冠醚配位作用的热力学性质——水液溶中1,4,7,10,13,16-六氧杂环十八烷与若干钾盐配位作用的负离子效应

本文用量热滴定法测定了1,4,7,10,13,16-六氧杂环十八烷(以下称18-冠-6)与KCl,KBr,KI, KClO_4,KNO_3,KBrO_3及K_2S_2O_3共八种钾盐在水溶液中, 25 ℃时的配位作用, 直接计算了配合物稳定常数及配位反应热。实验结果表明, 18-冠-6与KNO_3,K_2S_2O_3形成的配位化合物, 其稳定常数最高。讨论了阴离子对配位稳定性的影响。

A STUDY ON THERMODYNAMIC PROPERTIES OF CROWN ETHER COMPLEXATION——EFFECT OF ANIONS ON THE COMPLEXATION OF 1,4,7,10,13,16-HEXAOXACYCLOOCTADECAN WITH SOME POTASSIUM SALTS IN AQUEOUS SOLUTION

Thermodynamic properties of the complexation of 18-crown-6 with KCI, KBr, KI, KClO_4, KNO_3, KBrO_3,K_2CO_3 and K_2S_2O_8 in water solution were studied at 25 ℃ by calorimetric titration. The stability constants of coordination compounds and enthalpies of coordination were calculated directly.It was shown that among the calculated volues the stability constants of coordination compounds formed by 18-crown-6 with KNO_3 and K_2S_2O_8 were the highest. The influence of anions on the stability of coordination compounds may be that:(1) The concomitant anions have effection the ligand conformation, which will cause considerable changes in the entropy of complexation and the enthalpy of complexation; (2) The strength of bonding force of anion-K~+ effects the strength of ion-dipole bond of K~+-ligand; (3) The hydration of anion itself also effects the complexation of K~+ with crown ether.The sequence of the stability constants of coordination compounds of 18-crown-6 with the 8 potassium salts is S_2O_8~(2-)>NO_3~->CO_3~(2-)>Br~->Cl~->I~->ClO_4~->BrO_3~-. The order of salts in the complexation enthalpy sequence is, however, different.