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

**Nina Podjed and Barbara Modec \***

Faculty of Chemistry and Chemical Technology, University of Ljubljana, Veˇcna pot 113, 1000 Ljubljana, Slovenia; nina.podjed@fkkt.uni-lj.si

**\*** Correspondence: barbara.modec@fkkt.uni-lj.si

**Abstract:** 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<sup>−</sup> = anion of quinaldinic acid), (2a1bOHH)quin (**2**, 2a1bOHH+ = protonated 2-amino-1-butanol), and (2a2m1pOHH)quin (**3**, 2a2m1pOHH<sup>+</sup> = 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 NH3 <sup>+</sup> moiety and quinaldinate anions with carboxylate moiety. The used amino alcohols contained one OH and one NH2 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 NH3 <sup>+</sup>···−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.

**Keywords:** hydrogen bond; synthon; crystal structure; polymorphism; amino alcohols; quinaldinic acid
