Rate coefficient for water exchange

A reaction sequence analogous to that in Eq. 4.40 can also be developed for the specific adsorption of bivalent metal cations (e.g., Cu2+, Mn2 or Pb2+) by metal oxyhydroxides.21 In this application the abstract scenario in the first row of Table 4.3 is realized with A = =Al-OH, B = M2+, C = =Al-OH - - M2+, D = = Al-OM+, and E = H where M is the metal complexed by an OH group on the surface of an aluminum oxyhydroxide. Analysis of pressure-pulse relaxation kinetics data leads to a calculation of the second-order rate coefficient kf, under the assumption that the first step in the sequence in Eq. 4.40 is rate determining. Like k(l, the rate coefficient for the dissolution of a metal-containing solid (Section 3.1 cf. Fig. 3.4), measured values of k, correlate positively in a log log plot with kw,. , the rate coefficient for water exchange on the metal... 

Ion-pairing is avoided by using anionic, rather than cationic, complexes and there is strong kinetic evidence [10] to suggest that a common five-coordinated intermediate Co(CN)s is involved in the substitution reactions of Co(CN)5 OH2 values of k 1 agreeing well with the rate coefficient for water exchange, viz. 

---