Synthesis and Stability of Wroewolfeite, [CU.Sub.4] S[O.Sub.4][(Oh).Sub.6] X 2[H.Sub.2]O *‪.‬

Abstract: Titration of aqueous copper(II) sulfate solutions with aqueous NaOH at temperatures ranging from 0 to 25[degrees]C results in a complex Ostwald step rule cascade of basic copper sulfate phases. At 25[degrees]C, the thermodynamically stable phase is brochantite [[Cu.sub.4]S[O.sub.4][(OH).sub.6], but posnjakite [[Cu.sub.4]S[O.sub.4][(OH).sub.6] x [H.sub.2]O is formed first. At lower temperatures, but above 0[degrees]C, wroewolfeite [[Cu.sub.4]S[O.sub.4][(OH).sub.6] x 2[H.sub.2]O forms first. If left in contact with the reaction solution, wroewolfeite is converted to posnjakite and brochantite in turn. However, at 0[degrees]C, synthetic wroewolfeite is stable for periods longer than a week, even in contact with the reaction solution, and a stability constant could be determined for its formation. For the reaction below, lg K = -16.3(1) at 0[degrees]C and I = 0, as determined by solution methods. 0.25[Cu.sub.4]S[O.sub.4][(OH).sub.6] x 2[H.sub.2]O(s, wroewolfeite) [??] [Cu.sup.2+](aq) + 0.25S[O.sub.4.sup.2-](aq) + 1.5O[H.sup.-](aq) + 0.5[H.sub.2]O(l)