Structural and mechanistic investigation of rubidium ion exchange in potassium zirconium trisilicate

Complete and intermediate incorporation of rubidium into the hydrothermally prepared mineral umbite has been accomplished by ion exchange. Potassium zirconium trisilicate, K2ZrSi3O9·H2O, is an open framework ion exchanger composed of polymeric chains of trisilicate groups linked by zirconium atoms. This arrangement creates a three-dimensional tunnel network. The exchangeable cations are found in two unique tunnels along the c-axis inside the framework. Site 1 is marked by a 12-membered ring and contains two cations. Site 2, a 16-membered ring, contains two cations and two water molecules. The parent compound, K2ZrSi3O9·H2O, was used to prepare compound 1, Rb2ZrSi3O9·H2O, in which the original space group, P212121, is conserved. Cell dimensions of a = 10.4821(6) A, b = 13.3869(5) A, and c = 7.2974(3) A were found for compound 1. Analysis of Rb−O coordination shows average contact distance approaching the sum of the O2- and Rb+ ionic radii. Compound 2, K0.29H0.1Rb1.61ZrSi3O9·H2O, shows that Rb+ has complete...