Hydrothermal synthesis and structures of the open-framework copper silicates Na2[Cu2Si4O11](H2O)2 (CuSH-2Na), Na2[CuSi3O8] (CuSH-3Na), Cs2Na4[Cu2Si12O27(OH)2](OH)2 (CuSH-4NaCs), and Na2[Cu2Si5O13](H2O)3 (CuSH-6Na)

A series of open-framework copper silicates has been synthesized under mild hydrothermal conditions. The frameworks are based on double chains, single layers or double layers of SiO4 tetrahedra interconnected by CuO4 squares or tetrahedra or CuO5 tetragonal pyramids. The structures contain 8-ring or 10-ring channel systems with apertures up to 2.7×5.9Å which are filled by alkali metal cations and water molecules.