Racemic mimics. Part 6. An example of a double racemic mimic crystallization pathway: 1-phenylethan-1-aminium naphthalene-1-carboxylate in centrosymmetric (P1) and Sohncke (P1) forms

Pseudosymmetry in organic molecular crystals has been an important area of study for decades. One particular type of pseudosymmetry, recently identified by us, is characterized as racemic mimicry. Here, we report the first example of a double racemic mimic crystallization pathway, demonstrated in the organic salt 1-phenylethan-1-aminium naphthalene-1-carboxylate (Ph-1NA). The racemic form, ENOBOZ, crystallizes in the triclinic space group P 1, with Z′ = 2, while the enantiopure form, BIFTIW, crystallizes in P1 with Z′ = 4. The two structures have nearly identical unit cell parameters. Despite their different space group symmetries and chiral compositions, both structures exhibit nearly identical hydrogen-bonded tetrameric motifs (R44 (12) and R42(8)) as well as closely related intermolecular packing arrangements. Analysis of the published structures shows that the two tetramers of ENOBOZ are related by an inversion center, whereas the corresponding clusters in BIFTIW are related by a pseudo-inversion center, with similar conformations of the independent cations in both forms. This pseudosymmetry establishes BIFTIW as a mimic of ENOBOZ, extending the racemic mimic concept to higher Z′ ratios (4:2) for the first time. The discovery of this double racemic mimic in the Cambridge Structural Database highlights the persistence of supramolecular motifs across distinct crystallization pathways and expands our understanding of pseudosymmetry, polymorphism, and the design principles governing supramolecular crystal engineering.