https://doi.org/10.1007/s100510170312
Temperature and pressure dependencies of the crystal structure of the organic superconductor (TMTSF)2ClO4
1
Groupe des Sciences Moléculaires (UPR CNRS 9048) , Institut de Chimie de la Matière Condensée de Bordeaux, 33608 Pessac Cedex, France
2
Laboratoire de Physico-Chimie Moléculaire (UMR 5803) , Université Bordeaux I,
33405 Talence Cedex, France
Corresponding author: a chasseau@icmcb.u-bordeaux.fr
Received:
10
April
2000
Revised:
27
September
2000
Published online: 15 February 2001
The crystal structure of (TMTSF)2ClO4 has been determined at (7 K, 1 bar) and at (7 K, 5 kbar) with a high accuracy. For the latter, low temperature and pressure were applied
simultaneously using a X-ray diffraction instrumentation designed in our laboratory, these results
are the first for molecular compounds. The effects of lowering the temperature are not the same
as those produced by increasing the pressure. At (7 K, 1 bar) the anion ordering which occurs in
this compound, and which is characterised by the appearance of superlattice reflections, is
well observed. This anion ordering leads to the presence of two independent stacks of TMTSF
cations which is the only case found in the Bechgaard salts family. The comparison of the low
temperature crystal structures under atmospheric pressure and at 5 kbar shows that the centres of
mass are nearly the same, independent of the pressure: the interchain interactions do not depend
on the doubling of the unit cell. Under pressure, the ordering (0, 1/2, 0) does not occur at any
temperature. These structural data are confirmed by the quantum chemical calculations which
show that the difference in the site energy of the two independent cations is 100 meV.
PACS: 61.50.Ks – Crystallographic aspects of phase transformations; pressure effects / 74.70.Kn – Organic superconductors / 71.15.Fv – Atomic- and molecular-orbital methods (including tight binding approximation, valence-bond method, etc.)
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2001