Complexation Thermodynamics of p-tert-Butylcalix[4]arene Derivatives with Light Lanthanoid Nitrates in Acetonitrile |
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Authors: | Yu Liu Shang Li Xiao-Peng Bai Takehiko Wada Yoshihisa Inoue |
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Affiliation: | 1. Department of Chemistry , Nankai University , Tianjin, 300071, China;2. Department of Molecular Chemistry , Osaka University , 2-1 Yamadaoka, Suita, 565-0871, Japan;3. Inoue Photochirogenesis Project , ERATO, JST , 4-6-3 Kamishinden, Toyonaka, 565-0085, Japan;4. Department of Molecular Chemistry , Osaka University , 2-1 Yamadaoka, Suita, 565-0871, Japan |
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Abstract: | Abstract Calorimetric titrations have been performed for the first time in anhydrous acetonitrile at 25°C to give the complex stability constant (K S) and thermodynamic quantities for the complexation of light lanthanoid(III) nitrates (La-Gd) with 5,11,17,23-tetra-tert-butyl-26,28-bis(cyanomethoxy)-25,27-dihydroxy-calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-26, 28-bis(2-aminoethoxy)-25,27-dihydroxycalix[4]arene (2). X-ray crystallographic structures of 1 and 2 were also determined and compared. Possessing the cyanomethoxy and aminoethyl substituents, 1 and 2 displayed strikingly different cation binding abilities and selectivity profiles with much higher K S values for La3+ and Ce3+, which may be related to the original structures in the solid state. Thus, the binding profile for 2 showed a rapid decrease in K S with decreasing ionic diameter from La3+ to Pr3+ and then became flat up to Gd3+, while 1 gave a very flat profile which is superimposable with that for 2 between Pr3+-Gd3+. Thermodynamically, the complexation is driven absolutely by enthalpy which compensates the entropic loss arising from the structural freezing of the calix[4]arene derivatives upon simultaneous binding of lanthanoid ion by the phenolic oxygen and acetonitrile molecule in the cavity. The general validity and the meaning of the compensative enthalpy-entropy relationship observed are discussed. |
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Keywords: | Calix[4]arene derivatives Calorimetric titration Complexation thermodynamics Light lanthanoid cations Ions selectivities |
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