The occurrence of concomitant dimorphism has been observed in the case of trifluoromethyl substituted benzanilide, namely, 3-(trifluoromethy1)-N- 2-( trifluoromethyl) phenyl benz amide, wherein both forms show the presence of a multiple number of molecules in the asymmetric unit (Z' > 1). Thermal studies' confirm the "extremely rare occurrence" of simultaneous melting and solid-to-solid phase transition at the same temperature from centrosymmetric, Z' = 2 structure (triclinic, P (1) over bar, form I) to noncentrosymmetric, Z' = 4 structure (monoclinic, Cc). Both forms exhibit similar density and lattice energy. Conformationally different molecules in the asymmetric unit in both the high-Z' structures are observed to be connected with strong N-H center dot center dot center dot O=-C and weak C-H center dot center dot center dot O=C hydrogen bonds. The dissimilarities in the crystal packing were analyzed by Xpac method, and the molecule molecule interaction energies were evaluated by the PIXEL method. The results revealed the presence of 2D isostructurality between the two forms which mainly consists of the most stabilized intermolecular interactions (namely, strong N-H center dot center dot center dot O=C, and C-H center dot center dot center dot O=C, and C-H center dot center dot center dot pi hydrogen bond's) in their crystal packing while differences in their crystal packing are mainly on account of the presence of weak C-H center dot center dot center dot F-C (sp(3)) hydrogen bond and C(sp(3))-F center dot center dot center dot F-C(sp(3)) interactions.
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