Synthesis, characterization, and kinetics of formation of [Cr(H2PO4)(H2O)5]2+

Abstract

The complex [Cr(H₂PO₄)(H₂O)₅]²⁺ has been prepared from the reaction between [Co(PO₄)(NH₃)₄] and [Cr(H₂O)₆]²⁺, and characterized. Its kinetics of formation from [Cr(H₂O)₆]³⁺ and H₂PO₄^––H₃PO₄ has been studied in aqueous solution at 50, 60, and 70 °C in the range [H⁺]= 0.04–0.12 mol dm^–3, I= 1.0 mol dm^–3(LiClO₄). Only H₂PO₄^– has been found to be reactive. The rate data were consistent with an I_a mechanism. Values for the interchange rate constant (10⁴k_i) are 0.323, 1.87, and 7.71 s^–1 at 50, 60, and 70 °C, respectively (mean value for outer-sphere complexation constant, K= 1.82 dm³ mol^–1). A comparison is made with data for similar systems.