Studies in nickel(IV) chemistry. Kinetics of the Cu(II) ion-mediated acid decomposition of tris(dimethylglyoximato) nickelate(IV) in aqueous acidic medium

✍ Scribed by G. Neogi; S. Acharya; R. K. Panda; D. Ramaswamy

• Publisher: John Wiley and Sons
• Year: 1983
• Tongue: English
• Weight: 688 KB
• Volume: 15
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550150603

✦ Synopsis

Kinetics of the Cu(I1) ion-mediated acid decomposition of tris(dimethylg1yoximato)nickelate(IV), Ni(dmg);-(dmg2-= dimethylglyoximate dianion), are reported in aqueous medium in the range of 3.6 < pH < 6.6 a t 35OC and p = 0.57M. The pseudo-first-order rate constants of the disappearance of Ni(1V) (hobs(Mj) satisfy the equation hobs(Mvl) = had -f hdec(Mi where had refers to the pseudo-first-order rate constants for the proton-assisted decomposition of the Ni(IV) complex determined independently and is a function of [H+], and h&c(Mvl) to that for the Cu(I1) ion-mediated route and is a function of [H+] and [Cu2+]. Both h & ( M ) and h d e c , ~) are found to increase with increasing (Cu(II)]o, tending to attain limiting values at higher relative [Cu(II)]". At low [Cu(II)]o the h d e c ( M) is found to register a decrease with increasing pH in the pH range of 3.6-4.4, then an increase in the range of 4.4-5.76, and again a decrease in the range of 5.76-6.6. Results on the Cu(I1) ion-mediated acid decomposition are interpreted in terms of a probable mechanism involving pH-dependent adduct formation equilibria involving the one-protonated and the two-protonated species of Ni(IV) and the various species of Cu(1I) ion in the media, followed by rate-determining acid decomposition of the adduct(s) to give Ni(I1) aq. and Cu(drngH)z. While the two-protonated Ni(1V) complex apparently reacts about five orders of magnitude faster than the one-protonated species, the aquacopper(I1) reacts about two orders of magnitude slower than the hydroxoaquacopper(I1).