Conformation of alkali metal ion-calix[4]arene complexes investigated by IR spectroscopy in the gas phase
Conformation of alkali metal ion-calix[4]arene complexes investigated by IR spectroscopy in the gas phase
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通过气相红外光谱研究碱金属离子-杯[4]芳烃配合物的构象
DOI：
10.1039/c9cp03194d
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发表时间：
2019
影响因子：
3.3
通讯作者：
Inokuchi Yoshiya
中科院分区：
文献类型：
--
作者：
Wada Kozue;Kida Motoki;Muramatsu Satoru;Ebata Takayuki;Inokuchi Yoshiya
在冷(−10K)气相条件下，用红外-紫外双共振光谱测量了杯[4]芳烃(C4a)与K+、Rb+、Cs+的配合物在3200-3700 cm∼1区的红外光谱。所有的络合物都显示出两个谱带，可归属于C4a部分氢键OH基团的伸缩振动。量子化学计算预测了几种异构体具有不同的红外光谱，但“锥形”构象的红外光谱很好地再现了IR-UV光谱，表明所有的配合物都是锥形构象，包括锥形中的金属离子。随着离子尺寸从K+(3357和3513 cm−1)到Rb+(3323和3463 cm−1)和Cs+(3279和3379 cm−1)的增大，OH伸缩振动的频率降低，但显著高于裸C4a中的氢键OH基团(3158 cm−1)。这些结果表明，C4a通过扭曲锥形空穴来包裹金属离子，并且随着离子尺寸从K+增加到Cs+，锥形构象的扭曲程度进一步减小，OH基团之间的氢键变得更强。在碱金属离子络合物中，Cs+络合物对C4a空穴的畸变率最小。这可能是C4A在溶液中对Cs+离子的包裹性强于较小的碱金属离子的原因之一。
We measure the IR spectra of calix[4]arene (C4A) complexes with K+, Rb+, and Cs+ ions in the 3200–3700 cm−1 region by IR-UV double-resonance spectroscopy performed under cold (∼10 K) gas-phase conditions. All the complexes show two bands that can be assigned to the stretching vibrations of hydrogen-bonded OH groups in the C4A part. Quantum chemical calculations predict several isomers having different IR spectra, but the IR spectrum of the “cone” conformer reproduces the IR-UV spectrum very well, indicating that all the complexes adopt the cone conformation including the metal ions in the cone. The frequency of the OH stretching vibrations decreases with increasing the ion size from K+ (3357 and 3513 cm−1) to Rb+ (3323 and 3463 cm−1) and Cs+ (3279 and 3379 cm−1), but it is substantially higher than that of hydrogen-bonded OH groups in bare C4A (3158 cm−1). These results suggest that C4A encapsulates the metal ions by distorting the cone cavity, and that the distortion of the cone conformation is reduced more and the hydrogen bond between the OH groups becomes stronger with increasing the ion size from K+ to Cs+. The Cs+ complex has the smallest distortion of the C4A cavity among the alkali metal ion complexes. This can be one origin for the predominant encapsulation of Cs+ ions by C4A over smaller alkali metal ions in solution.