Crystal structures of (E)-2-((2-((pyridin-2-yl)hydrazonyl)methyl)phenolic compounds: different sets of classical hydrogen bonds, X–H···Y (X, Y = O, N)

Structures are reported of (E)-((2-((pyridin-2-yl)hydrazonyl)methyl)arene compounds, 2-aryl-CH=N–CH)-pyridine, 8, namely (aryl=2,4-(HO)2C6H3, 8a; 2,5-(HO)2C6H3, 8b, 2–HOC6H4, 8c, as the hemihydrate, [(8c) 2· (H 2 O )], 2–HO–5–O2NC6H3, 8d; and 2,6-(MeO)2C6H3, 8e. Intramolecular O1–H1··· N2(hydrazonyl) hydrogen bonds are consistantly found in each of the hydroxy compounds, 8a–8d. However, a diverse array of classical intermolecular hydrogen bonds, X–H···Y (X or Y = O or N) are found in 8a–8e. Classical intermolecular hydrogen bonds in 8a are chain forming N3–HN3···O1 and O2–H2···N1(pyridinyl) intermolecular hydrogen bonds, while in the isomer, 8b, dimer forming N3–HN3···N1(pyridinyl) and chain forming O2–H2···O1(pyridinyl) hydrogen bonds are present. The hydrate molecule in [(8c) 2 ·(H 2 O)] is involved in Ow–Hw···N1 intermolecular hydrogen bonding: also present in [(8c) 2 ·(H 2 O)] are chain forming N3–HN3···O2 bonds. The only intermolecular classical hydrogen bonds present in 8d and 8e, are the dimer forming N3–HN3···N1(pyridinyl) bonds. Thus only compounds, 8b, 8d and 8e, exhibit dimer forming N3–HN3···N1(pyridinyl) hydrogen bonds, previously reported fora range of (aryl-CH=N–CH)-pyridine derivatives. The occurence of N3–HN3···N1(pyridinyl) hydrogen bonds in many (aryl-CH=N–CH)-pyridine derivatives demonstrates the importance of such hydrogen bonds. However, as found in 8a and [(8c) 2 ·( H 2 O )], suitable sited donor substituents or the presence of solvate molecules can result in other classical hydrogen bonds being preferred.