Synthesis and structural study of K 2 PbSi 3 O 9 ·H 2 O with the structure of kostylevite

Abstract

A new cyclohexasilicate, K 2 PbSi 3 O 9 ·H 2 O, was synthesized under mild hydrothermal conditions. The crystal structure was solved by powder X-ray diffraction data. The unit cell is monoclinic, a = 6.5623(2), b = 11.7757(3), c = 13.0483(3) Å, β = 103.57(2)°, space group P2 1 /n, Z = 4. The structure consists of a framework of isolated Si 6 O 18 rings with the Pb(IV) located in octahedral holes. Thus, the structural formula can be written as Pb 2 K 4 {uB, 6t}[Si 6 O 18 ]·2H 2 O. The structure encloses one eight membered monodimensional channel running parallel to the a axis of about 3.0 × 5.5 Å 2. This channel is filled with one of the two crystallographically independent potassium cations and the water molecules. A second smaller six-membered ring channel along a is also present and contains the second K +. This compound represents a monoclinic version of the better-known orthorhombic members of the family. © 2001 Elsevier Science Ltd.