Two Crystal Forms of 4′-Methyl-2,4-dinitrodiphenylamine: Polymorphism Governed by Conformational Flexibility of a Supramolecular Synthon

Single crystals of two polymorphic forms of 4 '-methyl-2,4-dinitrodiphenylamine were obtained by crystallization and characterized by X-ray diffraction analysis. One of the forms is non-centrosymmetric (space group P2(1)2(1)2), while the second is centrosymmetric (space group P over bar 1) and contains two crystallographically independent molecules in the asymmetric unit. In both forms, the same supramolecular synthon, a dimer linked by bonding N-H center dot center dot center dot O, O center dot center dot center dot O, and C-H center dot center dot center dot O interactions were found. Despite nearly the same connectivity of the bonding interactions, the conformation of the supramolecular synthon is different, including its unavoidably different symmetry in two polymorphs. The comparison of the crystal packing of the orthorhombic polymorph with that of the related 2,4-dinitrodiphenylamine (space group P2(1)/n) shows the quasi-isostructurality of the fragments, infinite pi-stacks joined by weak non-directional intermolecular interactions. However, the fragments are linked by the supramolecular synthons via either a two-fold axis or an inversion center, which lead to only the partial isostructurality of the crystals.

Automated summary

Single crystals of two polymorphic forms of 4'-methyl-2,4-dinitrodiphenylamine were obtained and characterized. The two forms have different symmetry and contain the same supramolecular synthon. The crystal packing reveals quasi-isostructurality of the fragments joined by weak interactions.