KINETICS OF THE FORMATION OF CARBONATOOXOVANADATE(IV) COMPLEXES AND CRYSTAL-STRUCTURE OF THE CLUSTER NA-14[V18O42(CO3)].28H(2)O

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).