STUDIES ON THE SUBSTITUTION-REACTIONS OF DIOXOTETRACYANOMETALATE SYSTEMS WITH BIDENTATE LIGANDS - KINETICS OF THE REACTION BETWEEN AQUAOXOTETRACYANOTUNGSTATE(IV) AND 2-PYRIDINECARBOXYLATE IONS

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.