On the Mechanism of Ligand Substitution in Weak Complexes III

Abstract

For AlSO+4 and GaSO+4 the thermodynamics and kinetics of the reaction outer‐sphere complex → inner‐sphere complex have been investigated with the pressure‐jump relaxation technique. From measurements between 10 and 40 °C the rates and energies of activation have been obtained. The equilibrium constants were estimated from the amplitudes of the relaxation effects.

Ion association and hydration in 3:2 electrolyte solutions by dielectric spectroscopy: Aluminum sulfate

“…Such a model is also consistent with the number of equilibria established for Al 2 (SO 4 ) 3 (aq) by pressure-jump and ultrasonic absorption experiments (Kalidas et al, 1971;Bonsen et al, 1978). With one exception, the resulting reduced error function v 2 r , which is normalized with respect to the number of adjustable parameters (Schrö dle et al, 2004), was significantly lower for the n = 5 fits than for those with n = 4.…”

“…Ion association in aluminum sulfate solutions has been studied by potentiometry using various electrodes (Sharma and Prasad, 1970;Matsushima et al, 1988;Ridley et al, 1999;Xiao et al, 2002), conductivity (Nishide and Tsuchiya, 1965), solubility (Ridley et al, 1999), calorimetry (Lo et al, 1982), ultrasonic absorption (Bonsen et al, 1978;Kaatze et al, 1999), stopped-flow (Knoche and Ló pez-Quintela, 1983), and pressure/temperature jump (Miceli and Stuehr, 1968;Kalidas et al, 1971) methods. Spectroscopic techniques such as NMR (Akitt et al, 1969(Akitt et al, , 1972(Akitt et al, , 1985Jin and Ichikawa, 1988;Akitt and Howarth, 1989), Raman Schö nherr, 1989, 1991a,b;Rudolph and Mason, 2001) and UV-vis (Kryzhanovskii et al, 1971;McIntyre et al, 1982) have also been employed.…”

Ultrasonic Relaxation Studies in Aqueous Solutions of Aluminium Sulphate and Scandium Sulphate

“…Thus the relaxation effects in solutions of aluminium sulphate cannot be due to a protonation reaction involving the sulphate ion. Furthermore, since the rate of formation of the inner-sphere complex is relatively slow for aluminium sulphate [7], and outside the time range of the ultrasonic equipment, the two relaxation effects observed in this study have to be attributed to the formation of solvent-separated complexes, the faster one to the reaction step 1-2 in reaction scheme (1) and the slower one to step 2 -3. Thus a three step association mechanism is the simplest scheme that seems to describe correctly the formation of aluminium sulphate complexes.…”

“…Therefore we have used small highly charged cations for which the solvating water molecules are tightly bound (causing a decrease in the rate of water release) and for which large volumes of reaction can be expected due to electrostriction of the water structure in the high electric field region surrounding the cations. Aluminium sulphate has been used as solute, since it forms inner-sphere complexes slowly (reaction times about 0.1 s to 1 s at 25°C) [7] so that the ultrasonic measurements show only the formation of solventseparated complexes. In solutions of scandium sulphate it has been possible to study the formation of the inner-sphere complex as well using ultrasonic methods.…”

“…Since, however, the relaxation times T, and T~~ differ merely by a factor of about five, Equation (10) is only an approximation. The concentrations c+ and c-are calculated from the overall association constant [7] pi = 1 + dInyi/dlnci.K , = 2OOOM-' and the activity corrections are calculated by Davies' Equation (13) (13)(consequently y2 = y3 = y4 since z2 = z3 = z4) I is the ionic strength.It has been shown [14] that Equations (10) and (13) correctly describe the relaxation times of slow reactions (relaxation times of about s) for ionic strength up to 0.2 M. They are inadequate for the reactions studied here, firstly because of the higher ionic strength, and secondly, because the activity coefficients reflect the influence of the ionic cloud which relaxes itself. According to the calculations of Onsager and Falkenhagen [ 151 this relaxation occurs at frequencies of a few MHz for 3 :2 electrolytes.…”