Crystal engineering with ethynylbenzenes Part 2. Structures of 4-trimethylsilylethynyl-N,N-dimethylaniline, and 4-ethynyl-N,N-dimethylaniline with Z′ = 12 and a single-crystal to single-crystal phase transition at 122.5 ± 2 K

Abstract

The crystal and molecular structures of 4-ethynyl-N,N-dimethylaniline (1), and 4-(trimethylsilylethynyl)-N,N-dimethylaniline (2), have been obtained from X-ray diffraction data. Crystals of 1 exhibit a phase transition at 122.5 ± 2 K. Both polymorphs are triclinic with Z′ = 12, and the molecules are linked into dodecamers by weak hydrogen bonds involving C–H groups. The orthorhombic crystals of 2 show no phase changes and have Z′ = 1.5 (3 half molecules) without short intermolecular contacts.