Mjj. Vanvuuren et al., KINETICS OF THE FORMATION OF CARBONATOOXOVANADATE(IV) COMPLEXES AND CRYSTAL-STRUCTURE OF THE CLUSTER NA-14[V18O42(CO3)].28H(2)O, Polyhedron, 15(9), 1996, pp. 1481-1493
The aqueous kinetic and equilibrium behaviour of vanadium(IV) with bic
arbonate ions as the entering nucleophile in weak basic medium is repo
rted and the crystal structure of the sodium salt of the polyvanadate(
IV) ion containing a captured carbonate moiety, [V18O42(CO3)](14-), wa
s determined. The kinetics of the following reactions between HCO3- an
d the respective dimeric species, [V2O3(OH)(3)(H2O)(5)](-) ([Dim(H2O)(
2)](-)), and tetrameric species, [V4O8(OH)(2)(H2O)(10)](2-) ([Tet(H2O)
(2)](2-)) were studied at pH 7-9: [Dim(H2O)(2)](-)+HCO(3)(-)reversible
arrow(Kd)[Dim(H2O)-OCO2H](2-)(k-1d)reversible arrow(k1d)[Dim(CO3)](3-
) [Tet(H2O)(2)](2-)+HCO(3)(-)reversible arrow[Tet(H2O)-OCO2H](3-)(k-3t
)reversible arrow(k3t)[Tet(CO3)](4-). The rate and equilibrium data fo
r these reactions at 25 degrees C and mu = 1.0 M (NaClO4) are: K-d 2.4
(1) M(-1), k(ld) 3.8 x 10(-2) s(-1), k(3t)K(t) 4.3(3) x 10(-3) M(-1) s
(-1), Delta H-# (k(ld)) 54(4) kJ mol(-1), Delta S-# (k(ld)) - 90(4) J
K-1 mol(-1), Delta H-# (k(3t)K(t)) 29(1) kJ mol(-1), Delta S# (k(3t)K(
t)) - 192(5) J K-1 mol(-1).