Theoretical Study of the Interaction of 1,2-Dithiolene Ligands with the Mg2+ and Ca2+ Aquacations: Electronic, Geometric and Energetic Analysis

The B3LYP/6-311++G(d, p) method is employed to carry out calculations of the interaction strength of bidentate dithiolene ligands with the [M(H2O)(6)](2+) and [M(H2O)(4)](2+) (M = Mg or Ca) aquacations. Two series of ligands are studied: one with a phenyl ring directly bonded to the S interacting atoms and the other with a substituted ethylene (>C=C<) bonded to the two sulfide groups. These ligands present substituents with distinct induction and resonance electronic donor/acceptor effects. Fundamental characteristics, such as geometry, charges and energy of the complexed aquacations and isolated ligands, are analyzed and rationalized to correlate with the substituents effects and the metal-ligand affinity. The thermodynamic results, energy decomposition analysis (EDA) and natural bond order (NBO) show the chelate effect has an important contribution to complex stabilization and leading to an enhanced knowledge of the metal-dithiolene interaction and coordination affinity between the alkaline earth metals and sulfured ligands.