Novel silicate anion: Si(8)O(22)(12-). Hydrothermal synthesis and X-ray powder structure of three new niobium silicates.
A sodium niobium(V) tetrasilicate, Na(2)H(NbO)Si(4)O(11).1.25H(2)O (1), was synthesized hydrothermally at 190 degrees C from a mixture of silicic acid, NaOH, NbCl(5), and H(2)O(2) and added hydrochloric acid. The successive treatment of 1 with nitric acid yielded HNb(H(2)O)Si(4)O(11).H(2)O (2). Contact of 2 with cesium hydroxide solutions converted it to the partially exchanged Cs(+) phase Cs(0.66)H(0.33)Nb(H(2)O)Si(4)O(11) (3). The three structures were solved from X-ray powder diffraction data. All compounds crystallize in the monoclinic space group P2(1)/m with Z = 2, containing the Si(8)O(22)(12-) anion. This new silicate anion type is related to the Si(4)O(11)(6-) unit, which is present in the amphibole series. The difference between both anion types lies in the chain periodicity: two for amphiboles or four for the new niobium silicates. These niobium silicates have framework structures enclosing tunnels in which the alkali cations reside.
Salvadó
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MA
Departamento de Química Física y Analítica, Universidad de Oviedo, Spain.
Pertierra
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P
García-Granda
S
S
Khainakov
S A
SA
García
J R
JR
Bortun
A I
AI
Clearfield
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A