稀土(III)与不饱和冠醚配位作用的热力学性质

用量热滴定法测定了2，3－二苯基-烯-2]-1，4，7，10，13-五氧杂环十五烷（以下称2，3-二苯基-烯-2]-15-冠-5）与稀土（Ⅲ）硝酸盐（La，Ce，Pr，Nd，Sm，Eu）在无水乙腈溶液中，298.15 K时配位作用的热力学性质．化学计量法表明，所有的稀土硝酸盐均与不饱和冠醚形成了1:1的配合物．实验中，由联接的计算机直接算出了配位物的稳定常数和配合作用的焓，进而算出了吉布斯自由能和配位熵. 结果表明，2，3-二苯基-烯-2]-15-冠-5与Pr(NO_3)_3形成的配位化合物，其稳定常数最高，并与15-冠-5的实验结果作了比较．从热力学的观点讨论了不饱和冠醚分子结构和阳离子的性质对配位稳定性的影响．

Complexation Thermodynamics of Rare Earch(III) Nitrates with Stibeno-15-Crown-5 in Anhydrous Acetonitrile

Calorimetric titrations have been performed in anthydrous acetonitrile at 298.15 K in order to obtain the complex stabillty constants(K_s) and the thermodynamic parameters for the complexation of rare earth(Ⅲ) nitrates (La, Ce, Pr, Nd, Sm, Eu) with 2,3-diphenyl-ene-(2)-1,4,7,10,13-pentaoxacyclopentadecane (Stilbeno-15-crown-5). The complexation stoichiometry is 1:1 for all rare earth(Ⅲ) nitrates. The complex stability constants (K_s), reaction enthalpies(△H~o) and entropies (△S~o) were calculated directly by using precision calorimeter connected to an personal microcomputer. The coordination of the unsaturated crown ether B (to see Fig.1) with Pr~(3+) showed the highest complexation ability and selectivity in the six kinds of rare earth (III) nitrates, and compared with the results of 15-crown-4A (in Fig.1). The thermodynamics quantities clearly indicate that the comples stability sequence is essentially entropy governed, although the complex formation itself is evidently enthalpy driven. The effects of unsaturated crown ether's molecular structure and cation's properties upon complex stability have been discussed from a viewpoint of thermodynamics.