Matsumoto Yoshiteru, Honma Kenji
Graduate School of Material Science, University of Hyogo, 3-2-1 Kohto, Kamigori, Hyogo 678-1297, Japan.
J Chem Phys. 2009 Feb 7;130(5):054311. doi: 10.1063/1.3072495.
The hydrogen-bonded structures of pyrrole-solvent (H(2)O,CH(3)OH,C(2)H(5)OH) binary clusters were studied by the combination of experimental and theoretical techniques. Infrared cavity ringdown spectroscopy was applied to observe the NH and OH stretching vibrations of the clusters. The structures, binding energies, and normal modes of the binary clusters were obtained by quantum chemical calculations of the MP2/6-31+G(d,p) and B3LYP/6-311+G(d,p) levels. For the 1:1 clusters of pyrrole-H(2)O, pyrrole-CH(3)OH, and pyrrole-C(2)H(5)OH, the hydrogen-bonded NH stretching vibrations were observed at 3448, 3414, and 3408 cm(-1), respectively. They were redshifted from the NH stretching vibration of the pyrrole monomer, and the amounts of the redshift were proportional to the proton affinities of the solvent molecules. MP2 level calculations revealed that the sigma-type (NH...O) hydrogen-bonded structures had 7.6-9.0 kJ/mol larger binding energies than the pi-type structures (OH...pi electron cloud of pyrrole), and that the vibrational frequencies of the sigma-type structures are consistent with the observed spectra. In addition to the 1:1 clusters, the NH or OH stretching vibrations of pyrrole-CH(3)OH binary clusters were observed at 3432 and 3549 cm(-1). Among three optimized structures of the pyrrole-(CH(3)OH)(2), the sigma-pi bridge pyrrole-(CH(3)OH)(2) provided a reasonable agreement between the observed and calculated vibrational frequencies. For the pyrrole-H(2)O binary clusters, three new bands were observed at 3414, 3435, and 3541 cm(-1). These bands are consistent with the calculated NH and OH stretching vibrations of the (pyrrole)(2)-H(2)O cluster, which has a closed cyclic hydrogen-bonded structure.
通过实验和理论技术相结合的方法，研究了吡咯 - 溶剂（H₂O、CH₃OH、C₂H₅OH）二元团簇的氢键结构。应用红外腔衰荡光谱来观测团簇的NH和OH伸缩振动。通过MP2/6 - 31 + G(d,p)和B3LYP/6 - 311 + G(d,p)水平的量子化学计算，得到了二元团簇的结构、结合能和正则振动模式。对于吡咯 - H₂O、吡咯 - CH₃OH和吡咯 - C₂H₅OH的1:1团簇，观测到的氢键NH伸缩振动分别位于3448、3414和3408 cm⁻¹处。它们相对于吡咯单体的NH伸缩振动发生了红移，红移量与溶剂分子的质子亲和能成正比。MP2水平计算表明，σ型（NH...O）氢键结构的结合能比π型结构（OH...吡咯的π电子云）大7.6 - 9.0 kJ/mol，并且σ型结构的振动频率与观测光谱一致。除了1:1团簇外，还在3432和3549 cm⁻¹处观测到了吡咯 - CH₃OH二元团簇的NH或OH伸缩振动。在吡咯 - (CH₃OH)₂的三种优化结构中，σ - π桥连的吡咯 - (CH₃OH)₂在观测和计算的振动频率之间提供了合理的一致性。对于吡咯 - H₂O二元团簇，在3414、3435和3541 cm⁻¹处观测到了三个新的谱带。这些谱带与具有封闭环状氢键结构的(pyrrole)₂ - H₂O团簇的计算NH和OH伸缩振动一致。
