H_2O-DMF混合溶剂中[Co(N_3)(NH_3)_5]^(2+)与[Fe(H_2O)_6]^(2+)间电子转移反应

ELECTRON TRANSFER REACTION OF [Co(N_3)(NH_3)_5]^(2+) BY IRON(Ⅱ) IN WATER MIXED WITH N,N-DIMETHYLFORMAMIDE

研究了H_2O-DMF馄合溶剂中[Co(N_3)(NH_3)_5]^(2+)被Fe(Ⅱ)还原的反应速度变化规律后,证实:当DMF的摩尔分数X_(DMF)<0.3时,表观速度常数K_(aDD)随着X_(DMF)增大而增大;X_(DMF)>0.3时,K_(app)随着X_(DMF)增大而减小;K_(aDD)与[H^+]有良好线性关系。 H_2O-DMF混合溶剂中所测定的吸收光谱显示出:近紫外区溶液的吸光度随X_(DMF)增大而增大,它反映出Fe(Ⅱ)的配位圈中配体H_2O分子被DMF分子逐渐置换而形成混合配体配合物的过程。 还观察到,在H_2O-DMF混合溶剂中,Fe(Ⅱ)的电极电势与X_(DMF)的依存性:随X_(DMF)增加,Fe(Ⅱ)的电极电势下降,但X_(DMF)>0.3后,Fe(Ⅱ)的电极电势几乎为一定值。 因此,反应速度的变化,可归因于Fe(Ⅱ)配位圈中水分子的被置换和Fe(Ⅱ)电极电势的变化上。

The kinetics of the reduction of the [Co(N3))(NH3)5] 2+ by iron(Ⅱ) was investigated in mixed solvents of N,N-Dimethylformamide and water. The apparent rate constant, kapp substantially increases with an increase in the dimethylfor amide concentration range XDMF <0.3,but it decreases as XDMF mol fraction higher than app is also dependent upon [H + ]and in a linear relationship with [H + ]. The absorption spectra of iron(Ⅱ) in mixed solvents of imethylformamide and water has been determined .The absorbances of the solutions in the near-ultraviolet region increase with an increase of DMF to an aqueous solution of iron(Ⅱ).This seems to suggest that some of the water molecules in the coordination-sphere of the iron(Ⅱ) are replaced by dimethylformaide molecules,a mixed-ligand complex such as [Fe(H2O)6_n(DMF)m]2+ is formed. The dependence of the dimethylformamide concentration on the electrode potential of iron (Ⅱ) was also examined in the course of this work .The electrode potential of iron(Ⅱ) decreases with an increase in the mol fraction of dimethylformamide, but the solvent composition when ranged at XDMF >0.3, seems to be almost constant. It follows that the acceleration of the reaction rate is due to the addition of dimethylformamide solvent and related to the change in electrode potential of iron(Ⅱ)ion.