The nature of the metal-ligand chemical bond and the electronic structure of Be, Mg, and Zn acetylacetonates and hetero- and β-substituted analogs

The effect of valence molecular orbitals on the nature of the chemical bond of the p-metal ion with chelate ligands in Be(acac)2, Mg(acac)2 and zinc Zn(acac)2 was studied by theoretical methods. The effect of the substitution of atoms and functional groups in the ligands on the chemical bond was estimated. For beryllium, the bond is almost completely covalent with an insignificant ion component: the Coulomb potentials for complexes with beryllium are 1.37 and 1.08 eV for acetylacetonate and hexafluoroacetylacetonate, respectively. For Mg and Zn β-diketonates with a metal-oxygen bond, the calculations showed the essentially ionic nature of binding: about 8 eV for magnesium compounds and 12.3 and 11.3 eV for zinc. However, the O→S substitution significantly reduces the metal-ligand binding iconicity: to 2.8 and 0.9 eV for the thio- and dithio-substitution, respectively. The covalent bond of a metal with ligands is due to the overlapping of only some MOs with s- and p-orbitals of the metal. The covalence of the M–O bond in acetylacetonates decreases in the series Be→Mg→Zn due to an increase in the ionic radius of the metal, leading to two consequences.