TETRAHEDRAL NETS IN ZEOLITES, CLATHRATES, ETC: SUBUNITS & CONNECTIVITY Joseph V. Smith, Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637, USA.

The tetrahedral atoms lie at the vertices of 4-connected 3D nets. The nets can be decomposed into subunits, including 2D nets, polyhedra, chains & columns. The Catalogs of the Consortium for Theoretical Frameworks contain ~1100 theoretical nets, ~200 of which occur in materials, & >1000 subunits which are being assembled by algorithms into new 3D nets. The 3D nets & subunits are ordered by topochemical features, allowing systematic recovery. Assembly of subunits into 3D nets allows speculations on crystallization mechanisms which are tested against observed co-crystallization of synthetic zeolites and stacking errors of natural & synthetic materials. A historical review of relevant aspects of mathematical topology is underway, including sphere packing & connectivity algorithms. Complex polyhedral units form a family of derivatives from symmetric prototypes. Systematic enumeration of 4-connected 3D nets, based on the conversion of some edges of a stack of 3-connected 2D nets, is completed for 2-, 3- &4-repeat chains, and for selected nets & chains particularly important for zeolite synthesis chemists. Classification of mixed (n,m)-connected nets has begun with initiat emphasis on octahedral-tetrahedral nets, & nets containing triangles.