The synthesis and characterisation of JBW-type zeolites. Part A: Sodium/potassium aluminosilicate, Na2K[Al3Si3O12]center dot 0.5H(2)O

Bulk zeolite JBW, Na2K[Al3Si3O12]. 0.5H(2)O, has been synthesised under hyd rothermal conditions (225 degrees C) from a solution containing both sodium and potassium ions. The structure has been refined, at room temperature an d at 4 K, from powder neutron diffraction data. Sodium ions occupy sites in the non-hydrated cristabolite layers while the eight-ring channels contain lines of alternating potassium ions and water molecules. The positions of the water molecules have been fully determined, including their hydrogen bo nding interaction with the framework. The dual templating effect of sodium and potassium at different sites in the JBW structure seems to be a prerequ isite for the formation of pure JBW from aqueous solution. (C) 2000 Elsevie r Science B.V. All rights reserved.