Rb2REGaSi4O12 (RE = Y, Eu, Gd, Tb): luminescent mixed-anion double layer silicates containing chains of edge-sharing REO7 pentagonal bipyramids.

Four new rare earth gallosilicates, Rb 2REGaSi4O12 (RE = Y, Eu, Gd, and Tb, denoted as REGS-1), have been synthesized under high-temperature, high-pressure hydrothermal conditions and characterized by single-crystal X-ray diffraction. They are the first examples of rare earth gallosilicates that contain individually occupied tetrahedral Ga(3+) and Si(4+) centers. The unique structure is formed of two 1D and one 2D substructural units: unbranched achter single chains which are seldom observed in silicates, the PaCl 5-type infinite chains formed of edge-sharing REO7 petagonal bipyramids and the unprecedented mixed-anion double layers with the composition [GaSi4O12].