Contribution of the π electron to the N-H···O=C hydrogen bond: IR spectroscopic studies of the jet-cooled pyrrole-acetone binary clusters.
Contribution of the π electron to the N-H···O=C hydrogen bond: IR spectroscopic studies of the jet-cooled pyrrole-acetone binary clusters.
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DOI：
10.1039/c2cp41564j
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发表时间：
2012-08
期刊：
影响因子：
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通讯作者：
Y. Matsumoto;Jun-ichi Iwamoto;K. Honma
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文献类型：
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作者：
Y. Matsumoto;Jun-ichi Iwamoto;K. Honma
为了研究 π 键合电子对 N-H…O=C 氢键（H-键）形成的贡献，我们将红外腔衰荡光谱应用于喷射冷却的吡咯-丙酮（Py-Ac）二元团簇。通过密度泛函理论 (DFT) 分析了观察到的 NH 伸缩振动，计算了不同尺寸的二元团簇的能量优化结构、谐波频率和相互作用能。我们观察到三个 NH 伸缩振动，归因于 3406、3388 和 3335 cm(-1) 处的双星团。这些分别被分配给 Py(2)-Ac(1)、Py(1)-Ac(1) 和 Py(1)-Ac(2) 簇的 H 键 NH 延伸。 Py(1)-Ac(1)簇具有具有C(s)对称性的单一N-H…O=C H键结构，而Py(1)-Ac(2)簇具有由单一N-H…O=C H键、偶极-偶极相互作用和弱CH H键形成的环状结构。进行自然键轨道 (NBO) 分析以揭示 Py-Ac 二元团簇中的氢键强度。对于Py(1)-Ac(2)簇，我们发现供体-受体相互作用不仅是n→σ*型（O原子孤对对到NH反键轨道），而且是π→σ*型（CO π键到NH反键轨道）。通过分析供体-受体相互作用中频移与稳定能之间的关系，我们得出结论，Py(1)-Ac(2)中NH伸缩振动较大的红移不仅可以通过孤对电子和π电子对N-H·O=C H键的贡献来解释，还可以通过Py与非H键Ac之间的偶极子相互作用来解释。我们还讨论了 Py(2)-Ac(1) 簇的结构。
To investigate the π bonding electron contribution to N-H···O=C hydrogen-bond (H-bond) formation, we applied IR cavity ringdown spectroscopy to jet-cooled pyrrole-acetone (Py-Ac) binary clusters. The observed NH stretching vibrations were analyzed by density functional theory (DFT), in which the energetically optimized structures, harmonic frequencies, and interaction energies were calculated for various sizes of binary clusters. We observed three NH stretching vibrations, ascribed to binary clusters at 3406, 3388, and 3335 cm(-1). These were assigned to H-bonded NH stretches of the Py(2)-Ac(1), Py(1)-Ac(1), and Py(1)-Ac(2) clusters, respectively. The Py(1)-Ac(1) cluster has a single N-H···O=C H-bonded structure with C(s) symmetry, while the Py(1)-Ac(2) cluster has a cyclic structure formed by a single N-H···O=C H-bond, dipole-dipole interactions, and weak CH H-bonds. A natural bond orbital (NBO) analysis was performed to reveal the H-bond strength in Py-Ac binary clusters. For the Py(1)-Ac(2) cluster, we found that the donor-acceptor interactions are not only the n →σ* type (O atom lone pair to the NH anti-bonding orbitals), but also the π→σ* type (the CO π bonding to the NH anti-bonding orbitals). By analyzing the relationship between the frequency shift and the stabilization energy in donor-acceptor interactions, we concluded that larger red-shift of the NH stretching vibration in the Py(1)-Ac(2) can be explained by not only the lone pair and the π electron contributions to the N-H···O=C H-bond, but also the dipole-interaction between Py and non-H-bonded Ac. We also discussed the structures of Py(2)-Ac(1) clusters.