KINETICS AND MECHANISM OF REACTION OF EUROPIUM(II) AND OXOVANADIUM(IV) IONS IN SOLUTIONS CONTAINING PERCHLORATE AND/OR COMPLEXING ANIONS

The oxidation of Eu2+ by VO2+ occuss according to a rate expression K[Eu2+][VO2+], with k = 2.64 ± 0.09 × 103 M−1 sec−1 at 25.0˚ and unit ionic strength. The products are Eu3+and V3+; subsequent reduction of V3+ by Eu2+ occuss much more slowly. Activation parameters for the reaction are ΔH‡ = 2.83 ± 0.30 kcal mol−1 and ΔSDagger; = –33.4 ±1.0 cal mol−1 deg−1. The reaction was also studied in the presence of thiocyanate, azide, and chloride ions. AU three anions increase the rate of oxidation of Eu2+, suggesting oxidation of VO(X)+ by Eu2+. In the presence of >0.1 MSCN−, (H2O)5VNCS2+ was detected as a product; the failure to detect VCl2+ is probably due to its high aquation rate. © 1969, American Chemical Society. All rights reserved.