First Nanoparticles of a Conductor Based on the Organic Donor Molecule BETS: κ-(BETS)2FeCl4.

Nanoparticles of the molecular superconductor (BETS)2FeCl4 were obtained by the electrochemical oxidation of BETS in the presence of [(C2H5)4N]FeCl4 and an amphiphilic imine (OATM), acting as a growth controlling agent. When the reaction was carried out with a molar ratio OATM/BETS of 10, roughly spherical nanoparticles exhibiting sizes in the 10-40 nm range were observed. X-ray diffraction patterns evidenced the growth of (BETS)2FeCl4 nanoparticles with the κ-type structure. The current-voltage characteristic recorded on an individual nanoparticle aggregate was fitted with a Shockley diode model. A saturation current of 1216 pA and a threshold voltage of 0.62 V were extracted from this model. This latter value was consistent with roughly half of the energy gap of the semiconducting nano-crystalline aggregate.

Characterization of Charge States in Conducting Organic Nanoparticles by X-ray Photoemission Spectroscopy.

The metallic and semiconducting character of a large family of organic materials based on the electron donor molecule tetrathiafulvalene (TTF) is rooted in the partial oxidation (charge transfer or mixed valency) of TTF derivatives leading to partially filled molecular orbital-based electronic bands. The intrinsic structure of such complexes, with segregated donor and acceptor molecular chains or planes, leads to anisotropic electronic properties (quasi one-dimensional or two-dimensional) and morphology (needle-like or platelet-like crystals). Recently, such materials have been synthesized as nanoparticles by intentionally frustrating the intrinsic anisotropic growth. X-ray photoemission spectroscopy (XPS) has emerged as a valuable technique to characterize the transfer of charge due to its ability to discriminate the different chemical environments or electronic configurations manifested by chemical shifts of core level lines in high-resolution spectra. Since the photoemission process is inherently fast (well below the femtosecond time scale), dynamic processes can be efficiently explored. We determine here the fingerprint of partial oxidation on the photoemission lines of nanoparticles of selected TTF-based conductors.

Possible observation of the signature of the bad metal phase and its crossover to a Fermi liquid in Κ-(BEDT-TTF)2Cu(NCS)2bulk and nanoparticles by Raman scattering.

Κ-(BEDT-TTF)2Cu(NCS)2has been investigated by Raman scattering in both bulk and nanoparticle compounds. Phonon modes from 20 to 1600 cm-1have been assigned. Focusing on the unexplored low frequency phonons, a plateau in frequencies is observed in the bulk phonons between 50 and 100 K and assigned to the signature of the bad metal phase. Nanoparticles of Κ-(BEDT-TTF)2Cu(NCS)2exhibit anomalies at 50 K associated to the crossover from a bad metal to a Fermi liquid whose origins are discussed.

A new compound in the BEDT-TTF family [BEDT-TTF = bis-(ethyl-enedi-thio)-tetra-thia-fulvalene] with a tetra-thio-cyanato-cuprate(II) anion, (BEDT-TTF)4[Cu(NCS)4].

A new phase combining BEDT-TTF and [Cu(NCS)4]2- as the counter-anion, namely bis-[bis(ethyl-enedi-thio)-tetra-thia-fulvalenium] tetra-thio-cyanato-cuprate(II) bis-[bis(ethyl-ene-di-thio)-tetra-thia-fulvalene], (C10H8S8)2[Cu(NCS)4]·2C10H8S8 or (BEDT-TTF)4[Cu(NCS)4] was obtained during a galvanostatic electrocrystallization process. As previously observed with BEDT-TTF-based compounds with oxalatometallate anions, the BEDT-TTF mol-ecules in (BEDT-TTF)4[Cu(NCS)4] exhibit the so-called pseudo-κ arrangement, with two BEDT-TTF mol-ecules being positively charged and two electronically neutral. The bond lengths and angles in the two unique BEDT-TTF mol-ecules differ slightly. The crystal structure consists of layers of BEDT-TTF mol-ecules extending parallel to (001). The width of this layer corresponds to the length of the a axis [16.9036 (17) Å]. The BEDT-TTF layers are separated by layers of centrosymmetric square-planar [Cu(NCS)4]2- dianions.

Colloidal solutions of organic conductive nanoparticles.

Although molecular metals have been known for decades, their insolubility, low vapor pressure, and synthesis routes have prevented them from being integrated into electronic devices. We have prepared stable colloidal solutions of the organic metal TTF-TCNQ that overcome such difficulties. The solutions contain well-dispersed nanoparticles stabilized by long alkyl chain amines. They afford soluble powders by evaporation and homogeneous thin films by drop-casting. Powders and films show room temperature conductivities in the 0.01-0.1 S cm(-1) range.

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.

[Ru(py)4Cl(NO)](PF6)2.0.5H2O: a model system for structural determination and ab initio calculations of photo-induced linkage NO isomers.

Structure analysis of ground state (GS) and two light-induced (SI and SII) metastable linkage NO isomers of [Ru(py)4Cl(NO)](PF6)2.0.5H2O is presented. Illumination of the crystal by a laser with lambda = 473 nm at T = 80 K transfers around 92% of the NO ligands from Ru-N-O into the isomeric configuration Ru-O-N (SI). A subsequent irradiation with lambda = 980 nm generates about 48% of the side-on configuration Ru<(N)(O) (SII). Heating to temperatures above 200 K or irradiation with light in the red spectral range transfers both metastable isomers reversibly back to the GS. Photodifference maps clearly show the N-O configurations for both isomers and they could be used to find a proper starting model for subsequent refinements. Both metastable isomers have slightly but significantly different cell parameters with respect to GS. The main structural changes besides the Ru-O-N and RU<(N)(O) linkage are shortenings of the trans Ru-Cl bonds and the equatorial Ru-N bonds. The experimental results are compared with solid-state calculations based on density functional theory (DFT), which reproduce the observed structures with high accuracy concerning bond lengths and angles. The problem of how the different occupancies of SI and GS could affect refinement results was solved by a simulation procedure using the DFT data as starting values.

Fe2OCl6(2-) salt formed by electrochemical oxidation of ethylenedioxytetrathiafulvalenoquinone-1,3-dithiolemethide in the presence of FeCl4- ion with a silicon wafer electrode.

Electrochemical oxidation of a bent donor molecule, ethylenedioxytetrathiafulvalenoquinone-1,3-dithiolmethide ( 2), in chlorobenzene (PhCl)/ethanol containing NBu 4FeCl 4 as a supporting electrolyte is performed using an undoped silicon wafer electrode. Black crystals of 2 6.Fe 2OCl 6.2PhCl are obtained that have a different molecular formula from that of 2 2.FeCl 4 crystals obtained previously using a platinum rod electrode. The new crystal has a structure composed of alternately stacked layers of 2 molecules and Fe 2OCl 6 (2-) ions, whose Fe-O-Fe bond is completely linear and for which the geometry around the Fe atom is almost tetrahedral. The electrical resistivity decreases with temperature until ca. 200 K, but below this temperature, it gently increases. The magnetic susceptibility (chi p) observed can be described by the sum of chi p obeying a Curie-Weiss law for the impurity spins and of chi p obeying a dimer model with a spin-exchange integral ( J approximately -180 K) in each Fe 2OCl 6 (2-) ion, which is also weakly coupled to neighboring Fe 2OCl 6 (2-) ions through an additional exchange interaction.

Electrical conductivity and spin crossover: a new achievement with a metal bis dithiolene complex.

Three new compounds based on the cationic complex [Fe(III)(3-R-salEen)(2)]+ (salEen stands for N-(2-ethylamino)ethyl)-salicylaldimine, R = H, CH(3)O) with the electroactive Ni(dmit)(2) species as a counterion (dmit stands for 1,3-dithia-2-thione-4,5-dithiolato) have been synthesized and structurally and magnetically characterized. Compound 1 ([Ni(dmit)(2)][Fe(3-OMe-salEen)(2)]. CH(3)OH) shows an apparent hysteresis loop, due to an irreversible desolvatation process. Compound 2 ([Ni(dmit)(2)](NO(3))[Fe(salEen)(2)](2)) exhibits a gradual and incomplete spin transition. Compound 3 ([Ni(dmit)(2)](5)[Fe(salEen)(2)](2), 6CH(3)CN) is a fractional oxidation state complex, which behaves like a semiconductor and exhibits a gradual but complete spin transition between 300 and 4 K.

Photogeneration of two metastable NO linkage isomers with high populations of up to 76% in trans-[RuCl(py)4(NO)][PF6]2.1/2H2O.

Two light-induced metastable NO linkage isomers with oxygen-bound (SI) and side-on configuration (SII) of NO are generated in trans-[RuCl(py)(4)(NO)][PF(6)](2).(1/2)H(2)O. Irradiation by light in the blue-green spectral range (450-530 nm) leads to the population of SI. A further irradiation by near infrared light (920-1100 nm) transfers SI into SII at temperatures below 150 K. The heat release during the thermal decay of the linkage isomers shows that SI and SII are separated from the ground state (GS) by potential barriers of E(A)(SI) = 0.70(3) eV and E(A)(SII) = 0.38(3) eV, and are energetically situated at 1.42(6) eV and 1.07(7) eV above the ground state, respectively. Maximum populations of 76% for SI and of 56% for SII can be generated, as determined by the decrease of the nu(NO) stretching absorption band of the ground state. The nu(NO) stretching vibration shifts to lower energies by 143 cm(-1) in SI and by 300 cm(-1) in SII, indicating that the linkage isomers are of the same type as found in other octahedrally coordinated transition-metal nitrosyl complexes. The experimental observations are in agreement with results from calculations by the density functional theory, which predict that the metastable states correspond to a side-on bonded (SII) and an isonitrosyl (SI) configuration of the NO ligand. The calculations provide the energy minima of the ground state and the metastable states SI and SII as well as the saddle points along the reaction coordinate Q. This reaction coordinate corresponds to a rotation of the NO ligand by about 90 degrees (SII) and 180 degrees (SI), and therefore allows the comparison between observed and calculated activation energies.

Ligand influence on connectivity and processing: magnetic crystals based on metalloceniums and films of TCNE-based magnets (TCNE=tetracyanoethylene).

Molecular materials built from coordination complexes exhibit properties that can be explained through intermolecular electronic interactions driven by the ligand moieties. The nature of the ligand in the precursor molecules governs the connectivity of the magnetic phases and the possibility of producing them by using a gas-phase process. Metallocenium, metal bisdithiolate materials, and solvated and solvent-free [M(tcne)2] (tcne=tetracyanoethylene) magnets illustrate such features.

Metallic polycrystalline thin films of the single-component neutral molecular solid Ni(tmdt)2.

Metallic thin films of the single-component, neutral, molecular solid Ni(tmdt)2 have been prepared by electrocrystallization on passivated silicon substrates. Metallicity is achieved down to 6 K despite the polycrystalline morphology.

[Fe(sal2-trien)][Ni(dmit)2]: towards switchable spin crossover molecular conductors.

A cooperative spin transition behaviour with a wide hysteresis loop (30 K) around 240 K has been observed, for the first time, in a salt based on the redox active [Ni(dmit)(2)](-), anion and the [Fe(sal(2)-trien)](+) spin crossover cation.