Synthesis, Structure, and Magnetic and Biological Properties of Copper(II) Complexes with 1,3,4-Thiadiazole Derivatives

New coordination compounds of copper(II) with 2,5-bis(ethylthio)-1,3,4-thiadiazole (L(1)) and 2,5-bis(pyridylmethylthio)-1,3,4-thiadiazole (L(2)) with compositions Cu(L(1))(2)Br(2), Cu(L(1))(C(2)N(3))(2), Cu(L(2))Cl(2), and Cu(L(2))Br(2) were prepared. The complexes were identified and studied by CHN analysis, infrared (IR) spectroscopy, powder X-Ray diffraction (XRD), and static magnetic susceptibility. The crystal structures of Cu(II) complexes with L(1) were determined. The structures of the coordination core of complexes Cu(L(2))Cl(2) and Cu(L(2))Br(2) were determined by Extended X-ray absorption fine structure (EXAFS) spectroscopy. Magnetization measurements have revealed various magnetic states in the studied complexes, ranging from an almost ideal paramagnet in Cu(L(1))(2)Br(2) to alternating-exchange antiferromagnetic chains in Cu(L(1))(C(2)N(3))(2), where double dicyanamide bridges provide an unusually strong exchange interaction (J(1)/k(B) ≈ −23.5 K; J(2)/k(B) ≈ −20.2 K) between Cu(II) ions. The cytotoxic activity of copper(II) complexes with L(2) was estimated on the human cell lines of breast adenocarcinoma (MCF-7) and hepatocellular carcinoma (HepG2).