The reactions of zinc(II) bromide with Schiff bases, 4-(2-hydroxyphenyl)methyleneamino-1,2,4-triazole (HL1) and 4-(2-hydroxy-3-methoxyphenyl)methyleneamino-1,2,4-triazole (HL2), yielded the complexes Zn(HL1)2Br2 (I) and Zn(HL2)2Br2 (II). It was shown that I and II are also formed upon the addition of hydrobromic acid to a suspension of zinc(II) coordination compounds containing anionic L1– and L2– ligands in MeOH. The crystal structures of compounds I and II were determined by single-crystal X-ray diffraction (CIF files CCDC no. 2502710 (I), no. 2502711 (II)). It was found that upon complexation with Zn2+ ions, conformational changes occur in the HL1 and HL2 molecules. This facilitates intramolecular proton transfer, causing compounds I and II to exhibit a photochromic effect, which is confirmed by diffuse reflectance spectroscopy data.
Bovkunova et al. (2025) studied this question.