Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai 400 005, India.
Phys Chem Chem Phys. 2010 Jul 7;12(25):6650-9. doi: 10.1039/b924288k. Epub 2010 Apr 21.
Although the first experimental report on the blue shifted hydrogen bond in gas phase appeared about a decade ago, not many examples have been reported in the literature thereafter. Computational studies on systems exhibiting such blue shifted hydrogen bond however have been abundant since then. Many of these theoretical predictions remain to be verified experimentally. In this work we present an example of blue shifted hydrogen bond observed in the weakly bound complexes of 3-methylindole and CHX(3) (X = F, Cl). The complexes were prepared using the supersonic jet expansion method and studied using the laser spectroscopic methods. The key findings were that these complexes exhibit C-Hpi type hydrogen bonding interaction and the CH is bound to the phenyl part of the aromatic plane. The CH stretch was found to be blue shifted by 2 and 16 cm(-1) in the case of CHCl(3) and CHF(3), respectively. Ab initio calculations along with atoms-in-molecule analysis and natural bond orbital analysis support the experimental findings. The computed results at the DFT/MP2 level also indicated that the IR intensity of the H-bond donor CH-stretch increases by two to three orders of magnitude for the CHCl(3) complex whereas for the fluoroform complex the same decreases by an order of magnitude, which are consistent with the trend reported in the case of C-HO type of blue shifting hydrogen bonds.
虽然关于气相中蓝移氢键的第一个实验报告出现在大约十年前，但此后文献中报道的例子并不多。然而，自那时以来，对表现出这种蓝移氢键的系统进行的计算研究一直很丰富。其中许多理论预测仍有待实验验证。在这项工作中，我们展示了在 3-甲基吲哚和 CHX(3)（X = F、Cl）的弱束缚复合物中观察到的蓝移氢键的一个例子。复合物是使用超音速喷射扩展方法制备的，并使用激光光谱方法进行了研究。主要发现是这些复合物表现出 C-Hpi 型氢键相互作用，并且 CH 与芳环平面的苯基部分结合。在 CHCl(3)和 CHF(3)的情况下，分别发现 CH 伸缩蓝移了 2 和 16 cm(-1)。从头算计算以及原子在分子中的分析和自然键轨道分析支持实验结果。DFT/MP2 水平的计算结果还表明，对于 CHCl(3)复合物，H 键供体 CH 伸缩的 IR 强度增加了两到三个数量级，而对于氟仿复合物，相同的强度降低了一个数量级，这与 C-HO 型蓝移氢键的报告趋势一致。
