Isomorphism in a Series of Five Homologous Compounds

This study examines the relationship between molecular structure and crystal packing in organic crystals of homologous compounds, with an emphasis on isomorphismthe ability of a series of molecules to maintain the same space group and homothetic unit cell when they crystallize despite variations in chemical composition. This phenomenon challenges the conventional view that distinct molecular structures lead to diverse crystalline forms, particularly for chiral molecules, where the interplay between chirality and molecular symmetry within crystal lattices remains poorly understood. Herein, we present the first structurally consistent series of five m-Y-phenyl-N,N-diisopropylglyoxylamide derivatives (Y = H, F, Cl, Br, or I), exemplifying a rare case of isomorphism within a homologous set of achiral molecules in solution that crystallize as conglomerates by adopting a twisted chiral conformation. These enantiomorphic crystals were manually resolved using Pasteur's method, enabling direct investigation of symmetry breaking at the morphological level. Continuous chirality measures quantitatively confirm consistent chiral behavior at both the molecular and crystalline levels, while the unit cell similarity index further validates the isomorphic nature of the series. Thermal analyses reveal systematic trends in stability across the series, while crystallographic studies demonstrate the persistence of packing motifs and supramolecular chirality. Overall, this work introduces a rare class of chiral molecular materials derived from chemically distinct achiral molecules that exhibit isomorphic molecular packing. These systems are broadly relevant to fields ranging from pharmaceuticals to functional materials, where small variations in the solid-state structure can lead to substantial differences in performance.