Reactions of 2‐(1‐hydrazonoethyl)pyridine with silver salts AgX (X = NO3¯ or ClO4¯) proceeded via the hydrolysis of the pyridine ligand and the formation of the dinuclear [AgL1]2(ClO4)2 (1) and [AgL1(NO3)]2 (2) complexes of the azine ligand, 1,2‐bis(1‐(pyridin‐2‐yl)ethylidene)hydrazine (L1). The structures of the obtained complexes were determined by single crystal X‐ray diffraction. The azine ligand (L1) is acting as a bidentate ligand and connects the two Ag‐sites via the pyridine and the azine nitrogen atoms. In complex 1, the Ag(I) ion is tetra‐coordinated, while in complex 2 the Ag(I) ion is penta‐coordinated due to the presence of additional interaction with one of the oxygen atoms of the nitrate ion. As a result, the azine ligand is significantly twisted in complex 2 compared to complex 1. The optimized geometries of three conformers of L1 were calculated using DFT calculations, and their kinetic and thermodynamic stability were analyzed. It was found that a free rotation of L1 is required prior to the chelation of the Ag(I) ion. The packing in complex 1 is controlled by H…H, O…H, and Ag…O interactions, but in complex 2, the O…H and N…H interactions are the most significant. Complex 2 has better antifungal activity against Aspergillus fumigatus and Candida albicans than the antifungal drug Ketoconazole. Also, the nitrato complex 2 has a promising antioxidant activity compared to the perchlorate complex 1. The cytotoxicity against colon carcinoma HCT‐116 cell line is higher for complex 1 (IC50 = 19.72 ± 0.94 μg/ml) than complex 2 (IC50 = 68.31 ± 2.97 μg/ml).

An unexpected trinuclear Cu(II)–thiazolidine complex has been synthesized by mixing CuCl2·2H2O with the Schiff base ligand, 1-(((4,5-dihydrothiazol-2-yl)ethylidene)hydrazono)methyl)phenol L, in ethanol. Unexpectedly, the reaction proceeded via the hydrolysis of the Schiff base L, followed by cyclization to afford 3-methyl-5,6-dihydrothiazolo[3,2-c][1,2,3]triazole (La), then complexation with the Cu(II) salt, forming the trinuclear [Cu3(La)4(Cl)6] complex. The complex was characterized by means of FTIR spectra, elemental analysis, and X-ray crystallography. In the trinuclear [Cu3(La)4(Cl)6] complex, there are two crystallographically independent hexa- and penta-coordinated Cu(II) sites, where the thiazolidine ligand La units act as a monodentate ligand and a linker between the Cu(II) centers. The crystal packing of the [Cu3(La)4(Cl)6] complex is primarily affected by the weak non-covalent C-H∙∙∙Cl interactions. In accordance with Hirshfeld surface analysis, the Cl∙∙∙H, H∙∙∙H, S∙∙∙H, and N∙∙∙H percentages are 31.9%, 27.2%, 13.5%, and 9.9%, respectively. X-ray photoelectron spectroscopy confirmed the oxidation state of copper as Cu(II), as well as the presence of two different coordination environments around copper centers. The complex showed interesting antibacterial activity against the Gram-positive bacteria S. subtilis, with MIC = 9.7 µg/mL compared to MIC = 4.8 µg/mL for the control, gentamycin. Moreover, the Cu(II) complex showed an equal MIC (312.5 µg/mL) against C. albicans compared to ketoconazole. It also exhibits a very promising inhibitory activity against colon carcinoma (IC50 = 3.75 ± 0.43 µg/mL).