Ignatyev Igor S, Partal F, López González J J, Sundius Tom
Departamento de Química Física y Analítica, Facultad de Ciencias Experimentales, Universidad de Jaén, Campus Universitario de "Las Lagunillas", Edif B-3, E-23071 Jaén, Spain.
Spectrochim Acta A Mol Biomol Spectrosc. 2004 Apr;60(5):1169-78. doi: 10.1016/j.saa.2003.07.004.
The assignment of the SiOH group vibrations of trimethylsilanol, which is still controversial, is proposed. This assignment is based on theoretical B3LYP force field scaled using the constants of the (CH3)3Si group optimized to fit experimental vibrational frequencies of (CH3)3SiF and (CD3)3SiF molecules as well as the OH stretching scale factor from methanol. The ab initio force field defined in this way gives a good agreement of the theoretical vibrational frequencies of trimethylsilanol with the positions of IR and Raman bands observed in the gas phase. This force field predicts the greatest contribution of the delta SiOH coordinates to the vibration with frequency of 804 cm(-1). The elimination of the coupling of the SiOH deformation with methyl rocking modes by the normal coordinate treatment of (CD3)3SiOH gives 832 cm(-1) for silanol deformation which is in a good agreement with the 834 cm(-1) value proposed earlier for the bending mode of free silanol groups. The geometry and force field of the open chain H3SiOH trimer is computed to model the change of the delta SiOH frequencies upon formation of the hydrogen-bonded polymers. This model predicts a significant shift of SiOH bending frequencies to the 1000-1200 cm(-1) range while those of SiOD to the 800-850 cm(-1) range. These predictions allow us to ascribe the 1087 cm(-1) band observed in the IR spectrum of crystalline (CH3)3SiOH and the Raman 775 cm(-1) band of the liquid (CH3)3SiOD to deformations of the hydrogen-bonded silanol groups.
提出了关于三甲基硅醇中SiOH基团振动归属的问题，该问题仍存在争议。这一归属基于理论B3LYP力场，该力场通过对(CH3)3Si基团的常数进行缩放来优化，以拟合(CH3)3SiF和(CD3)3SiF分子的实验振动频率，以及来自甲醇的OH伸缩比例因子。以这种方式定义的从头算力场使得三甲基硅醇的理论振动频率与在气相中观察到的红外和拉曼谱带位置具有良好的一致性。该力场预测，在804 cm(-1)频率的振动中，δSiOH坐标贡献最大。通过对(CD3)3SiOH进行简正坐标处理，消除SiOH变形与甲基摇摆模式的耦合，得到硅醇变形的频率为832 cm(-1)，这与先前提出的游离硅醇基团弯曲模式的834 cm(-1)值吻合良好。计算了开链H3SiOH三聚体的几何结构和力场，以模拟氢键聚合物形成时δSiOH频率的变化。该模型预测SiOH弯曲频率将显著移至1000 - 1200 cm(-1)范围，而SiOD的弯曲频率移至800 - 850 cm(-1)范围。这些预测使我们能够将在结晶(CH3)3SiOH的红外光谱中观察到的1087 cm(-1)谱带以及液体(CH3)3SiOD的拉曼775 cm(-1)谱带归属于氢键硅醇基团的变形。
