volume and compressibility effects in the formation of meedta complexes
Kankia B.I, Funck Th., Uedaira H., Buckin V.A.
J. Solution Chemistry, 29, pp. 879-890 (1997)
We used precise measurements of ultrasonic velocity and density to study the complexation of ethylendiaminetetraacetic acid (EDTA) with Mg2+, Ca2+, Sr2+, and Ba2+ at 25°C and pH12. From these measurements we obtained the changes in the molar concentration increment of the ultrasonic velocity ΔA, the apparent molar adiabatic compressibility ΔKSΦ, and the apparent molar volume ΔVΦ of complex formation. The hydration contributions Δ(ΔVh) to the volume effect of binding range from 39.6 to 46.6 cm3/mol while the hydration contribution to the adiabatic compressibility change in the binding, Δ(ΔKh), ranges from 103.9 x 10-4 to 131.1 x 10-4 cm3/(mol bar). These data are interpreted in terms of dehydration of interacting molecules, i.e., transfer of water molecules from the hydration shells of cations and EDTA into the bulk water. The ratio Δ(ΔVh)/Δ(ΔKh) is in the range 0.35 to 0.38 bar, indicating a dominant contribution from the dehydration of charged atomic groups in the volume and the compressibility effects of complex formation.