Polymorphism and Hirshfeld surface analysis of tetra-oxa[2]perfluoro-arene[2]triazine

The title compound, tetra-oxa[2]perfluoro-arene[2]triazine (C₂₀H₆F₈N₆O₆), composed of two tetra-fluoro-phenyl-ene and two triazine moieties connected by four oxygen atoms, was crystallized via slow evaporation of a di-chloro-methane solution, yielding two polymorphs: block- (I) and plate-shaped (II) crystals. Polymorph I (triclinic, P1, V = 516 ų 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 ų at 100 K) shares the same space group but has a unit-cell volume twice as large, accommodating two symmetrically distinct mol-ecules, Mol-ecule-1 and Mol-ecule-2, with a different mol-ecular arrangement. Since these crystals are expected to exhibit the characteristics of non-porous adaptive crystals, detailed analyses of inter-molecular inter-actions were conducted, revealing that C-F⋯π-hole inter-actions 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%) inter-actions, whereas in polymorph II, these inter-actions 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 Mol-ecule-1 and Mol-ecule-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.