Two Hg(II) complexes of 4-pyridinecarbacylamidophosphates: Synthesis, crystal structures, theoretical studies and in vitro antibacterial evaluation

Abstract

Two new Hg(II) complexes of 4-pyridinecarbacylamidophosphate ligands, HgCl2(L1)2C1 (L1 = 4-NC5H4C(O)NHP(O)[NHC(CH3)3]2); [Hg(L2)Cl3]−[(L2)H]+C2 (L2 = 4-NC5H4C(O)NHP(O)[NHC5H9]2) were synthesized and characterized on the basis of elemental analysis, IR, UV–Vis, and multinuclear NMR spectroscopy. Molecular structures of C1 and C2 were determined by X-ray crystallography and revealed that coordination of ligands to Hg(II) has occurred from the nitrogen atom of the pyridine ring in neutral (C1) and ionic (C2) metal complexes. Coordination of L1 and L2 from Npyridine, as a monodentate ligand, resulted in infinite 1D and 2D hydrogen-bonded polymeric chains for C1 and C2, respectively. Mass spectral data further support the structure of the compounds and XRD indicates the crystalline state of metal complexes. The intermolecular hydrogen bonding interactions which connected the chains into 3D frameworks in both complexes were supported by Hirshfeld surface analysis and fingerprint plots. Also, natural bond orbital analysis divulges that the metal–ligand interaction in C1 and C2 is the LMCT. By using parameters derived from the quantum theory of atoms in molecules, the nature of Hg-ligand interaction is found to be mainly electrostatic with a small amount of covalent character. Hg(II) complexes and the corresponding ligands were also screened for their antibacterial activity against the selected Gram-positive and Gram-negative bacteria. Results indicated that C2 possess strong cytotoxic activity against the tested bacteria with MIC values ranging from 2.79 to 22.32 µg/ml. The activity of compounds was interpreted by their calculated descriptors, density, log P, and the lower unoccupied molecular orbital.