NA3HX(H2PO4)X[(GEO)4(GEO4)3]CENTER-DOT-4H2O - A RHOMBOHEDRALLY-DISTORTED GERMANIUM PHARMACOSIDERITE ANALOG WITH ANION-CATION EXCHANGE CAPABILITIES

A rhombohedrally distorted germanium pharmacosiderite analog, with the stoichiometry of Na3Hx(H2PO4)x[(GeO)4(GeO4)3].4H2O, x almost-equal-to 1.38, has been synthesized under mild conditions. As synthesized, this material contains both sodium cations and hydrogen phosphate anions as included species. Both monovalent/divalent cations and a variety of anions are easily exchanged in and out of the framework under aqueous conditions at room temperature. Depending on the ions incorporated, the crystal structure can be transformed to the cubic system [space group P43mBAR (No. 215)] and then back to the rhombohedral system. It appears that the incorporation of a sodium cation and any anion will induce the rhombohedral distortion. Rietveld refinement of room-temperature powder X-ray and low-temperature time-of-flight neutron powder data confirmed the space group R3m (No. 160) with a = 7.7121 (4) angstrom and alpha = 89.04 (3)degrees, final R = 3.32 % and R(w) = 3.93 % (chi2 = 5.055) for 63 variables and 10 693 observations. Crystallographic data for two ion-exchanged cubic frameworks are included along with data for a synthetic cubic K3H[(GeO)4(GeO4)3].4H2O [K/Ge] framework. Further analytical studies, such as P-31 MAS NMR and FTIR, were used to confirm the presence or absence of cation and/or anion exchange for all analogs studied.