Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
J Phys Chem A. 2010 Jan 28;114(3):1514-20. doi: 10.1021/jp907838r.
Argon-tagged alkali metal ion-crown ether complexes were generated in the gas phase and investigated using a combination of infrared predissociation (IRPD) spectroscopy, density functional, and symmetry-adapted perturbation theory (SAPT). The IRPD spectra of M(+)(12-crown-4 ether)Ar and M(+)(18-crown-6 ether)Ar, where M = Li, Na, K, Rb, and Cs, were collected in the CH stretching region, using the argon-messenger technique. The gas-phase neutral vibrations for each crown ether shift to higher frequency when complexed to an alkali metal ion. Similarities in the experimental IRPD spectra of Li(+)(12-crown-4 ether)Ar and Li(+)(18-crown-6 ether)Ar indicate that the binding of Li(+) is similar for both crown ethers. In the 12-crown-4 ether systems, there are trackable changes with ion size in the IRPD spectra until the point is reached where the ion is too large to bind to the interior of the macrocycle. Starting with Na(+), the 18-crown-6 spectra vary only slightly as the ion size is increased. The overall profiles of the IRPD spectra indicate that a similar configuration of the complexes is adopted for the ions larger than Na(+). The calculated SAPT interaction energies mirror the trends exhibited by the IRPD spectra and provide interesting insights on the roles of the different interaction energy components in binding the cation to the crown-ether.
氩标记的碱金属离子-冠醚配合物在气相中生成，并结合红外预解离（IRPD）光谱、密度泛函和对称自适应微扰理论（SAPT）进行研究。使用氩信使技术，在 CH 伸缩区域中收集了 M(+)(12-冠-4 醚)Ar 和 M(+)(18-冠-6 醚)Ar（其中 M = Li、Na、K、Rb 和 Cs）的 IRPD 光谱。与碱金属离子配位时，每个冠醚的气相中性振动向更高频率移动。Li(+)(12-冠-4 醚)Ar 和 Li(+)(18-冠-6 醚)Ar 的实验 IRPD 光谱具有相似性，表明 Li(+)的结合对于两种冠醚都是相似的。在 12-冠-4 醚体系中，随着离子尺寸的变化，IRPD 光谱中存在可追踪的变化，直到离子太大而无法结合到大环的内部。从 Na(+)开始，随着离子尺寸的增加，18-冠-6 光谱的变化很小。IRPD 光谱的整体轮廓表明，对于大于 Na(+)的离子，采用了类似的配合物构型。计算出的 SAPT 相互作用能反映了 IRPD 光谱所表现出的趋势，并为阳离子与冠醚结合的不同相互作用能成分的作用提供了有趣的见解。
