Calorimetric Study on Coordination of Tridentate Imidazolyl Calix[6]arene Ligands to Zinc Ion in Organic Solvents
Calorimetric Study on Coordination of Tridentate Imidazolyl Calix[6]arene Ligands to Zinc Ion in Organic Solvents
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DOI：
10.1021/ic200809k
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发表时间：
2011-07-04
影响因子：
4.6
通讯作者：
Reinaud, Olivia
中科院分区：
文献类型：
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作者：
Kano, Koji;Kondo, Masataka;Reinaud, Olivia
采用等温滴定量热法研究了三种含对位取代基的三咪唑基杯[6]芳烃（Calix-tBu，R-1 = R-2 = tert-butyl; Calix-NH2，R-1 = tert-butyl，R-2 = NH2; Calix-NO2，R-1 = tert-butyl，R-2 = NO2）与Zn（ClO4）（2）（H2O）（6）在乙腈、甲醇和THF中的络合作用。对于这些杯芳烃配体在乙腈中与Zn（II）的配位，获得了典型的单相放热滴定曲线，表明配体与Zn（II）形成1：1配合物，并伴随着配体的大的构象变化。相反，在甲醇中的络合是吸热的，并由有利的熵变为主。通过从Zn（II）和配体的广泛去溶剂化来实现熵增益。ITC测量表明在过量配体（Calix-NH2和Calix-NO2）存在下在THF中形成2：1配体-Zn（II）络合物。在进一步加入Zn（ClO4）（2）（H2O）（6）后，2：1络合物转化为1：1络合物。结果表明，在配体过量的条件下，配位溶剂乙腈对直接形成1：1配合物具有重要作用。还通过ITC研究了ditopic配体（Calix-Tri）与在较宽边缘上的三个三唑部分的络合。咪唑部分与Zn（II）的第一配位是放热过程。其次是熵有利的三唑部分的二价阳离子的配位。我们还研究了交换的第四个配体（H2O）的锌（II）配合物的杯-NH 2与丁胺，庚胺，aceronitrile，和乙酰胺在非竞争性溶剂，THF。随着客体配体能力的增加，Δ H-0趋于降低，而由于客体配体在杯芳烃腔体内的旋转受限，Δ H-0也受到熵项的影响。
Complexation of three kinds of tris(imidazolyl)-calix[6]arenes containing alternate p-substituents (Calix-tBu, R-1 = R-2 = tert-butyl; Calix-NH2, R-1 = tert-butyl, R-2 = NH2; Calix-NO2, R-1 = tert-butyl, R-2 = NO2) with Zn(ClO4)(2)(H2O)(6) in acetonitrile, methanol, and THF was investigated via isothermal titration calorimetry (ITC). For the coordination of these calixarene ligands to Zn(II) in acetonitrile, typical one-phase exothermic titration curves were obtained, indicating the formation of 1:1 ligand-Zn(II) complexes accompanied by large conformational changes of the ligands. In contrast, the complexation in methanol was endothermic and dominated by favorable entropy changes. The entropy gains were achieved by extensive desolvation from both Zn(II) and the ligands. ITC measurements suggest a 2:1 ligand-Zn(II) complex formation in THF in the presence of excess ligands (Calix-NH2 and Calix-NO2). The 2:1 complexes were converted to 1:1 complexes upon further addition of Zn(ClO4)(2)(H2O)(6). The results indicate the important role of a coordinating solvent (acetonitrile) for direct formation of the 1:1 complexes under the conditions of excess ligand. Complexation of a ditopic ligand (Calix-Tri) with three triazole moieties on the wider rim was also studied via ITC. The first coordination of the imidazole moieties to Zn(II) was an exothermic process. This was followed by the entropically favorable coordination of the triazole moieties to the divalent cation. We have also investigated exchange of the fourth ligand (H2O) of the Zn(II) complex of Calix-NH2 with butylamine, heptylamine, aceronitrile, and acetamide in a noncompetitive solvent, THF. The Delta H-0 tended to decrease upon increasing the ability of the guest ligand, whereas it was also affected by an entropic term due to restricted rotation of the guest ligand inside the calixarene cavity.