Design of Molecular Building Blocks for the Development of Nickel(II)-Chelating Agents

The affinity of the pentaaqua Ni2+ cation for 16 neutral ligands with distinct functional groups was analyzed with the DFT method. The metal-ligand binding strength was calculated by the interaction enthalpy and Gibbs free energy for the exchange of a water molecule from the [Ni(H2O)(6)](2+) by a neutral ligand. Geometrical, electric and energetic features of the isolated ligands and the complexes were correlated with the intensity of binding. All the substitution enthalpies and Gibbs free energies are negative, showing exothermic and spontaneous processes. The affinity order is P=O > C=N > C=S > C=O > C-N > C-S > C-O ligands. The EDA calculation reveals that the ionic and the covalent terms are both important in determining the interaction order strength. The electrostatic term is the most relevant for modulating the metal cation interaction. The electric nature of each ligand dictates the metal-ligand bonding strength. Ligands containing the phosphate group have the strongest interaction with the Ni2+ aquacation and are indicated to be the structural anchoring blocks of chelation agents for aquatic resources decontamination.