Supramolecular Diversity, Theoretical Investigation and Antibacterial Activity of Cu, Co and Cd Complexes Based on the Tridentate N,N,O-Schiff Base Ligand Formed In Situ

Abstract

The four new complexes, [Cu(HL1)(L2)Cl] (1), [Cu(HL1)(L1)]∙Cl∙2H2O (2), [Co(L1)2]∙Cl (3) and [Cd(HL1)I2]∙dmso (4), have been prepared by one-pot reactions of the respective chloride or iodide metal salt with a non-aqueous solution of the polydentate Schiff base, HL1, resulted from in situ condensation of benzhydrazide and 2-pyridinecarboxaldehyde, while a ligand HL2, in case of 1, has been formed due to the oxidation of 2-pyridinecarboxaldehyde under reaction conditions. The crystallographic analysis revealed that the molecular building units in 1–4 are linked together into complex structures by hydrogen bonding, resulting in 1D, 2D and 3D supramolecular architectures for 1, 2 and 4, respectively, and the supramolecular trimer for 3. The electronic structures of 1–4 were investigated by the DFT theoretical calculations. The non-covalent interactions in the crystal structures of 1–4 were studied by means of the Hirshfeld surface analysis and the QTAIM theory with a special focus on the C–H⋯Cl bonding. From the DFT/DLPNO-CCSD(T) calculations, using a series of charged model {R3C–H}0⋯Cl− assemblies, we propose linear regressions for assessment of the interaction enthalpy (ΔH, kcal mol−1) and the binding energy (BE, kcal mol−1) between {R3C–H}0 and Cl− sites starting from the electron density at the bond critical point (ρ(rBCP), a.u.): ΔH = −678 × ρ(r) + 3 and BE = −726 × ρ(r) + 4. It was also has been found that compounds 1, 3 and 4 during in vitro screening showed an antibacterial activity toward the nine bacteria species, comprising both Gram-positive and Gram-negative, with MIC values ranging from 156.2 to 625 mg/L. The best results have been obtained against Acinetobacter baumannii MβL.

Keywords

• coordination compounds of Schiff base ligands
• copper complexes
• cobalt complexes
• cadmium complexes
• DFT and DLPNO-CCSD(T) calculations
• QTAIM analysis of electron density