Thiophenic-TTF derivatives and thiophenic-bisdithiolene complexes for magnetic and conducting materials

June 27, 2017

The synthesis and structural, magnetic and transport properties of several charge transfer salts made by the combination of thiophenic TTF donors with transition metal bisdithiolene complexes obtained by electrocrystallization are described. In this context several TTF-type (TTF=tetrathiafulvalene) donors fused with thiophenic moieties were prepared and explored, namely, DT TTF(dithiophene tetrathiafulvalene), alpha-DT-TTF (alpha-dithiophene-tetrathiafulvalene), alpha-mDT TTF (alpha-methyldithiophene-tetrathiafulvalene) and pre-alpha-mtdt (pre-alpha-methylthiophenetetrathiafulvalenedithiolate). These donor molecules were combined with two different types of transition metal bisdithiolene anionic complexes, maleonitriledithiolate [M(mnt)2] (M=Au, Cu, Co, Pd, Ni and Pt) and 2,3-dicyano-5,6-dimercaptopyrazine [M(dcdmp)2] (M=Au, Cu and Ni). The charge transfer salts were obtained as single crystals by electrocrystallization, and characterized by single crystal X ray diffraction and, as far as possible, also by electrical conductivity, thermopower, magnetic susceptibility and electron paramagnetic resonance (EPR) measurements. With the [M(mnt)2] anions several charge transfer salts were obtained. Amongst these two new spin-ladder systems, (alpha-DT-TTF)2[Au(mnt)2] and (alpha-DT-TTF)2[Au(i-mnt)2], are enlightened as interesting examples of weakly disordered molecular spin ladder systems. In this group of [M(mnt)2] charge transfer salts it is also relevant the low temperature superstructure of the (DT TTF)2[Cu(mnt)2] spin-ladder system which could be solved in small single crystals using synchrotron radiation. The analysis of the low temperatures crystal structure shows that the observed dimerization is due to donor charge ordering, rather than bond ordering, with the spin carriers being associated with fully oxidized donor species alternating with neutral donors. This result enabled not only a correct microscopic description of the spin carrier units but also an understanding of the relative magnitude of the magnetic interactions along the rails and rungs of the ladder. With [M(dcdmp)2] as a π electronic acceptor molecules, which have a more extended π system, due to an inclusion of a pyrazine ring, several new charge transfer salts were obtained. Amongst these it is emphasized the richness of stoichiometries often obtained in the same preparation, as is the case of the compounds (DT TTF)[Cu(dcdmp)2], the ladder like (DT TTF)2[Cu(dcdmp)2] and (DT TTF)3[Cu(dcdmp)2]2. The occurrence of unusual stoichiometries was observed also for (TMTSF)5[Cu(dcdmp)2]4 and the isostructural compounds (TTF)7[Au(dcdmp)2]6 and (TTF)7[Cu(dcdmp)2]6. These last two compounds present room temperature conductivity ranging from 7.7 x 10 3 to 200 S/cm, with a reminiscent metallic behavior for the Cu salt. The pre-alpha-mtdt molecule besides being used as a π-electronic donor, was also used as a ligand precursor for the formation of the extended transition metal bisdithiolenes complexes, [M(alpha-mtdt)2] (M=Au and Ni). These compounds based on a single neutral unit, even though characterized as polycrystalline samples, displayed a rather high room temperature conductivity of 3.2 x 10-1 S/cm and circa 4 S/cm for Au and Ni complex, respectively. These results associated to the thermoelectric and magnetic susceptibility measurements indicate that they are candidates for single component molecular metals.

Authors in the community:

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  R

  Rafaela Antunes Leão da Silva

  ist25577

Supervisors of this institution:

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  M

  Manuel José Duarte Leite de Almeida

  ist21444

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  M

  Maria Dulce Jesus Pombo Belo

  ist171949

101357648

Doutoramento em Química

chemical-sciences - Chemical sciences

eng - English

Instituto Superior Técnico