Studies on the rate of isotopic oxygen exchange between [Re(py)4O2]+ and solvent water

✍ Scribed by Fred F. Kashani; R. Kent Murmann

• Publisher: John Wiley and Sons
• Year: 1985
• Tongue: English
• Weight: 479 KB
• Volume: 17
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.550170907

✦ Synopsis

The rate of oxygen exchange between truns-[Re(py),02]+ and solvent water in py-pyH' buffer solution follows simple first-order kinetics and both oxygens are equivalent. The half-life for isotopic oxygen exchange is about 12 h at a pH of 5.0, 25"C, and [pyl = 0.10 M. The observed rate constant for exchange increases with acidity, in the pH range 4 to 6, decreases with [pyl, and is nearly independent of ionic strength. A small but significant increase of kobs occurs with increasing complex concentration. The rate of exchange follows the rate equation kobs/2 = ko + k,/[pyl with ko = 1.4 x 10-5(2) s-' and k1 = 4.7 x 10-7(1) M, s-' at 25°C. The activation parameters for the reaction a t pH = 7.15 (predominately the KO term) are: AH* = +137.(1) kJ/M and AS* = + 12641) J/MK. The pH effect and complex concentration effect are discussed in mechanistic terms. These results are compared to those found for [Re(en),Ozl' and [Re(CN),OZl3-.