Solvent Effects on the Encapsulation of Divalent Ions by Benzo-18-Crown-6 and Benzo-15-Crown-5
Solvent Effects on the Encapsulation of Divalent Ions by Benzo-18-Crown-6 and Benzo-15-Crown-5
复制标题
溶剂对 Benzo-18-Crown-6 和 Benzo-15-Crown-5 包封二价离子的影响
DOI：
10.1021/acs.jpca.5b04450
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发表时间：
2015
期刊：
影响因子：
2.9
通讯作者：
and Thomas R. Rizzo
中科院分区：
文献类型：
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作者：
Yoshiya Inokuchi;Takayuki Ebata;and Thomas R. Rizzo
我们测量了冷的苯并-15-冠-5(B15C5)和苯并-18-冠-6(B18C6)与二价离子(M2+=Ca2+，Sr2+，Ba2+和Mn2+)的紫外光解离(UVPD)光谱，并用水或CH3OH分子：M2+·B15C5·H2O，M2+·B15C5·CH3OH，M2+·B18C6·H2O和M2+·B18C6·CH3OH进行了研究。所有物种在36600-37600 cm-1区域都显示出许多尖锐的振动带，这可以归因于B18C6或B15C5组分的电子跃迁。通过IR-UV双共振光谱在OH伸缩区域获得了这些配合物的构象特异性红外光谱。所有H2O络合物的IR-UV光谱在∼3610和∼3690 cm~(-1)处都有IR谱带，这些谱带可归属于H2O组分的对称和不对称的OH伸缩振动。CH_3OH络合物在∼3630 cm~(-1)处还表现出OH基团的伸缩振动。在所有络合物中，H_2O和CH_3OH组分通过M2+···O键直接键合到M2+离子上，但构象上的微小差异导致了OH伸缩频率的显著不同，这使得我们能够确定构象的数目。对于Ca2+、Sr2+和Mn2+，B18C6络合物的构象数在2-5之间，明显大于B15C5(1或2)的络合物。而对于Ba2+，B18C6(1或2)的构象数与B15C5的构象数几乎相同。这可能是因为Ba2+离子太大，不能位于B15C5和B18C6的空穴中心，这为Ba2+离子提供了一个开放的位置，适合与H2O或CH3OH溶剂化。络合物的构象越多，它在非零温度下的熵优势就越大。因此，较多的构象表明，在溶剂化条件下，络合物的稳定性较高，导致离子在溶液中的包裹度较高。
We measure UV photodissociation (UVPD) spectra of cold benzo-15-crown-5 (B15C5) and benzo-18-crown-6 (B18C6) complexes with divalent ions (M2+= Ca2+, Sr2+, Ba2+, and Mn2+), solvated with an H2O or a CH3OH molecule: M2+·B15C5·H2O, M2+·B15C5·CH3OH, M2+·B18C6·H2O, and M2+·B18C6·CH3OH. All the species show a number of sharp vibronic bands in the 36600–37600 cm–1region, which can be attributed to electronic transitions of the B18C6 or B15C5 component. Conformer-specific IR spectra of these complexes are also obtained by IR-UV double-resonance spectroscopy in the OH stretching region. All the IR-UV spectra of the H2O complexes show IR bands at ∼3610 and ∼3690 cm–1; these bands can be assigned to the symmetric and asymmetric OH stretching vibrations of the H2O component. The CH3OH complexes also show the stretching vibration of the OH group at ∼3630 cm–1. The H2O and the CH3OH components are directly bonded to the M2+ion through the M2+···O bond in all the complexes, but a small difference in the conformation results in a noticeable difference in the OH stretching frequency, which enables us to determine the number of conformers. For Ca2+, Sr2+, and Mn2+, the number of conformers for the B18C6 complexes is in the range of 2–5, which is clearly larger than complexes with B15C5 (1 or 2). However, for Ba2+the number of conformers with B18C6 (1 or 2) is almost the same as that with B15C5. This is probably because the Ba2+ion is too large to be located in the cavity center of either B15C5 and B18C6, which provides an open site at the Ba2+ion suitable for solvation with H2O or CH3OH. The more conformations a complex can take, the more entropically favored it is at nonzero temperatures. Hence, the larger number of conformations suggests higher stability of the complexes under solvated conditions, leading to a higher degree of ion encapsulation in solution.