Dulce Belo

Gold complexes with dithiothiophene ligands: a metal based on a neutral molecule.

The gold complexes n-Bu4N[Au(alpha-tpdt)2] (5), n-Bu4N[Au(dtpdt)2] (4) and n-Bu4N[Au(tpdt)2] (6) based on new dithiothiophene ligands (alpha-tpdt= 2,3-thiophenedithiolate, dtpdt=2,3-dihydro-5,6-thiophenedithiolate and tpdt = 3,4-thiophenedithiolate) have been prepared and characterised. These gold(III) complexes are diamagnetic, but they can be oxidised with iodine to the paramagnetic compounds [Au(alpha-tpdt)2] (8), [Au(dtpdt)2] (7) and n-Bu4N[[Au(tpdt)2]n-2] (9), which were isolated as fine powders and which exhibit paramagnetic susceptibilities that are almost temperature independent with room temperature values of 2.5 x 10(-4), 2.0 x 10(-4) and 5 x 10(-4) emu x mol(-1), respectively. Interestingly, the neutral complex [Au(alpha-tpdt)2] (8) as a polycrystalline sample displays the properties of a metallic system with a room temperature electrical conductivity of 6 S x cm(-1) and a thermoelectric power of 5.5 microVK(-1); this is the first time that this metallic property has been observed in a molecular system based on a neutral species.

A new hybrid material exhibiting room temperature spin-crossover and ferromagnetic cluster-glass behavior

A new compound, [Fe(5–Cl-qsal)2][Ni(α-tpdt)2].CH3CN, where α-tpdt = 2,3-thiophenedithiolate and H5–Cl-qsal = N-(8-quinolyl)-5-chlorosalicylaldimine, was prepared and structurally and magnetically characterized. The crystal structure is based on an arrangement of alternate layers of [Fe(5–Cl-qsal)2]+ cations and [Ni(α-tpdt)2]− anions. The magnetic measurements and Mossbauer spectroscopy revealed hybrid behavior in this compound, where a ferromagnetic cluster-glass behavior, ascribed to the anions network, and a spin crossover (SCO) of the [Fe(5–Cl-qsal)2]+ cations were observed. The glassy behavior, with a blocking temperature of ca. 7.5 K, results from the disorder in the anionic layer and the competition between ferro- and antiferromagnetic interactions in the anionic layers. The SCO process with T1/2 = 298 K (high spin fraction = γHS = 0.5) is rather sluggish in the limits of the conversion (γHS ∼ 0 and γHS ∼ 1), which is attributed to the effect of the anions that seem to restrict somehow the structural distortions of the cations associated with the SCO process.

Structure and physical properties of (n-Bu4N)2 [Au(dcbdt)2]5

[(n-Bu) 4 N] 2 [Au(dcbdt) 2 ] 5 was obtained as brown thin plate shaped crystals by electrochemical oxidation of (n-Bu) 4 N [Au(dcbdt) 2 ], a Au complex with 4,5-dicyanobenzene-1,2-dithiolate (dcbdt) recently prepared. Cyclic voltammetry and optical spectroscopy studies indicate a mixed valence state. The crystal structure is triclinic and presents slightly pentamerised segregated stacks of the complex along (1,2,0) Single crystal electrical conductivity (σ RT ∼10 S/cm, Ea=13.5 meV) and thermopower measurements (S RT =6μ V/K) suggest a degenerate semiconducting behaviour. The static susceptibility measurements give an almost temperature independent paramagnetic value of 3 5×10 4 emu/mol. These and EPR results are discussed in relation to the crystal structure.

(α-DT-TTF)2[Au(mnt)2]: a weakly disordered molecular spin-ladder system.

The synthesis and characterization of (α-DT-TTF)2[Au(mnt)2] is reported. The magnetic properties of this new salt show that it is still a rare example of an organic spin-ladder. (α-DT-TTF)2[Au(mnt)2] shares the same ladder structure of the DT-TTF and ETT-TTF analogues, and its room temperature conductivity is ∼2 S/cm. Despite the observed donor orientation disorder associated with the thiophenic sulfur atoms, the intermolecular interactions between donor units, calculated using the extended Hückel approximation and a double-ξ basis set, show that the interaction values do not depend on the configuration of the sulfur atom on the thiophenic ring. The insensitivity of the spin-ladder magnetic properties to the donor molecular disorder in (α-DT-TTF)2[Au(mnt)2] is a direct consequence of the negligible contribution of the disordered thiophenic sulfur atom to the HOMO. In the related donor ETT-TTF, this contribution is significant and destroys the magnetic interactions, and no spin-ladder is observed. This compound not only enlarges the number of organic spin-ladder systems in this series of closely related compounds but also provides an interesting example of weakly disordered molecular spin-ladder system.

Conductors based on metal-bisdicyanobenzodithiolate complexes☆

Abstract The physical properties of the partially oxidised complexes [( n -Bu) 4 N] 2 [M(dcbdt) 2 ] 5 with M=Au and Ni (dcbdt=4,5-dicyanobenzene-1,2-dithiolate) are compared and related to the different electronic bandfilling and their slightly different structure. Both compounds present a triclinic structure, space group P- 1, with pentamerised segregated stacks of the complex along [-2 1 0]. The lower electrical conductivity with a larger activation energy, as well as the larger magnitude of thermopower and paramagnetic susceptibility, of the Ni compound are a consequence of both its different electronic bandfilling and more pronounced modulation of the stacking.

Synthesis and characterisation of charge transfer salts based on Au(dcdmp)2 and TTF type donors

The synthesis of the Bu 4 N salt of the Au complex with 2,3-dicyano 5,5-dimercaptopyrazine, Bu 4 N [Au(dcdmp) 2 ], is reported. Charge transfer salts with TTF were obtained by electrocrystallisation and diffusion techniques in acetonitrile. Both techniques afford needle shaped crystals with electrical conductivity of the order of 200 S/cm. 1:1 mixed stack semiconducting compounds were obtained with ET, and one other also semiconducting, with TMTSF.

Ferromagnetism in Charge Transfer Salts Based on Metallocenes and Nickel Bis-Dithiolenes

Abstract The synthesis and preliminary structural and magnetic studies of several compounds based on [M(Cp*)2], with M = Fe; Mn; Cr, and on [Ni(L)2], where L is a 1,2-dithiolate, as bdt = benzenedithiolate, edt = ethylenedithiolate and tcdt = tetrachlorobenzenedithiolate, are reported. In the charge transfer salts, [M(Cp*)2][Ni(L)2], both 1D and layered structures are observed. From the magnetic behavior of the several charge transfer salts apparently ferro and antiferromagnetic interactions are competing in most compounds. Generally AFM interactions dominate at high temperatures, but in several cases FM interactions become dominant at low temperatures. However magnetic ordering was only clearly observed for [Fe(Cp*)2][Ni(edt)2] and [Mn(Cp*)2][Ni(bdt)2], both presenting metamagnetic transitions with TN= 3.2 K and Hc∽ 4 kG, at 2 K, for the first and with TN = 2.3 K and Hc ∽ 200 G, at 2 K, for the second.

Magnetic properties of [Fe(Cp*)2]+ salts of M(dmit)2 and M(dmio)2 (M = Ni, Pd and Pt) anions

Abstract The synthesis and the magnetic properties of decamethylferrocenium salts of the planar radical anions [M(dmix) 2 ] − , where M = Ni, Pd and Pt; and dmix = dmio and dmit, are presented. In this series of charge transfer salts, the magnetic behavior can be dominated by antiferromagnetic (AFM) or ferromagnetic (FM) interactions, depending on the metallic element from the dithiolate complex and on the crystal structure.

Synthesis and magnetic properties of decamethylmetallocenium salts of the monoanionic complex [Ni(tds)2]-

Abstract The synthesis and magnetic properties of [M(Cp*)2][Ni(tds)2], M = Fe. Mn and Cr: tds = bis(trifluoromethyl)ethylenediselenato, are reported. The crystal structure for these compounds consists of an array of parallel stacks of alternating cations, [M(Cp*)2]±, and anions, [Ni(tds)2]−, ··D±A−D±A−D±A−··. For [Fe(Cp*)2][Ni(tds)2] and [Mn(Cp*)2][Ni(tds)2] the magnetic behavior is dominated by FM interactions, with Θ values of 10.6 and 24.6 K respectively, while for [Cr(Cp*)2][Ni(tds)2] the magnetic behavior is dominated by AFM interactions, with Θ = −86.4 K. [Mn(Cp*)2][Ni(tds)2], at low temperatures, shows a metamagnetic behavior. with TN = 2.1 K and HC = 60 G.

Synthesis and characterization of the cyanobenzene-ethylenedithio-TTF donor

Summary A dissymmetric TTF-type electron donor, cyanobenzene-ethylenedithio-tetrathiafulvalene (CNB-EDT-TTF), was obtained in high yield, by a cross-coupling reaction with triethyl phosphite between 2-thioxobenzo[d][1,3]dithiole-5-carbonitrile and 5,6-dihydro-[1,3]dithiolo[4,5-b][1,4]dithiin-2-one. This new donor was characterized namely by single crystal X-ray diffraction, cyclic voltammetry, NMR, UV-visible and IR spectroscopy.