title: Fish-Bite structure by three-dimensional hydrogen-bond acceptor: IR spectroscopy of pyrrole and N-methylpyrrole binary clusters.
abstract: 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.
authors.affiliation: Graduate School of Material Science, University of Hyogo, 3-2-1 Kohto, Kamigori, Hyogo 678-1297, Japan. matsu@sci.u-hyogo.ac.jp
authors.forename: Yoshiteru
authors.initials: Y
authors.lastname: Matsumoto
authors.forename: Sunao
authors.initials: S
authors.lastname: Murakami
authors.forename: Kenji
authors.initials: K
authors.lastname: Honma
mesh_terms: D006860:Hydrogen Bonding; D015394:Molecular Structure; D011758:Pyrroles / Q000737:chemistry*; D011789:Quantum Theory; D013055:Spectrophotometry, Infrared
chemical_list: D011758:Pyrroles