PKU-20: A new silicogermanate constructed from sti and asv layers

A new silicogermanate (PKU-20) was hydrothermally synthesized using triethylisopropylammonium cation as the structure directing agent in the presence of fluoride. Its structure was determined from a combination of synchrotron single crystal X-ray diffraction and powder X-ray diffraction data. PKU-20 crystallizes in the monoclinic space group C2/m, with the lattice parameters of a = 18.5901(6) Å, b = 13.9118 (4) Å, c = 22.2614 (7) Å and β = 100.1514 (12)°. The framework of PKU-20 is constructed from an alternate stacking of sti and asv layers. The sti layer is exactly the same as that in the STI framework,while the asv layer is a new layer sliced off from the ASV framework parallel to the (112) plane. The take-out scheme of the layer is discussed on the basis of a composite building unit "D4R-lau-D4R". PKU-20 possesses a two-dimensional channel system, where the 10-ring channels parallel to the [010] direction are intercrossed by 12-ring pockets along the [101] direction.