Triazole-Bridged Zinc Dinuclear Complexes: Mechanochemical Synthesis, Crystal Structure, and Biological Activity.

Two zinc (Zn) complexes, [Zn 2 (DAT) 2 Cl 4 ] ( I ) and [Zn 2 (DAT) 2 (NO 3 ) 4 ] ( II ), were prepared by grinding 3,5-diamino-1,2,4-triazole (C 2 H 5 N 5 , DAT) with Zn precursors such as ZnCl 2 and Zn(NO 3 ) 2 , respectively. This solid-state reaction gives the corresponding Zn complex as the sole product in over 99% yield. This mechanochemical method promotes the selective formation of Zn complexes different from those obtained using the conventional solution-based route. The crystal structures of the two complexes were analyzed by single-crystal X-ray diffraction. Complex ( I ) crystallizes in the monoclinic space group P 2 1 / c , whereas complex ( II ) crystallizes in the triclinic space group P 1̅ . Each complex is characterized by the presence of a characteristic DAT-bridged dimer with one DAT ligand per Zn atom, and the DAT ligand provides a bridge between the two Zn metals. All Zn centers of ( I ) and ( II ) adopted a slightly distorted tetrahedral geometry. Both complexes contain a hexanuclear Zn 2 N 4 ring, but their ring structures are different. Complex ( I ) possesses a boat geometry, while complex ( II ) has a nearly planar structure. The Zn-bound chlorides of complex ( I ) form intermolecular N-H···Cl hydrogen bonds that link neighboring molecules. In complex ( II ), the O atoms in the nitrate groups are hydrogen-bonded to the DAT ligand via O···H-N linkages. Both complexes exhibit blue emissions in the solid state at ambient temperature. They were evaluated as anticancer agents in HeLa, NCCIT, and MCF-7 cancer cell lines, exhibiting promising anticancer activities.