The hydroxylic position mediated the luminescent properties based on 4-amino-4H-1,2,4-triazole: Syntheses, crystal structures and Hirshfeld analyses

A set of compounds based on 4-amino-4H-1,2,4-triazole group, namely, x,x'-(4-amino-4H-1,2,4-triazole-3,5-diyl) diphenol [x ​= ​2 (1), x ​= ​3 (2), x ​= ​4 (3)], were obtained through reacting a set of cyano-phenol and hydrazine under the solvothermal conditions, respectively. The title compounds 1–3 have been characterized by IR, element analysis (EA), single crystal X-ray diffraction, and powder X-ray diffraction (PXRD). A lot of hydrogen bonds (C/N/O–H⋯O/N) and C–H … π can be clearly observed in these compounds. It surprisedly occurs the presence of trans- and cis-conformation for compounds 3. The increasing order of the dihedral angles between the phenyl and triazole-yl rings is 1 ​< ​2<3. The solid-state luminescent spectra of 1–3 show that the emission maxima are observed at 461, 414 and 402 ​nm, respectively, which shows the declining order of 1 ​> ​2>3. The luminescent maximal peaks decrease with the diminution of hydroxylic steric effects. The Hirshfeld surface analyses reveal that the contribution order of the O⋯H/H⋯O contacts in compounds 1–3 is listed: 1 ​< ​2<3, which is in a good agreement with that of the dihedral angles, and an inverse proportional to the fluorescent maxima of compounds 1–3.