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

Abstract

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-H···O and C-H···Cl contacts were present. O-H···O contacts were found in all the crystal structures except for (CHPAA2−)2DEA+, which was also the only structure that displayed a Cl···Cl contact. Furthermore, C-H···O 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+).