25399-81-9Relevant articles and documents
Aqueous solution chemistry of zirconium(IV). 1. Kinetic studies on hydrogen ion and general acid (HX) induced dissociations of the tetrameric ion [Zr4(OH)8(H2O)16]8+
Devia,Sykes, A. Geoffrey
, p. 910 - 913 (2008/10/08)
The tetramer to monomer conversion [Zr4(OH)8(H2O)16]8+ → Zr(H2O)84+, i.e., Zr4 → Zr, was initiated by diluting aqueous solutions of Zr(IV) (ca. 10-2 M) in HClO4 (ca. 0.5 M) to [Zr(IV)] ≤ 10-4 M and increasing [H+] to a value in the range 2.0-4.0 M (I = 4.0 M (NaClO4)). Reactions were carried out in the presence of 2-thenoyltrifluoroacetone (HT), which complexes rapidly with Zr4+ (but not Zr4) and, since ZrT3+ is colored (λmax 366 nm), provides the means of monitoring the reaction. Data conform to the simple rate law kH[H+][Zr4], where at 25°C kH = 3.7 × 10-3 M-1 s-1. At I = 2.0 M (NaClO4), kH (25°C) = 0.95 × 10-3 s-1, and from the temperature-dependence activation parameters ΔH? = 13.2 kcal mol-1 and ΔS? = -28 cal K-1 mol-1 were obtained. Acids HX also induce the Zr4 → Zr conversion, giving the rate law KH[H+][Zr4] + kHX[HX][Zr4]. Second-order rate constants kHX (M-1 s-1) at 25°C, [H+] = 2.0 M, and I = 2.0 M are as follows: H3PO4 (80) > H2C2O4 (44) > H4P2O7 (40) > HF (30) > HSO4- (8.8) > CCl3CO2H (1.0) > CH2ClCO2H (0.4). Acetic acid (5 × 10-3 M), Cl- (2 M), and NCS- (1.2 × 10-3 M) have no effect on the conversion.
