Influence of the molecular structures on the high-pressure and low-temperature phase transitions of plastic crystals
(2003) In Acta Crystallographica. Section B: Structural Science 59(1). p.60-71- Abstract
The crystal structures of tert-butyl-tris(trimethylsilyl)silane, Si[C(CH3)3]1[Si(CH3)3]3 (Bu1), and di-ferr-butyl-bis(trimethylsilyl)silane, Si[C(CH3) 3]2[Si(CH3)3]2 (Bu2), at room temperature and at 105 K have been determined by X-ray powder diffraction; the high-pressure behavior for pressures between 0 and 5 GPa is reported. The room-temperature structures have cubic Fm3→m symmetry (Z = 4) with a = 13.2645 (2) Å, V= 2333.87 (4) Å3 for Bu1 and a = 12.9673 (1) Å, V = 2180.46 (3) Å3 for Bu2. The molecules are arranged in a cubic close packing (c.c.p.) and exhibit at least 48-fold orientational... (More)
The crystal structures of tert-butyl-tris(trimethylsilyl)silane, Si[C(CH3)3]1[Si(CH3)3]3 (Bu1), and di-ferr-butyl-bis(trimethylsilyl)silane, Si[C(CH3) 3]2[Si(CH3)3]2 (Bu2), at room temperature and at 105 K have been determined by X-ray powder diffraction; the high-pressure behavior for pressures between 0 and 5 GPa is reported. The room-temperature structures have cubic Fm3→m symmetry (Z = 4) with a = 13.2645 (2) Å, V= 2333.87 (4) Å3 for Bu1 and a = 12.9673 (1) Å, V = 2180.46 (3) Å3 for Bu2. The molecules are arranged in a cubic close packing (c.c.p.) and exhibit at least 48-fold orientational disorder. Upon cooling both compounds undergo a first-order phase transition at temperatures Tc = 230(5)K (Bu1) and Tc = 250(5)K (Bu2) into monoclinic structures with space group P21/n. The structures at 105 K have a = 17.317 (1), b = 15.598 (1), c = 16.385 (1) Å, γ = 109.477 (4)°, V =4172.7 (8) Å3 and Z = 8 for Bu1 and a = 17.0089(9), b = 15.3159 (8), c = 15.9325 (8) Å, γ = 110.343 (3)°, V= 3891.7 (5) Å3 and Z = 8 for Bu2. The severe disorder of the room-temperature phase is significantly decreased and only a two- or threefold rotational disorder of the molecules remains at 105 K. First-order phase transitions have been observed at pressures of 0.13-0.28 GPa for Bu1 and 0.20-0.24 GPa for Bu2. The high-pressure structures are isostructural to the low-temperature structures. The pressure dependencies of the unit-cell volumes were fitted with Vinet equations of state and the bulk moduli were obtained. At still higher pressures further anomalies in the pressure dependencies of the lattice parameters were observed. These anomalies are explained as additional disorder-order phase transitions.
(Less)
- author
- Wunschel, Markus ; Dinnebier, Robert E. ; Carlson, Stefan LU ; Bernatowicz, Piotr and Van Smaalen, Sander
- organization
- publishing date
- 2003-02
- type
- Contribution to journal
- publication status
- published
- in
- Acta Crystallographica. Section B: Structural Science
- volume
- 59
- issue
- 1
- pages
- 12 pages
- publisher
- Wiley-Blackwell
- external identifiers
-
- scopus:2542497055
- ISSN
- 0108-7681
- DOI
- 10.1107/S0108768102021791
- language
- English
- LU publication?
- yes
- id
- 662c521b-c7e6-4c85-9083-1f4db7f7bfff
- date added to LUP
- 2016-05-04 12:43:35
- date last changed
- 2023-03-23 10:09:05
@article{662c521b-c7e6-4c85-9083-1f4db7f7bfff, abstract = {{<p>The crystal structures of tert-butyl-tris(trimethylsilyl)silane, Si[C(CH<sub>3</sub>)3]<sub>1</sub>[Si(CH<sub>3</sub>)<sub>3</sub>]<sub>3</sub> (Bu1), and di-ferr-butyl-bis(trimethylsilyl)silane, Si[C(CH<sub>3</sub>) <sub>3</sub>]<sub>2</sub>[Si(CH<sub>3</sub>)<sub>3</sub>]<sub>2</sub> (Bu2), at room temperature and at 105 K have been determined by X-ray powder diffraction; the high-pressure behavior for pressures between 0 and 5 GPa is reported. The room-temperature structures have cubic Fm3→m symmetry (Z = 4) with a = 13.2645 (2) Å, V= 2333.87 (4) Å<sup>3</sup> for Bu1 and a = 12.9673 (1) Å, V = 2180.46 (3) Å<sup>3</sup> for Bu2. The molecules are arranged in a cubic close packing (c.c.p.) and exhibit at least 48-fold orientational disorder. Upon cooling both compounds undergo a first-order phase transition at temperatures T<sub>c</sub> = 230(5)K (Bu1) and T<sub>c</sub> = 250(5)K (Bu2) into monoclinic structures with space group P2<sub>1</sub>/n. The structures at 105 K have a = 17.317 (1), b = 15.598 (1), c = 16.385 (1) Å, γ = 109.477 (4)°, V =4172.7 (8) Å<sup>3</sup> and Z = 8 for Bu1 and a = 17.0089(9), b = 15.3159 (8), c = 15.9325 (8) Å, γ = 110.343 (3)°, V= 3891.7 (5) Å<sup>3</sup> and Z = 8 for Bu2. The severe disorder of the room-temperature phase is significantly decreased and only a two- or threefold rotational disorder of the molecules remains at 105 K. First-order phase transitions have been observed at pressures of 0.13-0.28 GPa for Bu1 and 0.20-0.24 GPa for Bu2. The high-pressure structures are isostructural to the low-temperature structures. The pressure dependencies of the unit-cell volumes were fitted with Vinet equations of state and the bulk moduli were obtained. At still higher pressures further anomalies in the pressure dependencies of the lattice parameters were observed. These anomalies are explained as additional disorder-order phase transitions.</p>}}, author = {{Wunschel, Markus and Dinnebier, Robert E. and Carlson, Stefan and Bernatowicz, Piotr and Van Smaalen, Sander}}, issn = {{0108-7681}}, language = {{eng}}, number = {{1}}, pages = {{60--71}}, publisher = {{Wiley-Blackwell}}, series = {{Acta Crystallographica. Section B: Structural Science}}, title = {{Influence of the molecular structures on the high-pressure and low-temperature phase transitions of plastic crystals}}, url = {{http://dx.doi.org/10.1107/S0108768102021791}}, doi = {{10.1107/S0108768102021791}}, volume = {{59}}, year = {{2003}}, }