Synthesis, crystal structure, and DFT study of a new Co(II) complex based on 4-[(pyridin-3-yl)diazenyl]morpholine

A new cobalt(II) coordination complex based on the diazenyl ligand 4-[(pyridin-3-yl)diazenyl]morpholine (PDM) has been synthesized and structurally characterized. Single-crystal X-ray diffraction reveals that the Co(II) center adopts a slightly distorted octahedral geometry, coordinated by two monodentate PDM ligands through the pyridine nitrogen atoms, two nitrate anions, and two water molecules, yielding the formulation [Co(PDM)2(NO3)2(H2O)2]. The crystal structure is stabilized by an extended hydrogen-bonding network involving coordinated water molecules and nitrate groups. Density Functional Theory (DFT) calculations were performed using different functionals to benchmark the electronic structure, confirming the quartet spin state as the ground state and showing good agreement with experimental geometrical parameters. Natural Bond Orbital (NBO) analysis highlights significant ligand-to-metal charge transfer, indicating a pronounced covalent character of the Co–ligand interactions. Hirshfeld surface analysis demonstrates that the crystal packing is dominated by H···H and O···H/H···O contacts. Furthermore, molecular docking studies against selected cancer-related protein targets reveal enhanced binding affinities for the cobalt complex compared to the free ligand, suggesting that metal coordination plays a key role in strengthening protein–ligand interactions.