*2.4. Theoretical Calculations*

The theoretical calculations based on density functional theory (DFT) were done with ORCA 4.1 package [24] using B3LYP hybrid functional [25–27] accounting also for relativistic e ffects with ZORA Hamiltonian and respective ZORA-def2-TZVP basis set for Cu, N, O, Cl atoms and ZORA-def2-SVP basis set for C and H atoms [28]. Additionally, the calculations utilized the chain-of-spheres (RIJCOSX) approximation to exact exchange as implemented in ORCA [29,30] and the auxiliary basis SARC/J [31]. Increased integration grids (Grid7 and Gridx7 in ORCA convention), increased radial grid (IntAcc = 8) for Cu atoms and tight Self Consistent Field (SCF) convergence criteria were used in all calculations. The molecular fragment used in the calculations was extracted from the experimental X-ray structure. The calculated spin density was visualized with VESTA 3 program [32].
