Cs[Si₃O₆(OH)] and Rb[Si₂O ₄(OH)]: Two novel phyllosilicates

The crystal structures of two novel phyllosilicates with compositions Cs[Si₃O₆(OH)] (caesium hydroxohexaoxotetraotrisilicate) and Rb[Si₂O₄(OH)] (rubidium hydroxohexaoxotetraodisilicate) have been characterized by X-ray diffraction. The topology of the caesium phyllosilicate silica sheet consists of interconnected four- and six-membered rings and thus differs from all of the previously reported phyllosilicates. The topology of the rubidium phyllosilicate silica sheet consists of six-membered rings only, in boat conformations, resulting in a corrugated sheet similar to that observed in δ-Na₂Si₂O₅. Both of the title compounds exhibit the characteristic sandwich structure of sheet silicates, with the Cs atom ninefold coordinated and the Rb atom eightfold coordinated to the framework O atoms.