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 (Na(6)Ca(1.5)FeSi(6)O(18)), 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 (Na(6.23)Ca(1.62)In(0.68)Si(6)O(18)) 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 InO(6) octahedra interconnected by 6-membered rings of [Si(6)O(18)] tetrahedra. The three-dimensional (3D) tunnel system is occupied by Na(+) and Ca(2+) charge-balancing ions. The low framework density (16.2 FC/1000 Å(3)) and high thermal stability (up to 900 °C) are comparable to other molecular sieves.