A triazole complex of copper(ii) containing ethylenediamine as a coligand was synthesized using salicylaldehydethiosemicarbazone in the presence of CuCl2. Also, a dinuclear copper(ii) complex was synthesized using the same reagents; however, the order of their addition was different. The structures of these two complexes were characterized via elemental analysis, IR, H-1-NMR, and UV-Vis spectroscopy and mass spectrometry (MS). Furthermore, the molecular structures of complexes I and II were determined via single-crystal X-ray structure analysis. The copper(ii) ion has a distorted square-pyramidal geometry in complex I and a distorted square-planar geometry in complex II. Their fragmentation products were investigated in detail by ESI-MS. Finally, the cytotoxic effects of both complexes were evaluated in MDA-MB-231, MCF-7 and 3T3 fibroblast cell lines via the MTT assay and flow cytometry.