Solid-state fluorescent 1,2,4-triazole zinc(II) complexes: Self-organization via bifurcated (N[sbnd]H)₂⋯Cl contacts

Five bis-triazole zinc(II) chloride complexes exhibiting solid-state fluorescence were prepared in 58–99% isolated yields and fully characterized by HRESI-MS, IR, ¹H- and CP-MAS TOSS ¹³C{¹H} NMR. Results of single-crystal XRD indicate that their crystal structures include the rare bifurcated N[sbnd]H⋯Cl noncovalent contacts. The estimated energy of these interactions is 1.3–1.9 kcal/mol (5.2–7.6 kcal/mol per each associate) as verified by DFT calculations at the ωB97XD/6-31G(d) level of theory and by QTAIM method. The complexes exhibit emission maxima in the range 372–422 nm and nanosecond lifetimes of the fluorescence. In the case of the 3-pheny-1-dimethylamino-1,2,4-triazole complex, a significant enhancement of quantum yield (ca. 20-fold) and blue shift of the emission maximum (33 nm) were observed relatively to the uncomplexed 1,2,4-triazole.