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, thi s 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, t he crystal structure can be transformed to the cubic system [space gro up P43mBAR (No. 215)] and then back to the rhombohedral system. It app ears that the incorporation of a sodium cation and any anion will indu ce the rhombohedral distortion. Rietveld refinement of room-temperatur e 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 a nd 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 da ta for two ion-exchanged cubic frameworks are included along with data for a synthetic cubic K3H[(GeO)4(GeO4)3].4H2O [K/Ge] framework. Furth er analytical studies, such as P-31 MAS NMR and FTIR, were used to con firm the presence or absence of cation and/or anion exchange for all a nalogs studied.