Temperature‐induced pseudopolymorphism of molecular salts from a pyridyl bis‐urea macrocycle and naphthalene‐1,5‐disulfonic acid

• Published in: Acta crystallographica. Section C, Crystal structure communications Vol. 74; no. 1; pp. 75 - 81
• Main Authors: Som, Bozumeh, Shue, Jessica R., Smith, Mark D., Shimizu, Linda S.
• Format: Journal Article
• Language: English
• Published: 5 Abbey Square, Chester, Cheshire CH1 2HU, England International Union of Crystallography 01-01-2018; Wiley Subscription Services, Inc
• Subjects: Acetonitrile; Acids; Chemical bonds; crystal structure; Diketones; Dimethyl sulfoxide; Hydrogen bonding; macrocycle; Materials science; molecular salts; Naphthalene; naphthalenedisulfonic acid; polymorphism; Protons; pyridyl bis‐ureas; Salts; Sulfoxides; Urea; crystal structure; macrocycle; pyridyl bis-ureas; polymorphism; naphthalenedisulfonic acid; molecular salts
• ISSN: 2053-2296; 0108-2701; 2053-2296; 1600-5759
• DOI: 10.1107/S2053229617017600

Molecular salts, often observed as cocrystals, play an important role in the fields of pharmaceutics and materials science, where salt formation is used to tune the properties of active pharmaceutical ingredients (APIs) and improve the stability of solid‐state materials. Salt formation via a proton‐transfer reaction typically alters hydrogen‐bonding motifs and influences supramolecular assembly patterns. We report here the molecular salts formed by the pyridyl bis‐urea macrocycle 3,5,13,15,21,22‐hexaazatricyclo[15.3.1.17,11]docosa‐1(21),7(22),8,10,17,19‐hexaene‐4,14‐dione, (1), and naphthalene‐1,5‐disulfonic acid (H2NDS) as two salt cocrystal solvates, namely 4,14‐dioxo‐3,5,13,15,21,22‐hexaazatricyclo[15.3.1.17,11]docosa‐1(21),7(22),8,10,17,19‐hexaene‐21,22‐diium naphthalene‐1,5‐disulfonate dimethyl sulfoxide disolvate, C16H20N6O22+·C10H6O6S22−·2C2H6OS, (2), and the corresponding monosolvate, C16H20N6O22+·C10H6O6S22−·C2H6OS, (3). This follows the ΔpKa rule such that there is a proton transfer from H2NDS to (1), forming the reported molecular salts through hydrogen bonding. Prior to salt formation, (1) is relatively planar and assembles into columnar structures. The salt cocrystal solvates were obtained upon slow cooling of dimethyl sulfoxide–acetonitrile solutions of the molecular components from two temperatures (363 and 393 K). The proton transfer to (1) significantly alters the conformation of the macrocycle, changing the formerly planar macrocycle into a step‐shaped conformation with trans–cis urea groups in (2) or into a bowl‐shape conformation with trans–trans urea groups in (3).
Molecular salts were formed by proton transfer from naphthalene‐1,5‐disulfonic acid to a pyridyl bis‐urea macrocycle. Two DMSO‐solvated salts displaying two distinct conformations of the macrocycle were obtained upon slow cooling of DMSO–acetonitrile solutions from two temperatures (363 and 393 K).