A new layered silicogermanate PKU-23 and its transformation to a zeolite with 3D channels

PKU-23, a new layered silicogermanate with eight-ring pores in the crystalline sheets, was hydrothermally synthesized under fluoride conditions by using 4-dimethylaminopyridine (DMAP) or 1-benzyl-4-dimethylaminopyridinium hydroxide (DMAP-Bn) as organic structure directing agents (OSDAs). The structure determination from single crystal X-ray diffraction showed the PKU-23 was a layered material with the double four-ring (d4r) units connected by the interrupted zigzag chains. The layers in PKU-23 were found to stack by simple translation. The OSDA cations were occluded between the adjacent layers. The topotactic condensation of layered PKU-23 resulted in a three-dimensional (3D) zeolite PKU-23-Z, which possessed a 10 X 8 X 8 channel system. The framework topology of PKU-23-Z is the same as zeolite ECNU-16. PKU-23 is the first reported zeolite precursor that could form a 3D channel system after topotactic condensation.