ENTHALPY AND ENTROPY OF FORMATION OF ALKALI AND ALKALINE-EARTH MACROBICYCLIC CRYPTATE COMPLEXES
ENTHALPY AND ENTROPY OF FORMATION OF ALKALI AND ALKALINE-EARTH MACROBICYCLIC CRYPTATE COMPLEXES
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DOI：
10.1002/hlca.19760590414
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发表时间：
1976-01-01
影响因子：
1.8
通讯作者：
SAUVAGE, JP
中科院分区：
文献类型：
--
作者：
KAUFFMANN, E;LEHN, JM;SAUVAGE, JP
通过量热测量和先前确定的稳定常数[2]，得到了碱金属和碱土金属阳离子与几种大双环配体络合的焓和熵。焓和熵的变化对配合物的稳定性和选择性起着重要的作用。特别值得注意的是碱阳离子配合物（Na+, K+， Rb+和Cs+隐态）的大焓和负熵。Sr2+和Ba2+以及[Li+∧2.1.1]和[Na+∧2.2.1]密语属于焓优势型，也具有有利的熵变。Ca2+和[Li+∧2.2.1]晶体是完全熵稳定的，反应热约为零。与大单环复合物相比，大双环复合物的高稳定性，即隐位效应，通常是焓源性的。络合焓表现出选择性峰，稳定性也表现出选择性峰，而熵变则没有。考虑到M2+和M+阳离子的熵项所起的非常不同的作用，当考虑到焓时，用自由能表示的M2+/M+高选择性可能会被逆转。结联的焓和熵表明，无论包含哪个阳离子，隐阴离子的熵都是相似的，配体尽管比水合壳更坚硬，但仍能在一定程度上适应阳离子。这一结论与已发表的X射线数据一致。从配体的结构特征和溶剂化效应的角度讨论了络合焓和熵的来源。
The enthalpies and entropies of complexation of alkali and alkaline‐earth metal cations by several macrobicyclic ligands have been obtained from calorimetric measurements and from the previously determined stability constants [2]. Both enthalpy and entropy changes play an important role in the stability and selectivity of the complexes. Particularly noteworthy are thelarge enthalpiesand thenegative entropiesof complexation obtained for the alkali cation complexes (Na+, K+, Rb+and Cs+cryptates). The Sr2+and Ba2+as well as [Li+⊂ 2.1.1] and [Na+⊂ 2.2.1] cryptates are of the enthalpy dominant type with also a favourable entropy change. The Ca2+and [Li+⊂ 2.2.1] cryptates are entirely entropy stabilized with about zero heat of reaction. The high stability of the macrobicyclic complexes as compared to the macromonocylcic ones, thecryptate effect, is ofenthalpic origin. The enthalpies of complexation display selectivity peaks, as do the stabilities, whereas the entropy changes do not. The high M2+/M+selectivities found in terms of free energy, may be reversed when enthalpy is considered in view of the very different role played by the entropy term for M2+and M+cations. The enthalpies and entropies of ligation show that whereas the cryptate anions are similar in terms of entropy irrespective of which cation is included, the ligands, despite being more rigid than the hydration shell, are nevertheless able to adjust to some extent to the cation. This conclusion agrees with published X‐rays data. The origin of the enthalpies and entropies of complexation is discussed in terms of structural features of the ligands and of solvation effects.