Natural bond orbital analysis of dication magnesium complexes [Mg(H₂O)₆]²⁺ and [[Mg(H₂O)₆](H₂O)_n]²⁺; n=1-4

The metal ion is ubiquitous in the human body and is essential to biochemical reactions. The study of the metal ion complexes and their charge transfer nature will be fruitful for drug design and may be beneficial for the extension of the field. In this regard, investigations into charge transport properties from ligands to metal ion complexes and their stability are crucial in the medical field. In this work, the DFT technique has been applied to analyze the delocalization of electrons from the water ligands to a core metal ion. At the B3LYP level of approximation, natural bond orbital (NBO) analysis was performed for the first five distinct complexes [Mg(H2O)6]2+ and [[Mg(H2O)6](H2O)n]2+; n = 1-4. All these complexes were optimized and examined with the higher basis set 6-311++G(d, p). In the complex [Mg(H2O)6]2+, the amount of natural charge transport from ligands towards the metal ion was 0.179e, and the greatest stabilization energy was observed to be 22.67 kcal/mol. The donation of the p orbitals in the hybrid orbitals was increased while approaching the oxygen atoms of H2O ligands in the 1st coordination sphere with the magnesium ions. The presence of water ligands within the 2nd coordination sphere increased natural charge transfer and decreased the stabilizing energy of the complexes. This may be due to the ligand-metal interactions.