Аннотация:The copper(II) complex [Cu(H2L1)2(H2O)2] with (2-hydroxyphenyl)phosphonic acid (H3L1) was synthesized. The composition and structure of the complex were determined by X-ray diff raction, elemental analysis, and IR spectroscopy. Quantum chemical calculations of the structure of the H3L1 molecule were performed by the density functional theory (DFT). The protonation constants of H3L1 and the stability constants of its complexes with Cu2+ in water were determined by potentiometric titration. The cytotoxic properties and the accumulation of the [Cu(H2L1)2(H2O)2] complex in human cervical adenocarcinoma HeLa cells were evaluated for the first time, thereby demonstrating that this complex is promising for further biological studies.