Hydrogen Bonding and Polymorphism of Amino Alcohol Salts with Quinaldinate: Structural Study

Three amino alcohols, 3-amino-1-propanol (abbreviated as 3a1pOH), 2-amino-1-butanol (2a1bOH), and 2-amino-2-methyl-1-propanol (2a2m1pOH), were reacted with quinoline-2-carboxylic acid, known as quinaldinic acid. This combination yielded three salts, (3a1pOHH)quin (1, 3a1pOHH(+) = protonated 3-amino-1-propanol, quin(−) = anion of quinaldinic acid), (2a1bOHH)quin (2, 2a1bOHH(+) = protonated 2-amino-1-butanol), and (2a2m1pOHH)quin (3, 2a2m1pOHH(+) = protonated 2-amino-2-methyl-1-propanol). The 2-amino-1-butanol and 2-amino-2-methyl-1-propanol systems produced two polymorphs each, labeled 2a/2b and 3a/3b, respectively. The compounds were characterized by X-ray structure analysis on single-crystal. The crystal structures of all consisted of protonated amino alcohols with NH(3)(+) moiety and quinaldinate anions with carboxylate moiety. The used amino alcohols contained one OH and one NH(2) functional group, both prone to participate in hydrogen bonding. Therefore, similar connectivity patterns were expected. This proved to be true to some extent as all structures contained the NH(3)(+)∙∙∙(−)OOC heterosynthon. Nevertheless, different hydrogen bonding and π∙∙∙π stacking interactions were observed, leading to distinct connectivity motifs. The largest difference in hydrogen bonding occurred between polymorphs 3a and 3b, as they had only one heterosynton in common.