Abstract
It is known that the stability constant of crown ether complex with metal ion increases when the side-chain including the atom with coordinative ability is introduced in the crown framework. We have studied what kind of factors such as type, size, and electron density of atom on the side-chain are concerned in the increase in the stability constant using N-(2-substituted aryl)-monoaza-crown-ether. In order to elucidate the factor which decides the stability constant, the analysis on the temperature dependency of stability constant was carried out by the UV titration experiment by changing temperature. In this paper, the effect of 2-F side-chain will be discussed. Metal ions for present measurement are Na+, Li+ and Mg2+. The stability constant of Mg2+ complex decreased with the temperature descent, while that of Na+ and Li+ complex increased with the temperature descent. That is to say, the complexing with Na+ orLi+ is caused by the enthalpy decrease and the decrease is ca. 10 kJ/mol by 2-F substituent. On the other hand, the complexing with Mg2+ is caused by the entropy enhancement.
