An attempt to parameterize the structuredness of solvents

An attempt has been made to parameterize the structuredness of solvents from the viewpoint of intermolecular interactions, and the structuredness parameter S _p has newly been proposed. The enthalpy of vaporization H _vap ^/o of various solvents has been considered to consist of donor-acceptor interaction energy (DA), which can been estimated from Gutmann's donor and acceptor numbers, some other interaction energies (VDW), which may not be fully described in terms of the donor-acceptor interactions and may be related to the electronic distribution, the volume and shape of the molecule, the polarizability and ionization potential of atoms in the molecule, the energies of these interactions being usually considered to be of Van der Waals type and possibly evaluated from the enthalpy of vaporization ofn-alkanes, and the intermolecular interaction energy (STR) due to the three-dimensional molecular ordering in the liquid: H _vap ^/o =DA+VDW+STR. The STR term obtained as the difference between H _vap ^/o and (DA+VDW) is defined as the structuredness parameter S _p , which is a dimensionless quantity by dividing the value with the (kJ-mol^–1) unit. The entropies of formation S ₁ ^o and S ₄ ^o of MX]⁺ and MX₄]^2– complexes, respectively, of divalent metal ions (Mn²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, and Hg²⁺) with halide and thiocyanate ions in aqueous and nonaqueous solvents could be represented as an almost linear function of the structuredness parameters S _p .