自由基的作用。
