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Supramolecular heterosynthon assemblies of ortho-phenylenediamine with substituted aromatic carboxylic acids

Authors :
Risha Mishra
Raghavaiah Pallepogu
Source :
Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials. 74:32-41
Publication Year :
2018
Publisher :
International Union of Crystallography (IUCr), 2018.

Abstract

Co-crystallization experiments conducted between ortho-phenylenediamine (OPDA) and five substituted aromatic acids (phthalic acid, salicylic acid, 4-hydroxybenzoic acid, 4-nitrobenzoic acid and 3,5-dinitrobenzoic acid) reveal the formation of supramolecular networks constructed from acid–base heterosynthons of ortho-phenylenediammonium cations with respective aromatic anions. All of these coformers are generally regarded as safe (GRAS) molecules. The five reported crystal structures are sustained predominantly by intermolecular N+−H...O−, N—H...O− and N—H...O hydrogen-bonding interactions; in addition intramolecular O—H...O and intermolecular O—H...O, O—H...O− and C—H...O interactions contribute to the formation of various networks. Five 1:1 salts [NH2C6H4NH3]+·[COOHC6H4COO]− (1); [NH2C6H4NH3]+·[OHC6H4COO]− (2); [{NH2C6H4NH2}2·{OHC6H4COOH}2·{NH2C6H4NH3}+ 2·{OHC6H4COO}− 2] (OPDPHB) (3); [NH2C6H4NH3]+·[NO2C6H4COO]− (4) and [NH2C6H4NH3]+·[(NO2)2C6H4COO]− (5) were isolated as single crystals by the slow evaporation method and were characterized using spectroscopic and X-ray crystallographic techniques. X-ray diffraction studies confirmed the formation of salts. The pK a difference between the amine and respective acid favours the transfer of a proton from the acid to the amine, which leads to the formation of the anion and the cation. The interactions between these ions resulted in a stable heterosynthon in each case. The asymmetric units of salts (1), (2), (4) and (5) contain one anion and one cation each, but salt (3) consists of two anions, two cations and two neutral species in its asymmetric unit. A polymorph of salt (3) was also isolated from the crystallization of the ground material from liquid-assisted grinding [{NH2C6H4NH2}·{NH2C6H4NH3}+·{OHC6H4COO}−] (OPDPHB 3P). The polymorph crystallized in the monoclinic non-centrosymmetric space group P21. The liquid-assisted grinding experiments using a 1:1 ratio also revealed the formation of the expected salts, except salt (3), where this product matches with polymorph (OPDPHB 3P).

Details

ISSN :
20525206
Volume :
74
Database :
OpenAIRE
Journal :
Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials
Accession number :
edsair.doi...........8ac80fdbe9448e58652e1f01c6d81529