Discovery of a New System Exhibiting Abundant Polymorphism:m-Aminobenzoic Acid

Abstract

Given the importance of the phenomenon of polymorphism from both fundamental and applied perspectives, there is considerable interest in the discovery of new systems that exhibit abundant polymorphism. In the present article, the preparation strategies and structural properties of three new polymorphs (denoted Forms III, IV, and V) of m-aminobenzoic acid (m-ABA) are reported, elevating this system to the rare class of polymorphic systems with at least five known polymorphs. The crystal structures of the three new polymorphs have been determined directly from powder X-ray diffraction data, using the direct-space genetic algorithm technique for structure solution followed by Rietveld refinement, demonstrating the opportunities that now exist for determining crystal structures when crystals of sufficient size and quality for single-crystal X-ray diffraction are not available. In two of the new polymorphs (Forms III and IV), the m-ABA molecules exist in the zwitterionic form (as in the previously known Form I), while the m-ABA molecules in the other new polymorph (Form V) are nonzwitterionic (as in the previously known Form II). Furthermore, disorder of the molecular orientation, and hence disorder in the intermolecular hydrogen-bonding arrangement, is revealed in Form V. The assignment of the tautomeric form in each polymorph is confirmed by X-ray photoelectron spectroscopy. Issues relating to the relative stabilities of the five polymorphs of m-ABA are discussed.

Boron–Nitrogen‐Doped Nanographenes: A Synthetic Tale from Borazine Precursors

“…Structure solution of 1 was carried out using the directspace strategy, [52,53] implemented by using ag enetica lgorithm (GA) in the program EAGER. [54][55][56][57][58][59][60][61] In the direct-spaces tructure solution calculations( see Supporting Information for more details), the molecular model wasd erived from the molecule in the crystal structure [49] of the carbon analogue of 1,b ut with the central C 6 ring replaced by ac entral B 3 N 3 ring. The asymmetricu nit comprised the whole moleculeo f1 with half occupancy of all atoms, and with the center of the molecule fixed at ac rystallographic inversion center.C learly,t he inversion symmetry operation creates disorder in the positions of the B and Na toms in the central ring, resulting in an occupancy of B 0.5 N 0.5 for each atomics ite in the central ring.…”

“CLASSIC NMR”: An In‐Situ NMR Strategy for Mapping the Time‐Evolution of Crystallization Processes by Combined Liquid‐State and Solid‐State Measurements

“…Here we demonstrate the advantages of the CLASSIC NMR strategy by applying it to study crystallization of m ‐aminobenzoic acid ( m ‐ABA), a system of interest in the context of polymorphism research 5. To date, five polymorphs of m ‐ABA have been reported 5a,b. The crystal structures of four polymorphs (Forms II, III, IV, and V) are known, while the crystal structure of Form I has not yet been determined.…”

Solvation and Aggregation of Meta-aminobenzoic Acid in Water: Density Functional Theory and Molecular Dynamics Study

“…1 This molecules also represents a fascinating model system for polymorphic research because it can crystallize in five different crystal structures (I-V). 2 The very strong polymorphic character of metaaminobenzoic acid can be related to the manifold of inter-molecular interactions between metaaminobenzoic acid molecules (hydrogen (H) bonding, π-π interactions and H-π interactions) but also to the ability of this molecule to exist in either of both the nonionic (mABA) and zwitterionic (mABA ± ) forms ( Figure 1). 3 In fact, in the polymorphs denoted I, III and V the meta-aminobenzoic acid molecules are zwitterionic, and in the polymorphs II and V they are nonionic.…”