RIETVELD REFINEMENT OF THE CRYSTAL-STRUCTURE OF THE SYNTHETIC POROUS ZINCOSILICATE VPI-7

The crystal structure of the zincosilicate VPI-7 with the idealized chemical formula Na-32[Zn16Si56O144].40 H2O has been refined using the Rietveld technique (R(wp) = 16.2%). The analysis confirms the proposed framework topology. The true symmetry of VPI-7, however, is orthorhombic with space group Fdd2 and a = 39.88(1) A, b = 10.326(1) A, and c = 10.219(1) A rather than the tetragonal symmetry (SG/4 ($) over bar m2) of the structure model proposed by Annen et al. The zincosilicate framework has an intersecting 3-dimensional channel system of 8- and 9-membered rings. The most characteristic feature of the framework structure is the ''spiro-5'' unit of two interconnected 3MR with zinc completely ordered in each 3MR. The zincosilicate framework is one simplest end-member structure of an OD series of which the beryllosilicate Lovdarite is the other end member.