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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Kinetics and Equilibria of the Interaction of Indium(III) with Pyrocathecol Violet by Relaxation Spectrometry
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Kinetics and Equilibria of the Interaction of Indium(III) with Pyrocathecol Violet by Relaxation Spectrometry

机译：弛豫光谱法研究铟（III）与吡咯烷醇紫的相互作用的动力学和平衡

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摘要

A temperature-jump apparatus with laser light sources was used to investigate the binding mechanism of indium(III) to pyrocathecol violet (3,3',4'-trihydroxyfuchsone-2-sulfonic acid, whose neutral form is denoted as H_4L). Spectrophotometric measurements revealed that for [H~+]>0.015 M, the main bound species are MH_3L~2+ and MH_2L~+ whereas for [H~+]<0.015 M, the main bound species is M_2L~2+. Two relaxation effects were observed. The fast relaxation is associated mainly with the reaction steps M~3++H_3L~-<->MH_3L~2+(k_2=1.2×10~6 M~(-1) s~(-1), k_(-2)=1.5×10~5 s~(-1)) and MOH~(2+)+H_3L~-<->MH_2L~+(k_3=4.4×10~7 M~(-1) s~(-1), k_(-3)=7.4×10~2 s~(-1)). The rate constant k_2 decreases, whereas k_(-2) increases, with increasing ionic strength. Addition of Na_2SO_4 results in a large reduction of the fast relaxation time that is ascribed to the binding of indium(III) to sulfate. Analysis of the relaxation time dependence on the sulfate concentration provides the binding constant of the indium-sulfate complex (K=1.5×10~2 M~(-1)). The activation parameters for the step M~(3+)+H_3L~-<->MH_3L~(2+) were obtained as (triangle open)H_1f~++=25.3 kJ mol~(-1), (triangle open)S_1f~++=-6.2 J mol~(-1) K~(-1), (triangle open)H_1d~++=13.4 kJ mol~(-1), (triangle open)S_1d~++=-57 mol~(-1) K~(-1). The enthalpy change of the just described reaction step was measured by spectrophotometry at different temperatures and by the relaxation amplitudes, the average value being (triangle open)H_1~0=11.9 kJ mol~(-1). The slow effect is associated with a complexation path leading to formation of M_2L~+. The amplitude analysis of the slow relaxation gives (triangle open)H_2~0=7.6 kJ mol~(-1). A comparison of this work with other studies on complexation with indium(III) suggests that In(OH~(2+) reacts according to the I_d mechanism, whereas the mode of activation of In(H_2O)_6~3+ seems to be less definite because a clear indication about the dependence (or independence) of the rates on the lignad basicity does not emerge. This observation and the slightly negative value of (triangle open)S_1f~++ hints at the possibility that indium(III) undergoes complexation by a concerted mechanism.
机译：使用带有激光源的温度跳跃仪研究铟（III）与邻苯二酚紫（3,3'，4'-三羟基紫红色-2-磺酸，其中性形式表示为H_4L）的结合机理。分光光度法测量结果表明，对于[H〜+]> 0.015 M，主要结合物为MH_3L〜2 +和MH_2L〜+，而对于[H〜+] <0.015 M，主要结合物为M_2L〜2 +。观察到两种松弛效果。快速弛豫主要与反应步骤M〜3 ++ H_3L〜--MH_3L〜2 +（k_2 = 1.2×10〜6 M〜（-1）s〜（-1），k _（-2 ）= 1.5×10〜5 s〜（-1））和MOH〜（2 +）+ H_3L〜-<-> MH_2L〜+（k_3 = 4.4×10〜7 M〜（-1）s〜（-1） ），k _（-3）= 7.4×10〜2 s〜（-1））。随着离子强度的增加，速率常数k_2减小，而k _（-2）增大。 Na 2 SO 4的加入导致快速弛豫时间大大减少，这归因于铟（III）与硫酸盐的结合。分析弛豫时间对硫酸盐浓度的依赖性，提供了硫酸铟络合物的结合常数（K = 1.5×10〜2 M〜（-1））。步骤M〜（3 +）+ H_3L〜-→-MH_3L〜（2+）的激活参数为（三角形开度）H_1f〜++ = 25.3 kJ mol〜（-1），（三角形开度） S_1f〜++ =-6.2 J mol〜（-1）K〜（-1），（三角形开放）H_1d〜++ = 13.4 kJ mol〜（-1），（三角形开放）S_1d〜++ =-57摩尔〜（-1）K〜（-1）。通过分光光度法在不同温度和弛豫幅度下测量刚刚描述的反应步骤的焓变化，平均值为（三角形开口）H_1〜0 = 11.9 kJ mol〜（-1）。缓慢的作用与导致M_2L〜+形成的络合路径有关。缓慢弛豫的振幅分析给出了（三角形开放）H_2〜0 = 7.6 kJ mol〜（-1）。这项工作与其他有关与铟（III）络合的研究的比较表明，In（OH〜（2+）根据I_d机制反应，而In（H_2O）_6〜3 +的激活方式似乎较少之所以确定，是因为没有明确表明速率对直链碱度的依赖性（或独立性），这一观察结果和（三角形开口的）S_1f〜++的负值暗示了铟（III）可能发生络合通过协调机制。

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