π-Bonding between cation-radicals (also referred to as pancake bonding) is a vital factor determining self-assembly and properties of the solid-state associates of the ion-radical salts of planar organic donors. Characterization of such bonding is important for the development of molecular machines and molecular magnets and conductors. Many such applications involve tetrathiafulvalene (TTF) derivatives. Yet, while characteristics of π-bonding of TTF+● itself were reported earlier, the data for its derivatives are lacking. In this work, we present spectral, structural and thermodynamic characteristics of tetramethyltetraselenafulvalene (TMTSeF), tetramethyltetrathiafulvalene (TMTTF), and bis(ethylenedithio)tetrathiafulvalene (which represent most common building block of organic (super)-conductors). To minimize counter-ion interference in the π-bonding, the cation radicals of these organic donors were prepared with weakly-coordinating counter-ions, such as tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, BArF, or closo-dodecamethylcarboranate, CAR. Spectral measurements of the solutions of these cation-radical salts (illustrated in the Figure) in wide range (from 25 °C to –95 °C) of temperatures reveal formation of the dimeric species, e.g., TMTTF+● + TMTTF+● ↔ (TMTTF2)2+. Quantitative treatment of the spectral data afforded thermodynamic characteristics of π-bonding. Crystallization of cation-radical salts allowed to establish structural characteristics of the π-bonded dimers. Experimental characteristics of the dimers are compared with the results of computational analysis of such bonding.

Spectral, structural, and thermodynamic characteristics of π-bonded dimers between cation-radicals of tetrathiafulvalene derivatives

2019 Fall National Meeting

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