Wechselwirkungen in Molekülkristallen, 127 [1] Die unterschiedlichen Strukturen des im Kristall verdrillten 1,4-Bis(tricyanvinyl)- benzols sowie des eingeebneten 1-Tricyanvinylbenzols, Dichtefunktional- Berechnungen und cyclovoltammetrisch sowie ESR/ENDOR-spektroskopisch charakterisiertes Reduktionsverhalten / Interactions in Molecular Crystals, 127 [1]The Different Structures in the Crystal of Twisted 1,4-Bis(tricyanovinyl)benzene as well as of Planar 1-Tricyanovinyl-benzene, Density Functional Calculations and Reduction Behaviour Studied by Cyclovoltammetry and ESR/ENDOR Spectroscopy

The attempted crystal growth of 1,4-bis(tricyanovinyl)benzene dianion salts, although without success so far, has provided information of general interest. The crystal structures of the related mono and 1,4-bis(tricyanovinyl)benzene derivatives differ considerably in their substituent group twisting angles: The two tricyanovinylbenzenes in split-positions exhibit dihedral angles of only 6° or 11°, whereas the two C2(CN)3 groups of the disubstituted benzene are conrotationally twisted by 48° out of the benzene plane. Density functional calculations with 6 - 311++G** basis sets, however, predict identical values of 32° for both compounds and, therefore, their crystal arrangements are discussed in detail for packingenforced additional interactions. Cyclovoltammetric and ESR/ENDOR-measurements provide information on the redox behaviour, a prerequisite for attempts to crystallize molecular anion salts: The 1,4-disubstituted derivative with a cyclovoltammetrically determined halfwave reduction potential of +.14 V in aprotic THF solution proves to be one of the strongest polycyano-substituted π-acceptors and its radical anion can be selectively generated by T1 metal reduction as confirmed by its ESR/ENDOR spectra.