The First Noncovalent-Bonded Supramolecular Frameworks of (Benzylthio)Acetic Acid with Proline Compounds, Isonicotinamide and Tryptamine

Abstract

The co-crystallization of (benzylthio)acetic acid (HBTA) with L-proline (L-PRO), D-proline (D-PRO), DL-proline (DL-PRO), isonicotinamide (INA) and tryptamine (TPA) led to the formation of five novel crystalline compounds: L-PRO±·HBTA (1), D-PRO±·HBTA (2), DL-PRO±·HBTA (3), INA·HBTA (4) and TPA+·BTA− (5). The prepared supramolecular assemblies were characterized by single crystal X-ray diffraction, an elemental analysis, FT-IR spectroscopy and a thermal analysis based on thermogravimetry (TG) combined with differential scanning calorimetry (DSC). Additionally, their melting points through TG/DSC measurements were established. All fabricated adducts demonstrated the same stoichiometry, displayed as 1:1. The integration of HBTA with selected N-containing co-formers yielded different forms of multi-component crystalline phases: zwitterionic co-crystals (1–3), true co-crystal (4) or true salt (5). In the asymmetric units of 1–4, the acidic ingredient is protonated, whereas the corresponding N-containing entities take either the zwitterionic form (1–3) or remain in the original neutral figure (4). The molecular structure of complex 5 is occupied by the real ionic forms of both components, namely the (benzylthio)acetate anion (BTA−) and the tryptaminium cation (TPA+). In crystals 1–5, the respective molecular residues are permanently bound to each other via strong H-bonds provided by the following pairs of donor···acceptor: Ocarboxylic···Ocarboxylate and Npyrrolidinium···Ocarboxylate in 1–3, Ocarboxylic···Npyridine and Namine···Ocarboxylic in 4 as well as Nindole···Ocarboxylate and Naminium···Ocarboxylate in 5. The crystal structures of conglomerates 1–5 are also stabilized by numerous weaker intermolecular contacts, including C–H···O (1–3, 5), C–H···S (1, 2, 5), C–H···N (5), C–H···C (5), C–H···π (1–5) as well as π···π (4) interactions. The different courses of registered FT-IR spectral traces and thermal profiles for materials 1–5 in relation to their counterparts, gained for the pure molecular ingredients, also clearly confirm the formation of new crystalline phases.