Graduate School of Material Science, University of Hyogo, 3-2-1 Kohto, Kamigori, Hyogo 678-1297, Japan.
J Chem Phys. 2012 Aug 21;137(7):074307. doi: 10.1063/1.4746122.
The N-H...π hydrogen-bonded (H-bonded) structures of pyrrole (Py) and N-methylpyrrole (NMPy) binary clusters have been studied by IR cavity ringdown spectroscopy and density functional theory calculations. The Py(1)-NMPy(1) cluster has an "L-shape" structure, which is formed by an ordinary H-bond between a N-H donor of Py and a π-electron cloud acceptor of NMPy. The Py(2)-NMPy(1) cluster has a "Cyclic" structure, which is also formed by ordinary N-H...π H-bonds as well as the weak C-H...π H-bond between the methyl CH group and the π cloud acceptor of Py. On the other hand, the Py(1)-NMPy(2) cluster shows an extraordinary structure, in which the single donor NH group is surrounded by a three-dimensional H-bond acceptor formed by two aromatic π electron clouds. We call the Py(1)-NMPy(2) cluster as the "Fish-Bite" structure. The Py(1)-NMPy(2) cluster exhibits a redshifted NH stretch by 157 cm(-1) from the Py monomer, which is larger than 94 cm(-1) of the Py(1)-NMPy(1) cluster. However, both Py(1)-NMPy(1) and Py(1)-NMPy(2) clusters have calculated IR intensities of 169 and 163 km/mol, respectively. This result indicates that not only the N-H...π H-bonds but also the dipole-dipole interaction between Py and NMPy contributes to the Fish-Bite Py(1)-NMPy(2) cluster formation.
吡咯（Py）和 N-甲基吡咯（NMPy）二元团簇的 N-H…π 氢键（H 键）结构已通过红外腔衰荡光谱和密度泛函理论计算进行了研究。Py(1)-NMPy(1) 团簇具有“L 形”结构，由 Py 的 N-H 供体与 NMPy 的π 电子云受体之间的普通 H 键形成。Py(2)-NMPy(1) 团簇具有“环状”结构，它也是由普通的 N-H…π H 键以及甲基 CH 基团与 Py 的π 电子云受体之间的弱 C-H…π H 键形成的。另一方面，Py(1)-NMPy(2) 团簇显示出一种特殊的结构，其中单个供体 NH 基团被由两个芳族π 电子云形成的三维 H 键受体包围。我们称 Py(1)-NMPy(2) 团簇为“鱼咬”结构。Py(1)-NMPy(2) 团簇的 NH 伸缩振动向红移 157 cm(-1)，与 Py 单体相比，这一数值大于 Py(1)-NMPy(1) 团簇的 94 cm(-1)。然而，Py(1)-NMPy(1) 和 Py(1)-NMPy(2) 团簇的计算红外强度分别为 169 和 163 km/mol。这一结果表明，不仅是 N-H…π H 键，而且 Py 和 NMPy 之间的偶极-偶极相互作用也有助于形成“鱼咬”Py(1)-NMPy(2) 团簇。
