Decoupling anion-ordering and spin-Peierls transitions in a strongly one-dimensional organic conductor with a chessboard structure, (o-Me2TTF)2NO3

IUCrJ

Reinheimer, E.W.¹  Foury-Leylekian, P.²  Jeannin, O.³ 

[1]Laboratoire de Physique des Solides, Universit Paris-Saclay, CNRS, Universit Paris-Sud, UMR 8502, Orsay 91405, France

[2]Universit de Rennes, CNRS, IPR (Institut de Physique de Rennes), UMR 6251, Rennes F-35000, France

[3]Universit de Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes), UMR 6226, Rennes F-35000, France

关键词: ANION-ORDERING TRANSITION;    SPIN-PEIERLS TRANSITION;    ORGANIC CONDUCTORS;    MOLECULAR CRYSTALS;    PHASE TRANSITIONS;   

DOI  :  10.1107/S2052252518004967

学科分类：数学（综合）

来源: International Union of Crystallography

【 摘 要 】

A mixed-valence conducting cation radical salt of the unsymmetrically substituted o-Me2TTF donor molecule (TTF is tetrathiafulvalene) was obtained upon electrocrystallization in the presence of the non-centrosymmetric NO3− anion. It crystallizes at room temperature in the monoclinic P21/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-Me2TTF 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 semi­conducting behaviour of the salt, with σroom temp = 3–5 S cm−1 and Eactivated = 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 tetra­methyl­tetra­thia­fulvalene (TMTTF) or tetramethyl­tetra­selena­fulvalene (TMTSF) salts with such non-centrosymmetric counter-ions.

【 授权许可】

CC BY