STUDIES ON THE SUBSTITUTION-REACTIONS OF DIOXOTETRACYANOMETALATE SYSTEMS WITH BIDENTATE LIGANDS - KINETICS OF THE REACTION BETWEEN AQUAOXOTETRACYANOTUNGSTATE(IV) AND 2-PYRIDINECARBOXYLATE IONS
A. Roodt et al., STUDIES ON THE SUBSTITUTION-REACTIONS OF DIOXOTETRACYANOMETALATE SYSTEMS WITH BIDENTATE LIGANDS - KINETICS OF THE REACTION BETWEEN AQUAOXOTETRACYANOTUNGSTATE(IV) AND 2-PYRIDINECARBOXYLATE IONS, Polyhedron, 13(4), 1994, pp. 599-607
The aqueous substitution kinetics between the [WO(H2O)(CN)4]2- complex
and the bidentate ligand, 2-pyridinecarboxylate (pic-) ions, were stu
died in the pH range 6-10. Two distinct reaction steps were observed f
or which the different kinetic constants could be determined. The firs
t step involves the rapid displacement of the aqua ligand, followed by
the slower ring-closure and substitution of a cyano ligand: [GRAPHICS
] The forward and reverse rate constants for the first step in the two
-step reaction at 25.0-degrees-C and mu = 1.0 M (KNO3). were determine
d as 0.80 (8) M-1 s-1 and 0.70 (8) s-1, and for the second step as 1.7
0(8) x 10(-3) s-1 and 1.8 (5) x 10(-4) M-1 s-1, with the equilibrium c
onstants of 1.0 (2) M-1 and 10 (2) M, respectively. The ring-closure (
second step) is approximately three orders of magnitude slower than th
e initial aqua substitution. The rate constants for the first step wer
e determined by stopped-flow spectrophotometry and that of the second
step by standard spectrophotometic methods for slow reactions. The abo
ve data correlate well with that of similar systems. Additional spectr
oscopic data for [WO(eta2-bid)(CN)3]n-(bid = different bidentate ligan
ds) complexes formed by means of the above reaction are reported.