14 research outputs found
A unique co-crystallisation motif for bis(4-pyridyl)acetylene involving S---spC interactions with a fused 1,3-dithiole ring
Polymorphism and Superconductivity in Bilayer Molecular Metals (CNB-EDT-TTF)4I3
Electrocrystallization from solutions of the dissymmetrical ET
derivative cyanobenzene-ethylenedithio-tetrathiafulvalene (CNB-EDT-TTF) in the
presence of triiodide I3
− affords two different polymorphs (β″ and κ) with the
composition (CNB-EDT-TTF)4I3, both with a bilayer structure of the donors. These
polymorphs differ in the packing patterns (β″- and κ-type) of the donor molecules in
each layer, in both cases with bifurcated C−N···H interactions effectively coupling
head-to-head donor molecules between layer pairs. Two β″ polymorphs can be
obtained with different degrees of anionic ordering. In one disordered phase, β″d, with
a smaller unit cell, the triiodide anions are disordered over two possible positions in a
channel between the donor bilayers, while in the ordered phase, β″o, the triiodide
anions occupy only one of those positions in this channel, leading to the doubling of
the unit cell in the layer plane. These results for β″ phases contrast with the κ
polymorph previously reported, for which weaker disorder of the triiodide anions, over
two possible orientations with 94 and 6% occupation factors, was observed. While the
β″ polymorphs remains metallic down to 1.5 K with a ρ300K/ρ4K resistivity ratio of 250, the κ polymorph presents a much smaller
resistivity ratio in the range of 4−10 and superconductivity with an onset temperature of 3.5 K.This work was partially supported in Portugal by FCT under
Contracts UID/Multi/04349/2013 and RECI/QEQ-QIN/
0189/2012 and grants to S.O. (SFRH/BD/72722/2010) and
S.R. (SFRH/BPD/113344/2015). Work in Bellaterra was
supported by MINECO-Spain (Grant FIS2015-64886-C5-4-
P) and Generalitat de Catalunya (2014SGR301). E.C.
acknowledges the support of the Spanish MINECO through
the Severo Ochoa Centers of Excellence Program under Grant
SEV-2015-0496.Peer reviewe
DT-TTF Salts with [Cu(dcdmp)2]−: The Richness of Different Stoichiometries
(DT-TTF)[Cu(dcdmp)(2)] (1), (DT-TTF)(2)[Cu(dcdmp)(2)] (2), and (DT-TTF)(3)[Cu(dcdmp)(2)](2) (3) are three new charge transfer salts obtained by electrocrystallization of the donor DT-TTF (dithiophene-tetrathiafulvalene) with the diamagnetic copper complex [Cu(dcdmp)(2)](-) (dcdmp = 2,3-dicyano-5,6-dimercaptopyrazine). Compounds 1 and 3 crystallize in the triclinic system and consist of out-of-registry layers of mixed stacks of donor and acceptor molecules. (DT-TTF)(2)[Cu(dcdmp)(2)] presents a structure similar to the parent spin-ladder systems with donor stacks arranged in pairs; however, a magnetic spin-ladder behavior is not observed probably due to strong interactions between pairs. Compound 3, despite the mixed nature of the stacks, displays relatively high conductivity (7 S/cm) due to a one-dimensional network of interactions between donors.This work was supported by FCT (Portugal) through contracts PTDC/QEQ-SUP/1413/2012 and
UID/Multi/04349/2013 and by DGI, Spain (CTQ2013-40480), the Generalitat de Catalunya
(2014SGR0017), the CIBER de Bioingeniería, Biomateriales y Nanomedicina (CIBER-BBN),
promoted by ISCIII, Spain. R. A. L. S. is thankful to FCT for the PhD grant
SFRH/BD/86131/2012.Peer reviewe
Mossbauer spectroscopy study of the "mysterious" magnetic transition in lambda-(BETS)2FeCl4
The compound lambda-(BETS)2FeCl4 provides an effective demonstration of the
interaction of pi-conduction electron and d-electron localized moment systems
in molecular crystalline materials where antiferromagnetic insulating and
magnetic field induced superconducting states can be realized. The
metal-insulator transition has been thought to be cooperative, involving both
the itinerant pi- electron and localized d-electron spins where
antiferromagnetic order appears in both systems simultaneously. However, recent
specific heat data has indicated otherwise [Akiba et al., J. Phys. Soc. Japan
78,033601(2009)]: although the pi-electron system orders antiferromagnetically
and produces a metal-insulator transition, a "mysterious" paramagnetic
d-electron state remains. We report 57Fe Mossbauer measurements that support
the paramagnetic model, provided the d-electron spins remain in a fast
relaxation state below the transition. From the measured hyperfine fields, we
also determine the temperature dependence of the pi-d electron exchange field.Comment: 10 pages, 3 figures, 1 tabl
Conhecimento, Responsabilidade, Visão e Futuro: bases programáticas da Lista F para o 3.º mandato do Conselho Geral da Universidade de Évora 2016-20
O presente documento inclui o programa de acção e os elementos de campanha da Lista
F, candidata ao 3.º mandato do Conselho Geral da Universidade de Évora (2016-20)
Synthesis and characterization of the cyanobenzene-ethylenedithio-TTF donor
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
A Methyl Substituted Thiophenic-TTF Donor and its Salts
α-Methyldithiophene–tetrathiafulvalene (α-mDT-TTF), the
first alkyl-substituted thiophene–tetrathiafulvalene electronic
donor, and some of its charge-transfer salts were explored.
The crystal structure of α-mDT-TTF is composed of
molecular stacks aligned parallel to each other. Its cyclic voltammetry
shows higher electron-donor ability than the unsubstituted
analogue. This material was employed as a semiconductor
in an organic field-effect transistor and showed a
mobility of 4 10–4 cm2V–1 s–1. Two charge-transfer salts of this donor with [M(mnt)2]– anions (mnt = maleonitriledithiolate),
M = Co and Au, were obtained by electrocrystallization;
they present unusual stoichiometries: (α-mDTTTF)[
Co(mnt)2] and (α-mDT-TTF)3[Au(mnt)2]2. In the cobalt
compound, the donor molecules are fully oxidized and the Co
complex is dimerized; it presents semiconducting behavior
(7 10–3 Scm–1). The gold compound is composed of alternating
stacks of donor trimers and pairs of anions.This work was supported by Portuguese Fundação do Ministério
de Ciência e Tecnologia (FCT) through contract PTDC/QEQ-SUP/
1413/2012, UID/Multi/04349/2013, RECI/QEQ-QIN/0189/2012
and PhD grant SFRH/BD/86131/2012.We also acknowledge financial
support of the European Union (EU) project ERC StG 2012-
306826 e-GAMES and the Networking Research Center of Bioengineering,
Biomaterials and Nanomedicine (CIBER-BBN), the
Spanish Ministerio de Ciencia e Innovación (MICINN), and
Fondos Europeos para el Desarrollo Regional (FEDER) with project
BE-WELL CTQ2013-40480-R and the Generalitat de Catalunya
with project 2014-SGR. We acknowledge the European Synchrotron
Radiation Facility for provision of synchrotron radiation
facilities, and we would like to thank Jonathan Wright for assistance
in using beamline ID11.
[Peer reviewe
Structural relations in (1 : 1) and (2 : 1) cyanobenzene-ethylenedithio-TTF radical salts; the role of CN⋯H interactions
Synthesis and Characterization of Charge Transfer Salts Based on [M(dcdmp)2] (M = Au, Cu and Ni) with TTF Type Donors
The charge transfer salts α-DT-TTF[Au(dcdmp)2] (1), BET-TTF[Au(dcdmp)2] (2M and 2T), α-DT-TTF[Cu(dcdmp)2] (3), ET[Cu(dcdmp)2] (4), (BET-TTF)2[Cu(dcdmp)2] (5), (ET)2[Ni(dcdmp)2] (6), and α-mtdt[Cu(dcdmp)2] (7) were obtained by electrocrystallization of different electron donor molecules derived from TTF (α-DT-TTF = alpha-dithiophene-tetrathiafulvalene; BET-TTF = (bis(ethylenethio)tetrathiafulvalene; ET = bis(ethylenedithio)-tetrathiafulvalene; α-mtdt = alpha-methylthiophenetetrathiafulvalene) in the presence of transition metal complex [M(dcdmp)2] (M = Au (III), Cu (III) and Ni (II)) (dcdmp = 2,3-dicyano-5,6-dimercaptopyrazine). Compounds 1 and 2 (2M and 2T) have a similar packing pattern composed of mixed stacks of alternating donor-acceptor molecules. For (BET-TTF)[Au(dcdmp)2] two different crystal structures (2M and 2T) were obtained indicating polymorphism. Compounds 3 and 4 are isostructural being composed of zigzag chains of alternating donor and acceptor molecules. The salts with a 2:1 stoichiometry, (BET-TTF)2[Cu(dcdmp)2] (5), and (ET)2[Ni(dcdmp)2] (6) present the donor molecules fully oxidized and [M(dcdmp)2] (M = Ni and Cu) in a dianionic state. The salt of the dissymmetric donor α-mtdt with [Cu(dcdmp)2], α-mtdt[Cu(dcdmp)2] (7) has a crystal structure composed of segregated donor stacks that are positioned in a head-to-head fashion and alternate with the anion stacks. All charge transfer salts (1–7) are modest semiconductors with conductivities in the range 10−1–10−5 S/cm, with the highest values obtained in α-DT-TTF salts, compounds 1 and 3