Synthesis, structural and biological studies of two new Co(III) complexes with tridentate hydrazone ligand derived from the antihypertensive drug hydralazine

A new Schiff base derived from the antihypertensive hydralazine (LH) and its Co(III) complexes [CoL2]X*4H2O, where X = NO3− (1) or Cl− (2), were synthesized and characterized using FTIR, UV–Vis, 1H NMR spectroscopy as well as thermal analysis. The crystal structures of the three compounds have been determined using single crystal X-ray diffraction technique. The two complexes structure is strictly divided in a highly ordered part of the [CoL2]+ units and a disordered section containing the anions and sixteen crystal water molecules per unit cell. In the complexes, the two ligand anions (L−) chelate to the Co(III) through the nitrogen atoms in a tridentate meridional manner. The pyridine and phthalazine rings showed deviations from co-planarity in all compounds which attributed to the crystal packing effects as revealed by analysis of their molecular packing using Hirshfeld analysis and further supported by DFT calculations. The optimized structure of the [CoL2]NO3 as a model showed no co-planarity of the two rings while perfectly planar ligand units were predicted in the [CoL2]+ cation indicating that the intermolecular interactions with the nitrate counter anion have a major role in the deviations of the two ring moieties from planarity. The ligand anion (L−) optimized structure using B97D function which include dispersion model showed similar results while the functions (B3LYP and mPW1PW91) which include no dispersion model predicted perfectly planar arrangement. Atoms in molecules (AIM) studies predicted the strength of the Co-N interactions is in the order, Co-N(azomethine) > Co-N(phthalazine) > Co-N(pyridine) which are generally stronger in 2 than 1. The developmental toxicity of LH and its complexes were tested in zebrafish embryos. The ligand itself was very toxic with LC50 of just 2 µM as compared to its metal complexes, whereas, at sub-lethal concentration the ligand perturbed the neurogenesis in zebrafish embryos.