Polymorphism and Hirshfeld surface analysis of tetraoxa[2]perfluoroarene[2]triazine

Abstract

The title compound, tetraoxa[2]perfluoroarene[2]triazine (C20H6F8N6O6), composed of two tetrafluorophenylene and two triazine moieties connected by four oxygen atoms, was crystallized via slow evaporation of a dichloromethane solution, yielding two polymorphs: block- (I) and plate-shaped (II) crystals. Polymorph I (triclinic, P1, V = 516 Å3 at 173 K) was previously reported by Yang et al. [(2015. Org. Lett. 15, 4414–4417] whereas the newly identified polymorph II (triclinic, P1, V = 1085 Å3 at 100 K) shares the same space group but has a unit-cell volume twice as large, accommodating two symmetrically distinct molecules, Molecule-1 and Molecule-2, with a different molecular arrangement. Since these crystals are expected to exhibit the characteristics of non-porous adaptive crystals, detailed analyses of intermolecular interactions were conducted, revealing that C—F...π-hole interactions are more pronounced in II than in I. Hirshfeld surface analysis at 100 K revealed that the primary contributions to the crystal packing in polymorph I were F...F (17.1%), F...H/H...F (21.5%), C...H/H...C (6.3%), C...F/F...C (4.5%) and C...O/O...C (9.2%) interactions, whereas in polymorph II, these interactions were F...F (9.9% and 10.0%), F...H/H...F (20.9% and 26.5%), C...H/H...C (6.3% and 2.9%), C...F/F...C (8.5% and 10.0%) and C...O/O...C (4.9% and 4.6%) for Molecule-1 and Molecule-2, respectively. Powder X-ray diffraction analysis indicates that polymorph I is the more stable crystalline form, predominantly obtained through rapid precipitation or by grinding the crystals.

Keywords

• crystal structure
• polymorphism
• tetrafluorophenylene
• triazine
• hirshfeld surface analysis