Neutral and Ionic Form of (Benzylthio)Acetic Acid in Novel Aminopyrimidine Based Multi-Component Crystalline Phases

Abstract

(benzylthio)acetic acid (HBTA) and some aminopyrimidines, namely 2-aminopyrimidine (2-AP), 5-aminopyrimidine (5-AP), 2-amino-4,6-dimethylpyrimidine (2-A-4,6-DMP), and 2,4,6-triaminopyrimidine (2,4,6-TAP), were successfully embodied as structural units into the construction of a total of four novel supramolecular organic frameworks. The received crystalline solids were inspected by single-crystal X-ray diffraction (SC XRD) in order to obtain insight into the structural and supramolecular facets. The SOFs deriving from 2-AP, 5-AP, and 2-A-4,6-DMP crystallize in the form of co-crystals (1–3), while the one originating from 2,4,6-TAP crystallizes as a salt solvate (4). The SC XRD results indicated the different contents of structural residues present in the asymmetric units of the crystals 1–4 despite using the same molar ratio of molecular co-former components in each case. The molecular structures of co-crystals 1–3 consist of either one neutral residue of each starting component (1 and 3) or one nonionized residue of the aminopyrimidine ingredient and two neutral residues of the acidic component (2). The asymmetric unit of salt solvate 4 is composed of two ionized residues of each co-former (two 2,4,6-TAP+ cations and two BTA− anions) and one MeOH solvent molecule. The most extensive H-bonding network is observed in the crystal structure of salt solvate 4. The relevant molecular ingredients in co-crystals 1–3 are mainly held together by the neutral Ocarboxylic–H···Npyrimidine and Namine–H···Ocarboxylic H-bonds. In the case of aggregate 4, the corresponding ionic residues are predominantly sustained by the charged-assisted Npyrimidinium–H···Ocarboxylate and Namine–H···Ocarboxylate hydrogen interactions. The MeOH solvent, incorporated into the crystal lattice of adduct 4, is also involved in H-bonding by simultaneously serving as the single donor in OMeOH–H···S and the single acceptor in Namine–H···OMeOH H-bonds, which afforded the structural diversity within the 2,4,6-TAP+ cations and BTA− anions. Other weaker sets of additional non-covalent contacts existing in the crystal structures of analyzed conglomerates are involved in the self-assembly, stabilization, and expansion of total supramolecular organic frameworks. The fact of the formation of non-covalent bonded supramolecular organic frameworks in question is also reflected in corresponding results obtained through elemental analysis (EA), Fourier transform infrared spectroscopy (FT–IR), and thermal analysis (TG/DSC).