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CTURE OF INORGANIC COMPOUNDS

A Novel Representative {[Rb1.94(H2O,OH)3.84](H2O)0.1}{Al4(OH)4[PO4]3} in the Pharmacosiderite Structure Type O. V. Yakubovicha, W. Massab, and O. V. Dimitrovaa a

Lomonosov Moscow State University, Leninskie gory, Moscow, 119992 Russia e-mail: [email protected] b Philipps-Universität Marburg, Biegenstrasse 10, Marburg, D-35032 Germany Received May 7, 2007

Abstract—The crystal structure of a new synthetic aluminophosphate {[Rb1.94(H2O,OH)3.84](H2O)0.1}{Al4(OH)4[PO4]3} synthesized under mild hydrothermal conditions (T = 280°C, P = 100 atm) in the Rb2O–Al2O3–P2O5–H2O system is determined using X-ray diffraction (Stoe IPDS diffractometer, λMoKα, graphite monochromator, 2θmax = 64.33°, R = 0.032 for 312 reflections). The main crystal data are as follows: a = 7.4931(6) Å, space group P43m , Z = 1, and ρcalcd = 2.76 g/cm3. It is shown that the synthesized compound belongs to the pharmacosiderite structure type with a characteristic mixed open microporous framework composed of octahedra and tetrahedra. A comparative crystal chemical analysis of related phases is performed, and the chemical compositions of promising absorbents, i.e., hypothetical compounds potentially possible in the structure type under consideration, are proposed. It is established that pharmacosiderite and rhodizite are homeotypic to each other. PACS numbers: 61.10.Nz DOI: 10.1134/S1063774508030085

INTRODUCTION The close attention focused by modern society on ecological problems has stimulated the search for new materials that can be used as selective absorbers of the 137Cs and 90Sr isotopes from solutions of radioactive wastes and as containers for disposal of radioactive metals. In the framework of this problem, in the last decade, research works on the synthesis of microporous inorganic compounds with ion-exchange properties have been performed extensively. Unlike the wellknown organic ion-exchange materials, inorganic crystals are characterized by a higher radiation resistance, on the one hand, and possess substantially better selective properties, on the other hand [1]. Apart from conventional zeolites, in recent years, much attention has been concentrated on investigations of microporous phases with crystal structures that consist of mixed anionic frameworks formed by dissimilar polyhedra, such as typical acid tetrahedra and octahedral oxo complexes with amphoteric properties. Crystals with the pharmacosiderite structure type are characteristic representatives of this group of compounds [2–9].

orthoarsenate tetrahedra. All oxygen vertices of these tetrahedra are shared with the clusters consisting of four octahedra (Fig. 1). The three-dimensional mixed

The crystal structure of pharmacosiderite K{Fe4(OH)4[AsO4]3 ≈ 6H2O was first described by Zemann [10], who interpreted it as a framework composed of blocks of two types: clusters formed by four iron octahedra Fe4(OH)4O12 shared by edges and 409

b a

O(3) O(4)

Rb

P Al

O(2) O(1) H(1)

Fig. 1. Crystal structure of the {[Rb1.94(H2O,OH)3.84] · (H2O)0.1}{Al4(OH)4[PO4]3