On the solvation thermodynamics of the neutral mercury(II) halides in different solvents at 25 °C

Abstract

Solubilities and heats of solution have been determined for the mercury( II) halides in benzene, acetone, acetonitrile, triethylamine, pyridine, di-n- butylsulfide, tetrahydrothiophene, di-n-butylamine, piperidine and hexylamine. The free energies of solution were calculated from the solubilities. The free energies of solvation were obtained by combining the free energies of solution and sublimation. The heats of solvation were obtained analogously. The entropies of solvation have then been calculated from the free energies and heats of solvation. The heats of solvation do not follow the same sequence as the Raman active symmetric stretching frequencies, v 1(HgX), which are a measure of the bond strength of the HgX bonds and indirectly also a measure of the strength of the Hg-solvate bonds. The heats of solvation are markedly less exothermic in solvents with a high degree of bulk order. The degree of bulk order depends on fairly strong intermolecular forces. The heat of solvation in one solvent can therefore be lower than in another one in spite of the fact that the solvate bonds are stronger. This is because energy is consumed when solvent molecules have to be taken out of the bulk structure when the solvation occurs.