Kinetics and Mechanism of Oxygen Exchange and Inversion along the M:O Axis in the Diprotonated and Monoprotonated Dioxotetracyanometalate Complexes of Re(V), Tc(V), W(IV), and Mo(IV)

Abstract

Oxygen-17 NMR was utilized in aqueous medium (1.2-2.4 m KNO3) to study the oxygen exchange kinetics in the irans-dioxotetracyanometalate complexes of Re(V), Tc(V), W(IV), and Mo(IV). The kinetics are described by the two-term rate law R = (fcaq[MOH2] + &oh[MOH])/2, where MOH2 and MOH represent the diand monoprotonated forms, [MO(OH2)(CN)4]"~a nd [MO(OH)(CN)4](n+, |~, of the dioxotetracyanometalate complexes, respectively. The aqua complexes are by far more reactive toward exchange (kaq values of (9.1 ± 0.1) x 10"2 and (137 ± 5) s~' at 25.0 °C for Re(V) and W(IV), respectively), compared to the [MO(OH)(CN)4]("+1)~i ons under the same conditions (£0h: Re(V), (2.6 ± 0.3) x 10-3; W(IV), (6.5 ±0.1) x 10-4 s™1), with the kon value for the Tc(V) hydroxo oxo complex at 25 °C obtained as 13 ± 1 s_1. The activation parameters are as follows [AH* (kJ mol"1), AS* (J K"1 mor1)]• Re(V):

Oxygen-17 NMR spectroscopy: Basic principles and applications (part II)

“…The bridging OH groups do not exchange with the bulk solvent, on the NMR time scale of these experiments. 17 O NMR was utilized to study the oxygen exchange kinetics in the trans-dioxotetracyanometalate complexes of Re(V), Tc(V), W(IV), and Mo(IV) [152]. The exchange rate data of the aqua-complexes are in agreement with a dissociative activation, whereas the exchange rate of the hydroxo complexes indicates a possible interchange/associative mechanism.…”

“…As a result, a large number of experimental k, DH # , DS # and DV # values for many ions and different ligands have been derived [63,64,152,[596][597][598]747,795,796], which are listed in a number of tables in relevant reviews [807][808][809] where details of the experimental methods are also discussed.…”

“…The rate of inversion of the metal complex along the M@O axis, and the oxygen exchange for the four metal complexes were correlated as a function of pH. The authors were able to investigate inversion and oxygen exchange rates over more than a 10 orders of magnitude range [152]. The water exchange parameters for the lanthanide(III) aquaions Gd 3+ to Yb 3+ are shown in Fig.…”

Oxygen-17 NMR spectroscopy: Basic principles and applications (Part I)

“…It was concluded that, if the observation of 17 O NMR signals close to the water resonance is required, the presaturation experiment seems to be more successful compared with the 1-3-3-1 sequence [151]. The 1-3-3-1 pulse sequence was proven to be very effective in the suppression (by three order of magnitude) of the 17 O bulk water and the selective observation of bound water signal in oxygen exchange kinetic studies of complexes of W(IV) [152] (Fig. 22).…”

13C and 15N NMR Mechanistic Study of Cyanide Exchange on Oxotetracyanometalate Complexes of Re(V), Tc(V), W(IV), Mo(IV), and Os(VI)

“…The substitution and protonation behavior of the dioxotetracyanometalate complexes of Re(V), Tc(V), W(IV), and Mo(IV) have been extensively investigated in the past decade and have recently been reviewed − We have furthermore reported the characterization of these oxo complexes with NMR and were able to correlate chemical shifts and acid/base behavior with structural and infrared data. …”