Novel silicate anion: Si(8)O(22)(12-). Hydrothermal synthesis and X-ray powder structure of three new niobium silicates.
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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.
author list (cited authors)
Salvad, M. A., Pertierra, P., Garca-Granda, S., Khainakov, S. A., Garca, J. R., Bortun, A. I., & Clearfield, A.
complete list of authors
Salvadó, MA||Pertierra, P||García-Granda, S||Khainakov, SA||García, JR||Bortun, AI||Clearfield, A