The asymmetric unit of the title molecular salt (systematic name: 4-aminoanilinium 5-carboxypentanoate), C 6 H 9 N 2 + ÁC 6 H 9 O 4 À , consists of half a 4-aminobenzenaminium cation (4-ABA) and half a 5-carboxypentanoate anion (5-CP); the other half of each ion is generated by inversion symmetry. Protonation of p-phenylenediamine (PPDA) leads to the formation of a 1:1 salt, but scrutiny of the crystal structure reveals that both of the amine groups of PPDA are partially protonated, with a half-occupied H atom. For the 5-CP anion, an H atom is positioned on an inversion center midway between two O atoms of inversion-related 5-CP ions. In the crystal, the 5-CP anions are linked by the O-HÁ Á ÁO hydrogen bond to form chains propagating along the [110] direction. The chains are linked via N-HÁ Á ÁO and N-HÁ Á ÁN hydrogen bonds involving the 4-ABA cations, forming a three-dimensional supramolecular framework. The title salt was also prepared by mechanochemical synthesis using liquid-assisted grinding (LAG). Its PXRD pattern matches that of the simulated pattern of the crystal structure of the title molecular salt.
Edited by E. V. Boldyreva, Russian Academy of Sciences, Russia Dedicated to Professor N. S. Gajbhiye (IIT, Kanpur) on the occasion of his 65th birthday.
Molecular recognition, is a process where we can design and build supramolecular assemblies of different chemical species with the help of specific non-covalent interactions, like hydrogen bonding, aromatic π•••π stacking, steric repulsion and van der Waals forces.1 Protonation of o-Phenylenediamine (OPDA) with simple organic dicarboxylic acids resulted to produce the molecular crystals of different architectures. The single crystal X-ray diffraction study confirmed the formation of salts of OPDA-Fumarate (OPDFA), [C6H9N2].[C4H4O4] (1), OPDA-malate (OPDMA), [C6H9N2].[C4H5O5] (2) and OPDA-Succinate [C7H4N2O6]•[C3H7NO] (3). All these structures adopted the hetero supramolecular synthons.2 Interestingly, both the protons of fumaric acid is transferred to OPDA to form 1:2 product but one proton each in the cases of malic acid and succinic acid transferred to OPDA to 1:1 product. Compound 1 crystallized in orthorhombic body centred noncentrosymmetric Iba2 space group, Compound 2 crystallised monoclinic centrosymmetric P21/c space group and Compound 3 crystallized in triclinic centrosymmetric P-1 space group with Z' 2.3 The resultant products are also prepared using mechanochemical experimental techniques i.e. liquid assisted grinding / dry co-grinding and the confirmed products are analysed using powder x-ray diffraction and thermal studies.
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