16O/18O oxygen isotope exchange kinetics in MnO4− as probed by 55Mn NMR

• Published in: Russian journal of physical chemistry. B 2016, Vol.10 (4), p.582-586
• Main Authors: Tarasov, V. P., Kirakosyan, G. A.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Kinetics and Mechanism of Chemical Reactions. Catalysis; Physical Chemistry
• ISSN: 1990-7931; 1990-7923
• DOI: 10.1134/S1990793116040278

The effect of the 16 O ↔ 18 O substitution in the coordination sphere of permanganate anion MnO 4 − on the chemical shift of 55 Mn nuclei have been studied by 17 O and 55 Mn NMR. Time constants τ n,k of oxygen exchange in the water–permanganate anion system have been estimated. In nearly neutral solutions (pH ≈ 6.8–7.2), the oxygen exchange time is on the order of tens of hours. Bubbling gaseous HCl through this solution for a few seconds leads to the equilibrium distribution of oxygen isotopes in the manganese coordination sphere. The observed temperature dependences of isotope-induced 55 Mn NMR shifts in Mn 16 O 44- n 18 O n – ( n = 0–4) have been treated as a result of rovibrational averaging of Mn–O bond lengths. The change in the Mn—O bond length in caused by the 16 O → 18 O isotope substitution is on the order of 10 –4 Å.