A positive to negative uniaxial thermal expansion crossover in an organic benzothienobenzothiophene structure. Issue 4 (22nd July 2020)

• Record Type: Journal Article
• Authors: Dumitrescu, Dan G.; Roche, Gilles H.; Moreau, Joël J. E.; Dautel, Olivier J.; van der Lee, Arie
• Is Part Of: Acta crystallographica. Volume 76:Issue 4(2020:Aug.)
• Page Start: 661
• Page End: 673
• Publication Date: 2020-07-22
• Subjects: isosymmetric phase transition -- thermal expansion -- organic structure
• DOI: 10.1107/S2052520620007702
• Languages: English
• ISSNs: 2052-5206

Abstract

Abstract : A rare transition from positive to negative thermal expansion in an organic herringbone‐stacked structure is reported and related to an isosymmetric phase transition. Abstract : Compound 6, 6′‐([1]benzothieno[3, 2‐ b ][1]benzothiophene‐2, 7‐diyl)bis(butan‐1‐ol) (BTBT‐C4OH ) displays a continuous type 0 first‐order isosymmetric phase transition at 200 K which is accompanied by a continuous change of the thermal expansion along the b axis from positive to negative. The equivalent isotropic atomic displacement parameters for all non‐hydrogen atoms as well as all the eigenvalues of the anisotropic atomic displacement tensor show discontinuous behavior at the phase transition. The eigenvalues of the translational tensor in a rigid‐body description of the molecule are all discontinuous at the phase transition, but the librational eigenvalues are discontinuous only in their temperature derivative. BTBT‐C4OH displays a similar type of quasi‐supercritical phase transition as bis(hydroxyhexyl)[1]benzothieno[3, 2‐ b ][1]benzothiophene (BTBT‐C6OH), despite the difference in molecular packing and the very large difference in thermal expansion magnitudes.