Kouderis Constantine, Tryfon Afrodite, Kabanos Themistoklis A, Kalampounias Angelos G
Physical Chemistry Laboratory, Department of Chemistry, University of Ioannina, GR-45110 Ioannina, Greece.
Section of Inorganic and Analytical Chemistry, Department of Chemistry, University of Ioannina, GR-45110 Ioannina, Greece.
Molecules. 2024 Feb 9;29(4):813. doi: 10.3390/molecules29040813.
Ultrasonic absorption measurements were carried out over a wide concentration and temperature range by means of a pulse technique to examine the structural mechanisms and the dynamical properties in thium exaethyliilazide (LiHMDS)-toluene solutions. Acoustic spectra revealed two distinct Debye-type relaxational absorptions attributed to the formation of trimers from dimeric and monomer units and to the formation of aggregates between a LiHMDS dimer and one toluene molecule in low and high frequencies, respectively. The formation of aggregates was clarified by means of molecular docking and DFT methodologies. The aggregation number, the rate constants and the thermodynamic properties of these structural changes were determined by analyzing in detail the concentration-dependent relaxation parameters. The low-frequency relaxation mechanism dominates the acoustic spectra in the high LiHMDS mole fractions, while the high-frequency relaxation influences the spectra in the low LiHMDS mole fractions. In the intermediate mole fraction region (0.25 to 0.46), both relaxations prevail in the spectra. The adiabatic compressibility, the excess adiabatic compressibility and the theoretically estimated mean free length revealed a crossover in the 0.25 to 0.46 LiHMDS mole fractions that signified the transition from one structural mechanism related with the hetero-association of LiHMDS dimers with toluene molecules to the other structural mechanism assigned to the formation of LiHMDS trimers. The combined use of acoustic spectroscopy with theoretical calculations permitted us to disentangle the underlying structural mechanisms and evaluate the volume changes associated with each reaction. The results were compared with the corresponding theoretically predicted volume changes and discussed in the context of the concentration effect on intermolecular bonding.
通过脉冲技术在较宽的浓度和温度范围内进行了超声吸收测量，以研究六甲基二硅氮锂（LiHMDS）-甲苯溶液中的结构机制和动力学性质。声学光谱揭示了两种不同的德拜型弛豫吸收，分别归因于在低频和高频下二聚体和单体单元形成三聚体以及LiHMDS二聚体与一个甲苯分子之间形成聚集体。通过分子对接和密度泛函理论（DFT）方法阐明了聚集体的形成。通过详细分析浓度依赖性弛豫参数，确定了这些结构变化的聚集数、速率常数和热力学性质。在高LiHMDS摩尔分数下，低频弛豫机制主导声学光谱，而在低LiHMDS摩尔分数下，高频弛豫影响光谱。在中间摩尔分数区域（0.25至0.46），两种弛豫在光谱中均占主导。绝热压缩性、过量绝热压缩性和理论估计的平均自由程在0.25至0.46的LiHMDS摩尔分数处显示出交叉点，这表明从与LiHMDS二聚体与甲苯分子的异质缔合相关的一种结构机制转变为与LiHMDS三聚体形成相关的另一种结构机制。声学光谱与理论计算的联合使用使我们能够解开潜在的结构机制，并评估与每个反应相关的体积变化。将结果与相应的理论预测体积变化进行了比较，并在分子间键合的浓度效应背景下进行了讨论。
