Determination of the Crystal Structure of Hexaphenyldisilane from Powder Diffraction Data and Its Thermodynamic Properties

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• 作者：Thomas Bernert ; Bj枚rn Winkler ; Yasar Krysiak ; Lothar Fink ; Matthias Berger ; Edith Alig ; Lkhamsuren Bayarjargal ; Victor Milman ; Lars Ehm ; Peter W. Stephens ; Norbert Auner ; Hans-Wolfram Lerner
• 刊名：Crystal Growth & Design
• 出版年：2014
• 出版时间：June 4, 2014
• 年：2014
• 卷：14
• 期：6
• 页码：2937-2944
• 全文大小：524K
• 年卷期：v.14,no.6(June 4, 2014)
• ISSN：1528-7505

文摘

The crystal structure of hexaphenyldisilane, Si₂(C₆H₅)₆, was determined from synchrotron powder diffraction data. The compound crystallizes in orthorhombic space group P2₁2₁2₁ with the following unit cell dimensions: a = 20.2889(8) 脜, b = 16.9602(7) 脜, and c = 8.5506(4) 脜. Second-harmonic generation measurements as well as density functional theory calculations were used to confirm the structure determination. The combination of experimental and theoretical studies yields a Si鈥揝i distance [d(Si鈥揝i)] of 2.38 脜. The phenyl rings of a molecule are staggered and slightly distorted, so that the molecule is acentric. Thermodynamic measurements showed no phase transition in the temperature range of 2鈥?00 K. The molar heat capacity (C_p) at 298.15 K of 604(6) J mol^鈥? K^鈥? was established experimentally and by lattice dynamic calculations. The molar entropy (S掳) and the molar enthalpy (螖H) in the temperature range of 0鈥?98.15 K are 674(7) J mol^鈥? K^鈥? and 97(6) kJ mol^鈥? respectiveley. The Debye temperature (胃_D) is 207(5) K. The thermal expansion of Si₂(C₆H₅)₆ is strongly anisotropic, and negative in two directions as determined via temperature-dependent X-ray powder diffraction experiments. The linear thermal expansion coefficients at 298.15 K are as follows: 伪_a = 鈭?(2) 脳 10^鈥? K^鈥?, 伪_b = 鈭?(2) 脳 10^鈥? K^鈥?, and 伪_c = 2.21(4) 脳 10^鈥? K^鈥?. The volumetric thermal expansion coefficient (伪_V) at 298.15 K is 2.13(5) 脳 10^鈥? K^鈥?.