Hydrothermal Synthesis, Crystal Structure, Solid-State NMR Spectroscopy, and Ionic Conductivity of Na5InSi4O12, a Silicate Containing a Single 12-Membered Ring

Na 5 InSi 4 O 12 has been synthesized by a high-temperature, high-pressure hydrothermal method and characterized by single-crystal X-ray diffraction and solid-state NMR spectroscopy. It is isotypic to Na 5 ScSi 4 O 12 . The structure consists of 12-membered single rings of corner-sharing SiO 4 tetrahedra linked together via corner sharing by single InO 6 octahedra to form a 3-D framework that delimits two types of channels along the c -axis. There are six independent sodium sites. The Na atoms within the 12-ring channels are immobile and the Na atoms within 7-ring channels are highly mobile. The 29 Si MAS NMR exhibits one Q 3 and one Q 4 resonance, each of which is split into two peaks because of inequivalent chemical environments caused by partially occupied Na sites in the 7-ring channels. Na ion conductivity measurements on a pressed pellet of the title compound were performed. The Arrhenius plot of dc conductivity shows a change in slope near 220 °C. We attribute this to the activation of the Na site that is situated between 7-ring channels and may serve as a connecting link between the channels. Crystal data: trigonal, space group R- 3 c (No. 167), a = 21.7158(9) Å, c = 12.4479(7) Å, and Z = 18.