Thermodynamics of the Formation of Complexes and the Hydrogen Bonds between Oxyanions and Water

Abstract

The most stable structures of 32 complexes containing oxyanions with HOH···A⁻ are optimized according to density functional theory M06-2X with basis set 6-311++G(d,p). Thermodynamic characteristics of the formation of complexes are calculated with allowance for the basic superposition error (BSSE), and correlations with the enthalpy of formation of ion-molecular hydrogen bonds (ΔH^Iog) (Johansen’s formula) are found. The contribution from enthalpy ΔH^Iog to the enthalpy of formation of HOH···A⁻ complexes changes in the range of 12 to 54%. Molecular graphs of complexes are calculated according to QTAIM and the densities of the full energy of electrons at critical point (3, −1) of O–H···O bonds are analyzed. As the values of ΔH^Iog grow in the range of 28.0 to 58.4 kJ/mol, the contribution from the covalent constituent to the formation of O–H···O bonds increases as a result of stronger polarization interaction between anions and water molecules.