Rotational dynamics in a crystalline molecular gyroscope by variable-temperature 13C NMR, 2H NMR, X-ray diffraction, and force field calculations
Rotational dynamics in a crystalline molecular gyroscope by variable-temperature 13C NMR, 2H NMR, X-ray diffraction, and force field calculations
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DOI：
10.1021/ja064325c
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发表时间：
2007-01-31
影响因子：
15
通讯作者：
Garcia-Garibay, Miguel A.
中科院分区：
文献类型：
--
作者：
Khuong, Tinh-Alfredo V.;Dang, Hung;Garcia-Garibay, Miguel A.
结合固体C-13CPMAS核磁共振、H-2核磁共振、X射线各向异性位移参数(ADP)和分子力学计算，分析了1，4-bis[3，3，3-tris(m-methoxyphenyl)propynyl]benzene(3A)的转动动力学。VT C-13 CPMAS的线形分析与宽带H-2核磁共振的线形分析结果非常一致，转动势垒分别为11.3kcal/mol和11.5kcal/mol。在正弦电势下，对100 K和200 K下单晶X射线衍射法得到的ADPs进行分析，得到的势垒分别为10.3和10.1千卡。对300K下获得的数据进行的X射线结构的类似分析表明，势垒只有8.0kcal/mol。最后，用分子力学的有限团簇模型计算的旋转势揭示了一个对称但非正弦的势，它相对较好地解释了X射线衍生值和核磁共振实验结果。由低温和高温X射线数据得到的势垒之间的差异可能是由于在较高的温度值下非谐性的增加或无序性的增加。
A combination of solid-state C-13 CPMAS NMR, H-2 NMR, X-ray-determined anisotropic displacement parameters (ADPs), and molecular mechanics calculations were used to analyze the rotational dynamics of 1,4-bis[3,3,3-tris(m-methoxyphenyl)propynyl]benzene (3A), a structure that emulates a gyroscope with a p-phenylene group acting as a rotator and two m-methoxy-substituted trityl groups acting as a stator. The line shape analysis of VT C-13 CPMAS and broad-band H-2 NMR data were in remarkable agreement with each other, with rotational barriers of 11.3 and 11.5 kcal/mol, respectively. The barriers obtained by analysis of ADPs obtained by single-crystal X-ray diffraction at 100 and 200 K, assuming a sinusoidal potential, were 10.3 and 10.1 kcal, respectively. A similar analysis of an X-ray structure solved from data acquired at 300 K suggested a barrier of only 8.0 kcal/mol. Finally, a rotational potential calculated with a finite cluster model using molecular mechanics revealed a symmetric but nonsinusoidal potential that accounts relatively well for the X-ray-derived values and the NMR experimental results. It is speculated that the discrepancy between the barriers derived from low and high-temperature X-ray data may be due to an increase in anharmonicity, or to disorder, at the higher temperature values.