Multistability in a BEDT-TTF Based Molecular Conductor

Abstract

The low dimensional organic conductor (BEDT-TTF)(2)Br(1.3)I(1.1)Cl(0.6) [BEDT-TTF = bis(ethylenedithio)tertathiafulvalene] is shown to be a unique molecular solid that exists in three crystalline polymorphic forms (alpha'-, alpha' "-, beta' '-phase) and, surprisingly, is able to adopt the same metal-like beta' '-phase at both low (T < 185 K) and high (T > 395 K) temperatures. Several crystals of the alpha'- and alpha' "-phases have been studied using three different techniques: dc-conductivity measurements, ESR spectroscopy, and X-ray diffraction analysis. All these techniques show the existence of the reversible semiconductor <--> metal (alpha' " <--> beta' ') phase transition at both high and low temperatures as well as the alpha' <--> alpha' " phase transition at high temperatures. The phase transitions of these polymorphs are characterized by huge hysteresis and dramatic changes in the transport and magnetic properties. Based on ab initio calculations, it is suggested that dipole-dipole interactions can play a key role in the rich polymorphism of this molecular solid.

Rich Phase Behavior in a Supramolecular Conducting Material Derived from an Organogelator

“…Although single crystal organic conductors show a wide variety of phases, and some phase transformations have been observed, [15,16] the rich phase behavior of the doped TTF-based xerogel reported here is, as far as we know, unprecedented for a molecular material of the characteristics which are derived from a xerogel comprised of nanofibers. This kind of bottom-up hierarchical assembly to what is essentially a non-covalent polymer lends itself to the preparation of this kind of conducting material which may find a number of applications normally reserved for conducting polymer materials.…”

“…[15] As this reaction takes place, TTF-based salts with the different combination of polyiodide entities such as I 3 À (I-I-I) À , [I 3 À Á Á Á I 2 Á Á Á I 3 À ], etc. can crystallize.…”

“…[14] Although some examples of conducting fibers based on iodides of TTF, which shown an ohmic behavior, have been reported, [10][11][12] information concerning their stability, that is one of the most important characteristics of materials for their technical use, is lacking. On the other hand, the well known polymorphism of TTF-based molecular conductors [15,16] raises the question as to how many different phases exist and can be generated in a controlled way in these conducting TTF-based xerogels? Packing differences can lead to varying conducting properties which might pose numerous challenges in seeking applications.…”

A fourth polymorph in the family of BEDT‐TTF salts with thiocyanatocuprate(I) anions: (BEDT‐TTF)4Cu3(NCS)5

“…The (BEDT-TTF) 4 Cu 3 (NCS) 5 phase forms under very similar crystallization conditions as commonly used to prepare k-(BEDT-TTF) 2 Cu(NCS) 2 . While this salt is a semiconductor, it is possible that pressure or thermal treatment could stabilize a metallic state with b 00 -packing as has been observed in (BEDT-TTF) 2 Br 1.3 I 1.1 Cl 0.6 phase [16].…”

Inserting sulfur donor ligands in axial positions of an extended trinickel chain

“…In this work, a sulfur-containing ligand, PhS À , was introduced into the axial positions of an EMAC for the first time. It should be mentioned that there is considerable interest in understanding molecular materials containing sulfur substituents, an example being bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF), because of the potential applications for novel electronic devices such as thermal sensors, switching units, information storage, and processing media [6]. Additionally, the EMAC Ni 3 (dpa) 4 -Cl 2 is known to exhibit single-electron tunneling behavior and the energies of the vibrational states are dependent on the redox state of the molecules [7].…”