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Influence of the molecular structures on the high-pressure and low-temperature phase transitions of plastic crystals

Wunschel, Markus; Dinnebier, Robert E.; Carlson, Stefan LU ; Bernatowicz, Piotr and Van Smaalen, Sander (2003) In Acta Crystallographica. Section B: Structural Science, Crystal Engineering and Materials 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.

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author
organization
publishing date
type
Contribution to journal
publication status
published
in
Acta Crystallographica. Section B: Structural Science, Crystal Engineering and Materials
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
2016-10-19 09:52:32
@misc{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    = {ARRAY(0x8d3ddf8)},
  series       = {	Acta Crystallographica. Section B: Structural Science, Crystal Engineering and Materials },
  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},
  volume       = {59},
  year         = {2003},
}