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

• Published in: Crystal growth & design Vol. 14; no. 6; pp. 2937 - 2944
• Main Authors: Bernert, Thomas, Winkler, Björn, Krysiak, Yasar, Fink, Lothar, Berger, Matthias, Alig, Edith, Bayarjargal, Lkhamsuren, Milman, Victor, Ehm, Lars, Stephens, Peter W, Auner, Norbert, Lerner, Hans-Wolfram
• Format: Journal Article
• Language: English
• Published: Washington,DC American Chemical Society 04.06.2014
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Electron states; Exact sciences and technology; Methods of electronic structure calculations; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; Physics; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Thermal properties of condensed matter; Thermal properties of crystalline solids; Thermodynamic properties; Temperature dependence; Second harmonic generation; Transition temperature; Space groups; Enthalpy; Heat capacity; Theoretical study; Entropy; XRD; Experimental study; Phase transitions; Thermal properties; Debye temperature; Thermal expansion; Unit cell; Powder pattern; Anisotropy; Lattice dynamics; Optical properties; Thermal expansion coefficient; Density functional method; Orthorhombic lattices; Thermodynamic properties; Crystal structure
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg5002286

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) Å, b = 16.9602(7) Å, and c = 8.5506(4) Å. 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–Si distance [d(Si–Si)] of 2.38 Å. 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 2–400 K. The molar heat capacity (Cp ) at 298.15 K of 604(6) J mol–1 K–1 was established experimentally and by lattice dynamic calculations. The molar entropy (S°) and the molar enthalpy (ΔH) in the temperature range of 0–298.15 K are 674(7) J mol–1 K–1 and 97(6) kJ mol–1 respectiveley. The Debye temperature (θD) 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: α a = −4(2) × 10–6 K–1, α b = −4(2) × 10–6 K–1, and α c = 2.21(4) × 10–4 K–1. The volumetric thermal expansion coefficient (α V ) at 298.15 K is 2.13(5) × 10–4 K–1.