Chudak D. Conductive Radical-Cation Salts of Fulvalens with Complex Metal-Anions

Українська версія

Thesis for the degree of Doctor of Philosophy (PhD)

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  • 102 - Хімія


Specialized Academic Board

ДФ 64.051.042

V.N. Karazin Kharkiv National University


The thesis is devoted to the research of structure and physical properties of radical-cation salts on the basis of tetrathiafulvalene derivatives with bis (dicarbolide) anions, which are synthesized by electrochemical method of radical-cation generation. There is a number of works devoted to the study of RCS with diamagnetic dicarbolide anion Cobalt and its derivatives, in which their structure and conductive properties are analyzed and studied. At the same time, studies with paramagnetic bis (dicarbolides) of iron have not been successful in electrosynthesis. Therefore, one of the tasks was to improve the conditions of electrochemical synthesis of the leading radical-cation salts of tetrathiafulvalene derivatives in order to obtain the corresponding single-crystal samples. As a result, we were able for the first time to obtain new single crystals with halogen-substituted bis (dicarbolide) of Iron (III) Dn[8,8’–Х2–3,3’–Fe(1,2-C2B9H11)2] (where D = BEDT-TTF-bis(ethylenethithio)tetrathiafulvalene, EOTT-4,5-ethylenedithio-4',5'-(2-oxatrimethylenedithio)-tetrathiafulvalene, BPDT-TTF - bis(propylenedithio)-tetrathiafulvalene, X = Cl, Br, I; n = 1,2). Like their structural counterparts, these compounds consist of conductive radical-cation layers having a characteristic β-type packaging and anionic layers. A structural feature of these RCS is the presence in the conductive layer of dimers of the donor molecule, in which there are shortened intermolecular S∙∙∙S contacts. There are also numerous shortened intermolecular S∙∙∙S contacts, both in stacks of dimers of the type "face to face" and between them - of the type "side by side". The study of the electrical conductivity of RCS showed that in a number of salts (BEDT-TTF)x[8,8’–Hal2–3,3’–Fe(1,2-C2B9H11)2]) the conductivity of the radical-cation salt decreases with increasing halogen size. 5, 2 and 1∙10-6 Ohm-1∙cm-1, respectively), which is associated with the "loosening" of the structure. Although shortened intermolecular contacts in the anion – radical-cation (I∙∙∙S) system were found in iodine-derived RCS with bis (ethylenedithio) tetrathiafulvalene, this did not increase its electrical conductivity. The analysis of the obtained RCS in the series (D)2[8,8’–Cl2–3,3’–Fe(1,2-C2B9H11)2]) (where D = BEDT-TTF, EOTT, BPDT-TTF) showed that with the increase of the radical the conformation of the donor molecule changes from almost planar to the conformation of the "chair". Thus, the packing in the middle of the dimers is compacted, as a result of which the distance between the dimers themselves increases and the structure becomes fluffier. Specific resistance studies confirm this effect, and in a number of RCS with BEDT-TTF, EOTT, BPDT-TTF - the electrical conductivity decreases (0.5, 0.2 and 0.05 Ohm-1∙cm-1, respectively). The use of a more planar donor, dibenzotetrathiafulvalene (DB-TTF), has resulted in new DB-TTF RCS with Iron (III) and Chromium (III) bis(dicarbolides). A characteristic feature of the crystal structures of related compounds is the method of overlapping radical-cations in the stack - the long axes of neighboring molecules are rotated relative to each other by ~ 30◦. Electrophysical measurements of these salts have shown that these compounds are semiconductors, and the conductivity of the salt (DB-TTF)2[3,3’-Cr(1,2-C2B9H11)2] is approximately 500 times higher than that of its BEDT-TTF counterpart. This is due to the fact that in the structure (DB-TTF)2[3,3’-Cr(1,2-C2B9H11)2], stacks of radical-cations are regular, while (BEDT-TTF)2[3,3’-Cr(1,2-C2B9H11)2] is characterized by dimeric stacks of radical-cations. Intensive studies of Bechgaard and Fabre salts have shown a wide range of their properties from dielectric to superconducting, in which metal-dielectric transitions occur at low temperatures. Therefore, we synthesized bovine tetramethyltetrahalcogenofulvalenes with metal-carborane anions. As a result of electrophysical measurements it was found that salts of tetramethyltetrathiafulvalene with [3,3’-M(1,2-C2B9H11)2] (M = Fe, Cr) are dielectric, the conductivity of crystals at room temperature is less than 10-10 Ohm-1∙cm-1. In the dissertation work for the first time:(1) RCS with paramagnetic anions of halogen-substituted iron dicarbolides was synthesized by the method of anodic oxidation of π-electron donors, which allowed study of the effect of the magnetic component on the correlation "structure - conductive properties". (2) The influence of the substituent in the anion on the conformation of the dicarbolide ligand and the packing of radical-cations in the conductive layer has been studied. (3) It was found that bulk radicals in the structure of primary tetrathiafulvalene cause "loosening" of the conductive layer, which, in turn, leads to low conductivity. (4) Electrophysical and magnetic properties were determined for the synthesized single crystals, correlations "structure - conductive properties" were studied.


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