Indium silicate with an imandrite-type structure

This work reports the synthesis and characterization of novel zeolite-like indium silicate MS-2 (Minho-Sofia, solid number 2). The structure of this material is analogous to that of the mineral imandrite (Na6Ca1.5FeSi6O18), with In instead of Fe in the octahedral position. MS-2 is the first structurally confirmed indium silicate prepared under mild hydrothermal conditions and the only synthetic indium silicate related to the lovozerite mineral group. MS-2 (Na6.23Ca1.62In0.68Si6O18) exhibits significant indium deficiency in the octahedral position thus having the highest Si/In (8.8) ratio among the known indium silicates. The framework consists of occupationally disordered InO6 octahedra interconnected by 6-membered rings of [Si6O18] tetrahedra. The three-dimensional (3D) tunnel system is occupied by Na+ and Ca2+ charge-balancing ions. The low framework density (16.2 FC/1000 angstrom(3)) and high thermal stability (up to 900 degrees C) are comparable to other molecular sieves.