整数斜率点在萃取法测定配合物稳定常数中的应用

The Application of Integer Slope Points in Determination of Stability Constants by Extraction Method

提出了整数斜率点应用于萃取法测定配合物稳定常数的方法,即在金属离子分配比对数值lgD对自由配体浓度负对数pL一阶微分曲线上找出整数斜率点i-c(i=0,1,2,…,n)及其对应的pL值,i为配离子MLi配位数,c为被萃取配离子MLc配位数.在这些pL值分别有lgD=lgλc+(lgβc-lgβi)+(i-c)pL+lgΦMLi,max,式中λc为被萃取配离子在有机相与水相的分配常数,β为配合物累积稳定常数,ΦMLi,max为水相中配离子MLi的最大分布系数.式中略去lgΦMLi,max,当i=c,0时分别得到lgλc和lgβc的初值,其他i值时得到相应累积稳定常数对数值的初值.将上述初值代入上式lgΦMLi,max中可得到新的值,逐步迭代直至两次结果相等即为计算结果.文章使用了两个配合物体系进行计算,它们相邻两级稳定常数对数值差值最小仅为0.3,计算结果与真值一致.

The method for using integer slopes in determination of stability constants of coordination compound by extraction method is presented in this paper： Firstly,the integer slope points i-c（i=0,1,2,…,n） and their corresponding pL s（the negative logarithmic concentration of free ligand） at the first-order differential curve of the logarithmic distribution ratio lg D against pL are found,where i and c are the coordination numbers of coordination ion MLi and the coordination ion to be extracted,MLc.At these corresponding pLi s,it has lgD=lgλc＋（lgβc-lgβi）＋（i-c）pL＋lgMLi,max,where λc is the distribution constant of MLc between organic and water phases,βs are accumulative stability constants and MLi,max is the maximum distribution coefficient of MLi on water phase.Secondly,ignore lgMLi,maxat above equation can obtain the initial values of βi at different i,especially when i=c,0,and we can obtain initial values of lgλc and lgβc.Thirdly,putting these initial values into above equations,we can obtain new lgβis and lgλc,and continue to iterate until the results of two times are equal.Two coordination compound systems with the minimum difference of successive logarithmic stability constants is 0.3,and the results match with present values.