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Decoupling anion-ordering and spin-Peierls transitions in a strongly one-dimensional organic conductor with a chessboard structure, ( o -Me 2 TTF) 2 NO 3 .
- Source :
-
IUCrJ [IUCrJ] 2018 Apr 27; Vol. 5 (Pt 3), pp. 361-372. Date of Electronic Publication: 2018 Apr 27 (Print Publication: 2018). - Publication Year :
- 2018
-
Abstract
- A mixed-valence conducting cation radical salt of the unsymmetrically substituted o -Me <subscript>2</subscript> TTF donor molecule (TTF is tetrathiafulvalene) was obtained upon electrocrystallization in the presence of the non-centrosymmetric NO <subscript>3</subscript> <superscript>-</superscript> anion. It crystallizes at room temperature in the monoclinic P 2 <subscript>1</subscript> / c space group, with the anion disordered on an inversion centre. The donor molecules are stacked along the a axis. A 90° rotation of the longest molecular axis of o -Me <subscript>2</subscript> TTF generates a chessboard-like structure, preventing lateral S⋯S contacts between stacks and providing a strongly one-dimensional electronic system, as confirmed by overlap interaction energies and band structure calculations. A strong dimerization within the stacks explains the semi-conducting behaviour of the salt, with σ <subscript>room temp</subscript> = 3-5 S cm <superscript>-1</superscript> and E <subscript>activated</subscript> = 0.12-0.14 eV. An X-ray diffuse scattering survey of reciprocal space, combined with full structure resolutions at low temperatures (250, 85 and 20 K), evidenced the succession of two structural transitions: a ferroelastic one with an anion-ordering (AO) process and the establishment of a (0, ½, ½) superstructure below 124 (±3) K, also visible via resistivity thermal dependence, followed by a stack tetramerization with the establishment of a (½, ½, ½) superstructure below 90 (±5) K. The latter ground state is driven by a spin-Peierls (SP) instability, as demonstrated by the temperature dependence of the magnetic susceptibility. Surprisingly, these two kinds of instability appear to be fully decoupled here, at variance with other tetra-methyl-tetra-thia-fulvalene (TMTTF) or tetramethyl-tetra-selena-fulvalene (TMTSF) salts with such non-centrosymmetric counter-ions.
Details
- Language :
- English
- ISSN :
- 2052-2525
- Volume :
- 5
- Issue :
- Pt 3
- Database :
- MEDLINE
- Journal :
- IUCrJ
- Publication Type :
- Academic Journal
- Accession number :
- 29755752
- Full Text :
- https://doi.org/10.1107/S2052252518004967