Enumeration of four-connected three-dimensional nets. III. Conversion of edges of three-connected two-dimensional nets into saw chains

A three-repeat saw (s) chain has each vertical edge separated by a tooth composed of two tilted edges zig and zag. Some horizontal (h) edges from a parallel stack of three-connected two-dimensional (2D) nets can be converted into an s chain. Each resulting four-connected vertex in the three-dimensional (3D) net may be part of either one, two or three s chains. The first type of (h,s)* 3D net is related by a sigma-type mirror plane to a (h,z)* net listed in paper II [Han & Smith (1998). Acta Cryst. A55, 342-359]. The second type does not have an (h,z)* relative. Using the same three-connected 2D nets as in paper II, 174 four-connected 3D nets were selected from the first two types, including six in known structures: `nepheline hydrate' (International Zeolite Association Structure Commission code JBW), AlPO₄-12-TAMU (ATT), offretite (OFF), Linde Type L (LTL), SUZ-4 (SZF) and ZSM-10 (ZST). The third type with three back-to-back s chains is represented by edingtonite (EDI), and systematic enumeration is in progress. The geometrical and topological properties of the 3D nets are given. Idealized unit-cell data and atomic coordinates for tetrahedral bonding were obtained for 40 selected 3D nets by distance-least-squares (DLS) refinement.