Anbalagan K, Lydia I Sharmila
Department of Chemistry, Pondicherry University, Kalapet, Puducherry 605014, India.
Spectrochim Acta A Mol Biomol Spectrosc. 2008 Mar;69(3):964-70. doi: 10.1016/j.saa.2007.05.064. Epub 2007 Jun 23.
The effect of solvent participation on the ligand-to-metal charge transfer (LMCT, L-->Co(III)) reduction of the of Co(III)(en)(2)Br(RC(6)H(4)NH(2))(2+) where R=m-OCH(3), p-F, H, m-CH(3), p-CH(3,)p-OC(2)H(5) and p-OCH(3) were examined in aqueous 2-methyl-2-propanol (Bu(t)OH) solutions. The change in the reduction behavior of Co(III) centre was also examined through cyclic voltammetric studies. The observed reduction in quantum yield due to LMCT excitation can mainly be accounted using linear solvation energy relationship (LSER) comprising model correlation equations. These consist of empirical parameters such as Grunwald-Winstein's solvent ionizing power, Y, Dimroth-Richardt's solvent micro-polarity parameter, E(T)(N), Gutmann's donor number, DN(N), along with Kamlet-Taft's solvatochromic parameters (hydrogen bond acceptor acidity/basicity alpha/beta and solvent dipolarity/polarizability, pi*). The origin of solvent effect is found to be due to microscopic interaction between the solvent donor and the nitrogen-bound hydrogen of the ligand. Cyclic voltammograms show an irreversible reduction of Co(III) in DMF using Glassy Carbon Electrode, GCE, the redox peaks for the aniline complexes appear at -0.20 and 0.525V. Irradiation of the complexes with UV light (lambda=254nm) in binary mixtures produce Co(II)(aq) and the concentration of this species are highly dependent on x(alc) (x(alc)=mole fraction of alcohol). The observed quantum yield (logPhi(Co(II))) is found to be linearly related to mole fraction of organic co-solvent added in the mixture, therefore, logPhi(Co(II))=26.41 x 10(-2) when x(2)=0.0094 and 43.75 x 10(-2) when x(2)=0.076 for a typical complex Co(III)(en)(2)Br(p-OCH(3)C(6)H(4)NH(2))(2+) in aqueous 2-methyl-2-propanol at 300K. Cyclic voltammetry and LSER analyses illustrate the variation of reduction property of Co(III) by the aryl ligand and homogeneous solvation of the excited state of the complex Co(III)(en)(2)Br(RC(6)H(4)NH(2))(2+) in H(2)O/Bu(t)OH mixtures.
研究了在2-甲基-2-丙醇（叔丁醇）水溶液中，溶剂参与对Co(III)(en)(2)Br(RC(6)H(4)NH(2))(2+)（其中R = 间甲氧基、对氟、氢、间甲基、对甲基、对乙氧基和对甲氧基）的配体到金属电荷转移（LMCT，L→Co(III)）还原的影响。还通过循环伏安法研究了Co(III)中心还原行为的变化。由于LMCT激发导致的量子产率降低主要可以用包含模型相关方程的线性溶剂化能关系（LSER）来解释。这些方程由诸如Grunwald-Winstein溶剂离解能力Y、Dimroth-Richardt溶剂微极性参数E(T)(N)、Gutmann给体数DN(N)以及Kamlet-Taft溶剂显色参数（氢键受体酸度/碱度α/β和溶剂偶极矩/极化率π*）等经验参数组成。发现溶剂效应的起源是由于溶剂给体与配体中氮结合氢之间的微观相互作用。循环伏安图显示在二甲基甲酰胺（DMF）中使用玻碳电极（GCE）时Co(III)的不可逆还原，苯胺配合物的氧化还原峰出现在-0.20和0.525V。在二元混合物中用紫外光（λ = 254nm）照射配合物会产生Co(II)(aq)，该物种的浓度高度依赖于x(alc)（x(alc)=醇的摩尔分数）。观察到的量子产率（logPhi(Co(II))）与混合物中添加的有机共溶剂的摩尔分数呈线性关系，因此，对于在300K的2-甲基-2-丙醇水溶液中的典型配合物Co(III)(en)(2)Br(p-OCH(3)C(6)H(4)NH(2))(2+)，当x(2)=0.0094时logPhi(Co(II)) = 26.41×10^(-2)，当x(2)=0.076时logPhi(Co(II)) = 43.75×10^(-2)。循环伏安法和LSER分析说明了芳基配体对Co(III)还原性质的影响以及配合物Co(III)(en)(2)Br(RC(6)H(4)NH(2))(2+)在H(2)O/叔丁醇混合物中激发态的均匀溶剂化作用。
