Crystal Structures and Physicochemical Properties of 3-Chloro-4-hydroxyphenylacetic Acid Salts with Amines

3-chloro-4-hydroxyphenylacetic acid (CHPAA) is a fungal metabolite. It is a small molecule that is useful in crystal engineering studies due to the functional groups present. Six amines were selected to form salts with CHPAA. Linear derivatives included diethylamine (DEA) and di-N-butylamine (DBM). The aromatic compounds chosen were 2-aminopyridine (A2MP), 2-amino-4-methylpyridine (A24MP), 2-amino-6-methylpyridine (A26MP) and 4-dimethylaminopyridine (DMAP). The salts were characterised using single-crystal X-ray diffraction, thermal analysis, FTIR spectroscopy and Hirshfeld surface analysis. For all the crystal structures, N-HO and C-HCl contacts were present. O-HO contacts were found in all the crystal structures except for (CHPAA(2-))(2DEA(+)), which was also the only structure that displayed a ClCl contact. Furthermore, C-HO contacts were found in all the crystal structures except for (CHPAA(-))(DBM+). The thermal stability trend showed that the DBM salt was more stable than the DEA salt. For the aromatic co-formers, the thermal stability trend showed the following: CHPAA-(DMAP(+)) > (CHPAA(-))(A2MP(+))>(2CHPAA(-)) (2A26MP(+))>(CHPAA(-))(A24MP(+)).

Automated summary

3-chloro-4-hydroxyphenylacetic acid (CHPAA) is a fungal metabolite that is useful in crystal engineering studies. Salts formed with six selected amines were characterized using various techniques, revealing different contact types and thermal stabilities.