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KINETICS AND MECHANISM OF THE METAL ION CATALYSED AQUATION OF cis-DIAQUOBIS(MALONATO) CHROMATE(III) ION IN AQUEOUS-ACID MEDIA

Abstract The Cu(II), Ni(II), Co(II) and Zn(II) catalysed dissociation of the cis-diaquobis(malonato)chromate(III) ion has been studied kinetically in perchloric acid solution over a temperature range. Under these conditions k obs = kH[H+] + k cat[M2+] where k obs is the observed first order rate constants and k H and k cat are the appropriate rate constants for the proton and metal ion catalysed pathways respectively. The metal ion exert marked catalytic effects with k cat following the sequence Cu(II) > Ni(II) > Co(II) > Zn(II). A possible mechanism for the metal promoted reaction is proposed and the relevance of these results to the mechanism of the trans → cis isomerisation of [Cr(mal)2(H2O)2]− considered.