Syntheses, Crystal Structures, Transport Properties and First-Principles Electronic Structure Study of the (tTTF)₂X (X = Br, I) Low-Dimensional Antiferromagnets

Abstract

An efficient synthetic procedure for the preparation of unsymmetrically substituted tetrathiafulvalene (TTF) donors has been used to obtain the trimethylene-tetrathiafulvalene (tTTF) donor with high purity. Good quality crystals of the two (tTTF)(2)X (X = Br, I) salts have been obtained by electrocrystallization. The two salts are isomorphous and contain tTTF layers which are built from (tTTF)(2) dimeric units. Both systems are low-dimensional antiferromagnets with the highest Néel temperatures for TTF based radical cation salts: ≈ 35 K (Br salt) and ≈43 K (I salt). The resistivity is found to substantially decrease with pressure although both salts still have activated conductivity at 25 kbar. First-principles Density Functional Theory (DFT) calculations have been used to investigate the relative strength of the three different types of magnetic interactions in the tTTF layers as well as the potential magnetic ground states. These calculations successfully predict the nature of the ground state and suggest a possible correlation between structural details and Néel temperatures for the bromine and iodine salts. Remarkably, the calculated antiferromagnetic ground state can be predicted from the nesting properties of the Fermi surface for the hypothetical Pauli paramagnetic metallic state.

Infrared and Raman spectroscopic studies of the charge localization in one‐dimensional organic metals (DMtTTF)2X (X = ReO4, ClO4) with regular organic stacks

“…Following this route, DMtTTF was prepared in pure form and in 53% yield, without need for tedious chromatographic separations, from 4,5-dimethyl-1, 3-dithiolium iodide and trimethylene-2-piperidyl-1,3-dithiolium hexafluorophosphate. [33,34] The electrocrystallizations of DMtTTF in 1,1,2-trichloroethane with the ClO 4 -and ReO 4 -anions afforded the 2 : 1 phases described earlier, [6,7] which crystallize in the monoclinic system, space group C2/c. As shown in Fig.…”

“…Both starting materials are stable in the reaction conditions and do not afford any symmetrical TTFs. Following this route, DMtTTF was prepared in pure form and in 53% yield, without need for tedious chromatographic separations, from 4,5‐dimethyl‐1,3‐dithiolium iodide and trimethylene‐2‐piperidyl‐1,3‐dithiolium hexafluorophosphate …”

Exploring the Electronic Structure of an Organic Semiconductor Based on a Compactly Fused Electron Donor–Acceptor Molecule

“…We did not repeat the calculations for the solid, but instead we carried out calculations for selected dimers representative of the intra‐ and interstack interactions. We found that the intrastack interaction is strongly antiferromagnetic for an organic system,12 ( J =−213 cm −1 ), whereas all interstack interactions are extremely small (<0.1 cm −1 ). These calculations thus confirm that the system is in fact a 1D system with strong AF interactions between dimers within the π stacks and weak interstack interactions.…”

Charge localization in 1D tetramerized organic conductors: the special case of (tTTF)2ClO4

“…The high-purity donor molecule tTTF was synthesized according to our original procedure described previously for the preparation of (tTTF)2X (X = Cl, Br, I) halide salts [18].…”