Christophe Faulmann

Infrared and Raman properties of [M(dmit)2] (M=Ni, Pd) based compounds

Abstract The Raman spectra of [M(dmit)2]−n (dmit = 1,3-dithiole-2-thione-4,5-dithiolato, M = Ni, Pd; 0 ≤ n ≤ 2) based complexes with different cations were studied. It was found that the anion Ag modes frequencies correlate linearly with its charge. In the polarized reflectance spectra of the 1:1, [NBu4][Ni(dmit)2] salt the intra- and intermolecular electronic transitions as well as the vibronic bands were assigned. Electron-molecular vibration coupling constants have been evaluated using the dimer model.

A facile route for the preparation of nanoparticles of the spin-crossover complex [Fe(Htrz)2(trz)](BF4) in xerogel transparent composite films

Films and monoliths containing the spin crossover complex [Fe(Htrz)(2)(trz)](BF(4)) (trz = 1,2,4-triazole) as nanoparticles have been obtained. The dispersion and consecutive inclusion of the Fe complex in a silica matrix prepared from tetramethoxysilane or tetraethoxysilane afford monoliths or films with a violet colour at room temperature, which turns white above 380 K. This change of colour is reversible. This thermochromic behaviour has been characterized by measuring the magnetic properties together with thermogravimetric studies and Raman spectroscopy, the result of which all demonstrate that both films and monoliths undergo a spin crossover. Microscopy studies confirm the occurrence of the Fe complex as nanoparticles, in both the monoliths and the films. The facile synthesis of these materials as nanoparticles in transparent films should open the possibility of the synthesis of high quality films.

A chirality-induced alpha phase and a novel molecular magnetic metal in the BEDT-TTF/tris(croconate)ferrate(III) hybrid molecular system

The novel paramagnetic and chiral anion [Fe(C5O5)3]3- has been combined with the organic donor BEDT-TTF (= ET = bis(ethylenedithio)tetrathiafulvalene) to yield the first chirality-induced alpha phase and a paramagnetic metal.

Nanowires of molecule-based charge-transfer salts

Nanowires of molecule-based charge-transfer salts are prepared using two different processing techniques. Isolated [TTF][TCNQ] nanowires are grown by a simple adsorption in organic solution method on stainless steel conversion coatings, used as substrates. They are characterized by Raman spectroscopy and current–voltage measurements. Nanowire films of Per2[Au(mnt)2] and (EDT-TTFVO)4(FeCl4)2 are electrodeposited on (001)-oriented silicon wafers, used as anodes. In the second case, growth as nanowires occurs after functionalizing the Si electrode with a phospholipidic membrane. Electrodeposited nanowire films are studied by various techniques, including electron microscopy, vibrational spectroscopies, X-ray photoelectron spectroscopy and conductivity measurements.

Polymorphism and its effects on the magnetic behaviour of the [Fe(sal2-trien)][Ni(dmit)2] spin-crossover complex

The syntheses, structural characterisation, and magnetic and spectroscopic properties of three new polymorphs of the spin-crossover complex [Fe(sal2-trien)][Ni(dmit)2] are reported. The results are discussed as a function of their intra- and intermolecular arrangement. Correlation of their crystal structures and magnetic properties suggest that some torsion angles play a significant role in the magnetic properties of this class of compounds. Intermolecular contacts are also of importance, and the nature of the short contacts between molecular species seems to be more crucial than their number in the allowance of spin-crossover.

Structure of trans-bis[4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole-N1,N']diaquamanganese(II) dibromide

[Mn(C12H10N6)2(H2O)2]Br2, Mr = 727.28, orthorhombic, Pbca, a = 10.734 (6), b = 17.084 (0), c = 15.182 (6) angstrom, V = 2784 angstrom 3, Z = 4, D(x) = 1.734 g cm-3, lambda-(Mo K-alpha) = 0.71073 angstrom, mu = 33.23 cm-1, F(000) = 1450, T = 295 K, final R = 0.032 for 1493 reflections [I > 2-sigma(I)]. The title compound is the first reported mononuclear compound with the ligand 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole. The manganese ions, situated on an inversion centre, are coordinated by four nitrogen atoms with an N-Mn-N angle of 74.1 (1)-degrees and Mn-N distances of 2.188 (4) and 2.266 (4) angstrom. Two axial water molecules [Mn-O = 2.200 (4) angstrom] complete the coordination sphere of the metal, which is pseudo-octahedral. The two bromide ions are not coordinated but are involved in an extended hydrogen-bridging network with the water ligands and the amino group of the triazole.

Nanoparticles of organic conductors: synthesis and application as electrode material in organic field effect transistors

Stabilization of TTF·TCNQ nanoparticles is studied by varying the ionic liquid nature and solvent medium. The best dispersion is obtained in an acetonitrile/acetone mixture and the smaller size by using [BMIM][BF4], as a stabilizing ionic liquid. Applications of well-dispersed TTF·TCNQ nanoparticles (mean diameter of about 35 nm) as electrode material in organic field-effect transistors are also reported.

Charge injection from organic charge-transfer salts to organic semiconductors

Highly conducting films of organic charge-transfer (CT) salts are fabricated by a solution process from the dispersions stabilized by poly(vinylpyrrolidone). This method provides a general way to obtain conducting films of nonvolatile organic cation- and anion-radical salts with inorganic counter ions. Carrier injection from organic CT salts to organic semiconductors is investigated by using these films as electrodes in organic field-effect transistors. Efficient hole injection is observed not only from organic cation-radical salts but also from anion-radical salts to pentacene and sexithiophene. Electron injection is dominant from both types of CT salts to C60, but hole injection and ambipolar characteristics are observed for cation-radical salts. The Fermi levels of the CT salts are discussed on the basis of these observations.

Tetrathiafulvalene-based conducting deposits on silicon substrates

Tetrathiafulvalene-based molecular conductors, namely [TTF][TCNQ], (TTF)6[N(C2H5)4](HPM12O40) (M = W, Mo), and TTF[Ni(dmit)2]2 have been processed as thin films on microrough (001)-oriented silicon substrates using three different techniques. CVD-grown [TTF][TCNQ] deposits consist of platelets (10 × 5 µm) and filaments (diameter ∼1 µm). CN stretching modes in the infrared spectrum and CC stretching modes in the Raman spectrum are in agreement with a charge transfer of ∼0.6 from the TTF donor to the TCNQ acceptor. The N(1s) photoelectron spectrum confirms the presence of a reduced tetracyanoquinodimethane moiety. The films exhibit a semiconducting behaviour with a room-temperature conductivity of ∼0.4 S cm−1. Deposits of (TTF)6[N(C2H5)4](HPW12O40) are electrodeposited on microrough Si(001) at constant current from TTF and [N(C2H5)4]3(PW12O40) in acetonitrile solution. The films are made of stacked sheets (5 < thickness < 25 µm). Vibrational spectra, conductivity measurements and magnetic susceptibility data are similar to those obtained on single crystals of (TTF)6[N(C2H5)4](HPW12O40) grown on a platinum electrode. Thin films of TTF[Ni(dmit)2]2 are grown on microrough Si(001) by an adsorption process in organic solution. The deposits are characterized by Raman micro-probe and exhibit a pseudo-metallic behaviour with a room-temperature conductivity of about 2 S cm−1.

Synthesis, structure and characterization of mixed cyclopentadienyl–dithiolene metal complexes, [Co(η-C5H5)2][Ni(C3S5)2]3·2MeCN and [Ni(η-C5H5)(C3S5)]

Two new compounds [Co(η-C5H5)2][Ni(C3S5)2]3·2MeCN and [Ni(η-C5H5)(C3S5)], both obtained by combination of the nickel complex anion [Ni(C3S5)2]–(C3S5= 4,5-disulfanyl-1,3-dithiole-2-thionate) and the metallocenium cation [M(η-C5H5)2]+(M = Co or Ni), respectively, have been prepared and characterized crystallographically. The non-integral oxidation-state cobalt complex with the unusual 1 : 3 stoichiometry was obtained by electrochemical oxidation of [NBu4][Ni(C3S5)2] in the presence of [Co(η-C5H5)2]PF6. It is semiconductive (σ= 0.06 S cm–1 at room temperature, Ea= 0.18 eV between 300 and 250 K). The crystal structure shows that the asymmetric unit contains one Ni(C3S5)2 unit, one Ni(C3S5) entity, one Co (η-C5H5) unit and one molecule of acetonitrile. The Ni(C3S5)2 units are associated in triads stacked along the [101] direction. No significant differences are observed in the distances and angles within the two symmetry-unrelated Ni(C3S5)2 units, indicating that the charges of both units are very similar. The cyclopentadienyl rings are staggered due to the location of the Co atoms on inversion centres. The average Co–C distance is comparable to those found in several cobaltocenium salts. The compound [Ni(η-C5H5)(C3S5)] was obtained unexpectedly from the reaction of [Ni(η-C5H5)2]BF4 with Na[Ni(C3S5)2] and characterized by mass spectrometry, conductimetry and X-ray analysis. The crystal structure shows that the asymmetric unit consists of one [Ni(η-C5H5)(C3S5)] entity. The C5H5 ring is disordered over two positions. The Ni(C3S5) unit is planar and almost perpendicular to the C5H5 rings.