Sandra Rabaça

Mossbauer spectroscopy study of the "mysterious" magnetic transition in λ − (BET S)2F eCl4

The compound � − (BETS)2FeCl4 provides an effective demonstration of the interaction of � 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 �- 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 �-electron system orders antiferromagnetically and produces a metal-insulator transition, a “mysterious” paramagnetic d-electron state remains.

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.

Metamagnetism in linear chain electron-transfer salts based on decamethylferrocenium and metal–bis(dichalcogenate) acceptors

Abstract The crystal structure of the electron-transfer (ET) salts [Fe(Cp*)2][M(tds)2], with M=Ni (1) and Pt (2), consists of an array of parallel alternating donors, [Fe(Cp*)2] +, and acceptors, [M(tds)2] −, ⋯DADADA⋯, stacks. For T>20 K, the magnetic susceptibility follows a Curie–Weiss behavior, with θ values of 8.9 and 9.3 K for 1 and 2, respectively. A metamagnetic behavior was observed in 2, with TN=3.3 K and HC=3.95 kG at 1.7 K, resulting from a high magnetic anisotropy. A systematic study of the intra and interchain magnetic interactions was performed on 1, 2 and other ET salts based on decamethylferrocenium and on metal–bis(dichalcogenate) acceptors, with a similar crystal structure. The observed magnetic behavior of these compounds is consistent with the presence of strong ferromagnetic intrachain DA interactions and weaker antiferromagnetic interchain interactions, predicted by the McConnell I model. A variety of interionic interchain contacts were found in these ET salts (AA, DD and DA) and these contacts were observed to give rise to antiferromagnetic interchain coupling. Although it was only observed in the case of 2 and [Fe(Cp*)2][Ni(edt)2], metamagnetism is expected to occur at lower temperatures in the other ET salts due to weaker intra and interchain coupling.

[Fe(qdt)2]− salts; an undimerised FeIII bisdithiolene complex stabilised by cation interactions

(n-Bu)4N[Fe(qdt)2] provides the first example of an undimerised FeIII bisdithiolene complex with well isolated square planar coordinated [Fe(qdt)2]− units, due to short apical Fe⋯H, Fe⋯C and S⋯H contacts with the cations, while the tetraphenylarsonium salt of this complex presents the usual dimerisation as [Fe(qdt)2]22−, with square-based pyramidal coordination of Fe.

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.

Bilayer Molecular Metals Based on Dissymmetrical Electron Donors

The electrocrystallization from solutions of cyanobenzene-ethylenedithio-tetrathiafulvalene (CNB-EDT-TTF) in the presence of different anions X = ClO4(-), PF6(-), and I3(-), affords a new type of 2D molecular metals with composition (CNB-EDT-TTF)4X based on an unprecedented bilayer structure of the donors induced by effective head to head interdonor interactions through the nitrile groups, which is responsible for 2D metallic systems with unusual properties such as the higher band filling, larger effective mass of carriers, and almost degenerated double Fermi surfaces.

Synthesis, structural and magnetic characterization of the metamagnet [Fe(C5Me5)2]DMe–DCNQI

The addition of a solution of decamethylferrocene, [Fe(Cp*) 2 ], to a solution containing N,N′-dicyano-2,5-dimethyl-1,4-benzoquinonediimine, DMe–DCNQI, results in the formation of the electron-transfer salt [Fe(Cp*) 2 ]DMe–DCNQI. A single crystal X-ray structure determination showed that this compound belongs to the triclinic space group P 1, with a =8.6665(6) A, b =9.5552(5) A, c =9.8392(5) A, α =101.421(5)°, β =112.523(5)°, γ =106.639(6)°, Z =1, R 1 =0.0536, wR 2 =0.1499. The solid state structure consists of an array of parallel alternating donors, [Fe(Cp*) 2 ] + , and acceptors, DMe–DCNQI − , ⋯DADADA⋯ stacks along [111]. At high temperatures ( T >20 K), the magnetic susceptibility obeys to the Curie–Weiss expression, with a θ value of 3.2 K, revealing the existence of dominant FM interactions. At low temperatures a metamagnetic behavior was observed for [Fe(Cp*) 2 ]DMe–DCNQI, with T N =3.9 K and H C =5.5 kG at 1.7 K, resulting from a high magnetic anisotropy, due to the coexistence of strong FM DA intrachain interactions and weaker AFM (DD and AA) interchain interactions.

Crystal structure of (RBzPy)n[Ni(4-pedt)2] salts engineering by pyridine ring arrangements

Two new salts (p-NO2BzPy)2 [Ni(4-pedt)2] and p-BrBzPy [Ni(4-pedt)2] [BzPy=benzylpyridinium, 4-pedt = 1-(pyridine-4-yl)- ethylene-1,2-dithiolate] were prepared and characterized by X-ray diffraction and magnetic measurements. The paramagnetic salt p-BrBzPy [Ni(4-pedt)2] displays strong pair antiferromagnetic interactions.