KINETICS OF THE SUBSTITUTION-REACTION BETWEEN AQUAOXOTETRACYANOMOLYBDATE(IV) AND CYANIDE HYDROGEN-CYANIDE

The kinetics of the substitution reaction between aquaoxotetracyanomol ybdate (IV) ions and CN- and HCN, as an important intermediate step in the formation of the [Mo(CN)8]4- complex, was studied by stopped-flow spectrometry. The aqua ligand in the [MoO(H2O)(CN)4]2- Complex is sub stituted by both CN- ions and hydrogen cyanide according to the reacti on: [GRAPHICS] At 15.0-degrees-C and mu = 1.0 M (KNO3) the equilibrium , forward and reverse rate constants of the reaction with CN- ions wer e determined as 92(5) M-1, 83(1) M-1 s-1 and 0.87(3) s-1, and for HCN as 3(1) M-1, 458(5) M-1 s-1 and 140(30) s-1, respectively. Coordinatio n of the HCN to the metal centre results in a decrease in the pK(a) va lue of hydrogen cyanide by approximately 1.5 pH units to ca 7.6(2).