SYSTEMATIC ENUMERATION OF 3D-NETS BY COMBINING 3-CONNECTED 2D-NETS WITH 1D CHAINS. Shaoxu Han, Department of the Geophysical Sciences, the University of Chicago, Chicago, IL 60637

Systematic enumeration of 4-connected 3D nets is an important tool for solving the unknown structures of microporous materials. Many natural and synthetic framework structures have been solved by invention of new nets. Predicted structures provide a target for synthesis of phases with interesting properties.

This poster presents systematic enumeration of 3D nets based on the association of various types of simple chains with the current set of 3-connected 2D nets from the systematic databases of subunits at the University of Chicago. The algorithm in this work is to generate 3D nets by conversion of edges of 2D nets into some simple 1D chains, such as crankshaft, zigzag and saw chain. The following enumerations have been completed: (a) conversion of all edges of 2D-nets with even-numbered circuits into the 4-repeat crankshaft chain, 57 nets of which 8 occur in known structures; (b) conversion of some edges into the 2-repeat zigzag chain with the remaining edges staying horizontal, 131 nets of which 14 occur in known structures; (c) conversion of some edges into the 3-repeat saw chain with the remaining edges staying horizontal, 172 nets of which 5 occur in known structures; (d) conversion of some edges of the hex net into a crankshaft chain 80 nets selected out of the infinite number of possible ones, of which 10 occur in known structures. Some other 3D nets are also enumerated from selected 2D nets with 1D chains up to the 8-repeat pentasil chain. Each net was checked for uniqueness in the Catalog of Theoretical Frameworks using the highest space group, cell dimensions, and topological linkages as the criteria, and then the data for each new net was incorporated into the database. Furthermore, new types of nets and chains were discovered by examining models in directions parallel to the starting net.

For selected 3D nets with higher symmetry and smaller unit cell, atomic coordinates for a 3D net were derived from the model, and cell parameters and atomic coordinates were refined using distance-leastsquares(DLS) program. The 3D-nets database provides a resource for search of unknown phases and this information can be used for structural determination with powder diffraction data.