Halogen Bonding in Diaza-Triisopropylsilyl-Tetracene Crystals?

Four halogenated triisopropylsilylethynyl (TIPS)-tetracene derivatives were synthesized, their single crystal structures and optical and electronic properties were examined. Both, diiodo-TIPS-diazatetracene and dibromo-TIPS-diazatetracene showed herringbone arrangements, in which the halogen atoms are directed toward the nitrogen atoms of a neighboring molecule with slightly lower distances than the van der Waals radii between halogen and nitrogen atoms. Computations of the electrostatic potentials showed the availability and the strength of σ holes, so that we assume a weak halogen–nitrogen bonding. Tribromo-TIPS-diazatetracene delivered a 2D-brick wall structure with no sign of a halogen bonding. Dibromo-TIPS-tetracene crystallized neither in a herringbone nor in a brick wall motif. These results show that for halogenated azaacenes at least weak halogen–nitrogen interactions exist.