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A positive to negative uniaxial thermal expansion crossover in an organic benzothienobenzothiophene structure
Author(s) -
Dumitrescu Dan G.,
Roche Gilles H.,
Moreau Joël J. E.,
Dautel Olivier J.,
van der Lee Arie
Publication year - 2020
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520620007702
Subject(s) - benzothiophene , anisotropy , thermal expansion , isotropy , phase transition , tensor (intrinsic definition) , eigenvalues and eigenvectors , negative thermal expansion , phase (matter) , materials science , chemistry , condensed matter physics , crystallography , physics , geometry , mathematics , optics , quantum mechanics , organic chemistry , metallurgy , thiophene
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.