Acid–ammonium heterodimer and N(ammonium)–H...N(pyridine) synthon preference in three salts of nicotinic acid with (1R,2R)‐1,2‐diphenylethylenediamine.

Nicotinic acid (NA), known as vitamin B3, has been widely studied in pharmaceutical science. Herein, three salts derived from NA and (1R,2R)‐1,2‐diphenylethylenediamine (DPEN), including one solvent‐free salt (DPEN)(NA)2 and two solvated salts, (DPEN)(NA)2(EA) and (DPEN)(NA)2(ACN) (EA: ethyl acetate, ACN: acetonitrile), have been obtained and characterized by solid‐state techniques. By the investigation of single‐crystal structures, the synthons, acid–ammonium heterodimer and Nammonium—H...Npyridine between functional groups of 1,2‐diphenylethylenediammonium and NA are revealed and further identified using Hirshfeld surface analysis. The utility of the synthons is further demonstrated by making salts with the NA isomer, isonicotinic acid. Here the synthon occurrences in cocrystals/salts of NA (including NA derivatives) and diamine coformers reported in the Cambridge Structure Database (CSD) are compared. The robustness of acid–ammonium heterodimer and Nammonium—H...Npyridine is investigated by a search of the CSD. The NA salts also show their improved solubility in pH 1.2, 4.5 and 6.8 buffer mediums compared with pure NA material. The crystal structures and solubilities of three nicotinic acid salts with (1R,2R)‐1,2‐diphenylethylenediamine are discussed and an analysis of synthon preference is provided. [ABSTRACT FROM AUTHOR]