Evaluating the importance of fractional Z′ polymorphs in a trifluoromethylated N,N′-diphenyloxalamide derivative

Abstract

We report a rare incidence of crystal dimorphism in the case of molecule N¹,N²-bis(3-(trifluoromethyl)phenyl)oxalamide which exhibits a variable fractional number of symmetry free molecules (Z′) in the structures. The extensive solution mediated and melt crystallization results in form I (Z′ = 1/2, half molecule) and form II (Z′ = 1/2 + 1/2, two half molecules) polymorphic forms, respectively, and exclusively. A quantitative structural description with the energetics of intermolecular interactions for both polymorphs has been demonstrated thoroughly. The existence of two different molecular conformations and better energetic stabilization of the interaction topology rationalizes the high Z′ structure selection by the molecule in the case of form II.