Coordination Complexes and Polymers of Novel Hybrid Tetrazole-Triazole-Pyrazole Ligands: Synthesis, Structural Characterization, and Biological Evaluation

New series of triazole/pyrazole and tetrazole/triazole/pyrazole ligands were synthesized and coordinated with various transition metals to yield a diverse library of 14 complexes. All compounds were fully characterized by elemental analysis, mass spectrometry, powder X-ray diffractometry, and a range of spectroscopic techniques (¹H NMR, ¹³C NMR, FT-IR, and UV–visible diffuse reflectance). The crystal and molecular structures were elucidated via single-crystal X-ray diffraction, and their supramolecular features were explored through Hirshfeld surface analysis. The ⁵⁷Fe Mössbauer and magnetic SQUID measurements confirmed the high-spin nature of the Fe^II complex 1. In the three human cancer cell lines, most metal complexes are somewhat more cytotoxic than the inactive ligands, with Co(II) complexes 2 and 8 being the most potent in two of the cell lines (with IC₅₀ values in the two-digit micromolar range). Overall, this study highlights how blending tetrazole/triazole/pyrazole ligands with transition metals can lead to coordination compounds with potential in anticancer research, as a proof of concept. These results add valuable insight to the expanding field of metal-based therapeutics and could help guide the development of next-generation, more effective agents.