Rates of Inversion, Oxygen, and Cyanide Exchange

Comparison of the Rates of Inversion and Oxygen and Cyanide Exchange 

The different exchange processes described in Sections III-V can be combined to illustrate the reactivity of the different sites in these oxo cyano complexes as a function of pH and the possible interdependence thereof. The three processes that are compared are the inversion along the O-M-O axis (illustrated in Fig. 15 related to proton exchange), the oxygen exchange, and the cyanide exchange. 

Inversion of the Metal Coordination Polyhedron along the O-M-O Axis 

It was shown in Section III,D that the proton exchange processes, which can take place via two different pathways, induce oscillation of the metal center along the O-M-O axis. The inversion rate constants, inv, were calculated over a selected pH range using Eq. (18) [W(IV) and Mo(IV)] and Eq. (19) [Re(V) and Tc(V)], the appropriate proton exchange rate constants (Table IV), and the acid dissociation constants (Table II). The resulting values are presented by curves BB in Figs. 19 and 20 respectively (6). 

The different processes in the four metal centers cover a 16-order-of-magnitude reactivity range and are shown in Figs. 19 and 20. Although these are beyond practical pH ranges they illustrate a wider interpretation of all the data and are just of theoretical interest, specifically at the extreme pH values. 

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