Laboratoire de Chimie de Coordination UPR 8241

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Home > RESEARCH GROUPS > Equipe B

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The "Molecules and Materials" team was created in 1981 by Patrick Cassoux, then led by Lydie Valade (2003-2011). The team was at the source of the preparation of single crystals of many conductors and superconductors derived from coordination complexes but also molecular assemblies combining two physical properties: conductivity, magnetism, conductivity-spin transition, conductivity, photochromism.

Its recent activities include the preparation, the study of physico-chemical properties and the applications of nano-objects of molecular conductors and conductive polymers. We are currently focusing our efforts on systems well-known as single crystals or thin films to highlight any changes in physical characteristics caused by their size reduction.

  • Nanowires of molecular conductors

    We have developed several techniques for preparing nanowires of molecular conductors on nano-structured or functionalized substrates. The CVD technique yielded nanowires of TTF∙TCNQ on austenitic steel or silicon conversion coating [1].

    The dip coating and electrodeposition methods on Si substrate (001) led to nanowires of TTF[Ni(dmit)2]2 and (perylène)2[Au(mnt)2] [1-5] or nanorods of (TMTSF)2ClO4 [6]. TTF[Ni(dmit)2]2 nanowires ( 30 nm diameter) exhibit a transition to a superconducting state at 0.8 K under 7 kbar hydrostatic pressure [7].
    Nanowires of TTF∙TCNQ austenistic steel conversion coating (left) and nanowires of (perylène)2[Au(mnt)2] on nanoporous Si(001) (right)

  • Nanoparticles of molecular conductors

    The synthesis of spherical nanoparticles of molecular conductors is a challenge because of the natural tendency of these compounds to grow as needles for which the growth axis coincides with the stacking of molecules (usually via π - π stacking). We were the first team, at the international level, to obtain (chemically or electrochemically) nanoparticles of molecular conductors built on TTF or BEDT-TTF units. The synthetic strategy is the addition of a "growth regulator" to the medium in which the reaction takes place. The "growth regulator" may be an ionic liquid (imidazolium salt or quaternary ammonium salt), amine or a long chain carboxylic acid or a polymer.

    - Nanoparticles of TTF∙TCNQ (mean diameter ranging from 3 to 50 nm), of TTF[Ni(dmit)2]2 (mean diameter of 40 nm) and of TTFXn or (BEDT-TTF)Xn (0,5 ≤ n ≤ 0,8 et X = Cl, Br) are isolated in presence of [BMIM]X (X = BF4, PF6, N(CF3SO2)2) or [N(CH3)(octyl)3]X (X = Cl, Br) [8-11]. Nanoparticles of TTF[Ni(dmit)2]2 stabilized by [BMIM]BF4 (left) and of (BEDT-TTF)Brn stabilized by [N(CH3)(octyl)3]Br (right)

    These various types of semiconductor nanoparticles are studied as electrode materials in organic field effect transistors (coll. T. Mori, Tokyo [9, 12]) or in organic batteries (coll. T. Sugimoto, Osaka).

    - Semiconducting nanoparticles of TTFXn (0,7 ≤ n ≤ 1 et X = Cl, Br) have been sterically stabilized using a conducting polymer as PEDOT [13].
    PEDOT stabilizer and nanoparticles of TTFBr stabilized in PEDOT

    - Nanoparticles of TTF∙TCNQ were stabilized in organic medium (THF) by octylamine or octanoic acid (mean diameter ranging from 10 to 35 nm). They have a remarkable stability against aggregation and are being tested in electronic devices on satellites (coll. O. Vendier Thales-Alenia-Space et F. Courtade CNES) [14].
    AFM image of nanoparticles of TTF∙TCNQ stabilized by octylamine (mean diameter: 35 nm)

  • Nanoparticles of conducting polymers

    Coordination polymers of [M(C2S4)]nNax type are known since 1975, and show conductivities up to 50 S/cm depending on the nture of the metal M and/or the cation (Na+ or else).
    Nanoparticles of [(NiC2S4)(BMIM)xNay]n.e(BMIM)(BF4)

    Their development and their applications were not successful because of their total insolubility, whatever the solvent. Using the methods described above, we managed to get these polymers in a soluble form, thanks to their nanoparticle stabilized by ionic liquids such as (BMIM)(BF4). Their composition as nanoparticles is [(NiC2S4)(BMIM)xNay]n.e(BMIM)(BF4). Due to the stabilizing layer around the nanoparticles, the electrical conductivities are lower than those of bulk polymers, and are of the order of 10-5 à 10-7 S/cm.

References

[1] Nanowires of molecule-based charge-transfer salts, New Journal of Chemistry, 2007, 31, 519 - 527.

[2] TTF[Ni(dmit)2]2: now as thin films and nanowires, Journal of Solid State Chemistry, 2002, 168, 438 - 443.

[3] A review on molecule-based conductors electrodeposited as thin films, J. Phys.: Condens. Matter., 2008, 20, 184012 (10pp).

[4] New Development in the Preparation of Micro/Nano-Wires of Molecular (Magnetic) Conductors, Materials, 2010, 3, 1640 - 1673.

[5] Nanowires of Molecule-based Charge-Transfer salts in Nanowires/Fundamental Research, A. Hashim (ed.), INTECH (ISBN: 978-953-307-586-0), 2011, 509 - 526.

[6] Evidence of anion-ordering in (TMTSF)2ClO4 electrodeposited on silicon wafers, Synthetic Metals, 2010, 160, 855 - 858.

[7] Superconductivity in TTF[Ni(dmit)2]2 films, European Physics Letters, 2007, 78, 37005/1 - 37005/5.

[8] Ionic liquid stabilized Nanoparticles of Charge-transfer based Conductors, Synthetic Metals, 2010, 160, 1223 - 1227.

[9] Nanoparticles of organic conductors: synthesis and application as electrode material in organic field effect transistors, New Journal of Chemistry, 2011, 35, 1315 - 1319.

[10] Vibrational and optical studies of organic conductor nanoparticles in Vibrational Spectrocopy, D. de Caro (ed.), INTECH (ISBN 978-953-51-0107-9), 2012, 141 - 152.

[11] First TTF-based conductor nanoparticles by electrocrystallization, Synthetic Metals, 2012, 162, 805 - 807.

[12] Charge injection from organic-transfer salts to organic semiconductors, J. Mater. Chem, 2011, 21, 18421 - 18424.

[13] Tetrathiafulvalenium-bromide systems as nanosticks and nanoparticles stabilized by PEDOT, Synthetic Metals, 2011, 161, 1001 - 1004.

[14] Solutions colloïdales de matériaux moléculaires et composites élaborés à partir de ces solutions, Brevet Thales-Alenia-Space/CNES/CNRS FR1001003 (15/09/2011). Extension PCT : 66513WO-ISA220-SES.