Crystal Structures of Complexes between Hexacyanobutadiene and Tetramethyltetrathiafulvalene and Tetramethylthiotetrathiafulvalene

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Abstract
Hexacyanobutadiene(HCBD) forms two kinds of molecular complexes with tetramethyltetrathiafulvalene(TMTTF) one kind with tetramethylthiotetrathiafulvalene(TTMTTF). The crystal structures of these complexes and neutral TTMTTF are determined by X-ray analyses. (TMTTF)2·HCBD is composed of 2:1 donor and acceptor, and TMTTF exists as a dimer cation stacked along the c axis. HCBD anions are included in the cavity of the dimer stack directing their molecular planes parallel to the stacking axis. TMTTF·HCBD is composed of 1:1 donor and acceptor, and has segregated cation and anion stacks with the interplanar spacing of 3.61 Å in TMTTF and 3.43 Å in HCBD columns. TTMTTF·HCBD is shown to have a regular segregated column with a partial charge transfer. Neutral TTMTTF has a non-planar conformation. The C=C and C–S bond lengths of the donors in free and complexed states are correlated with the degree of the charge transfer in these four complexes, and linear relationships are found between these two quantities.

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