Self-penetration

Figure 12. 3D framework of 30 with self-penetration assembled by timpt and NiC104-6H20. 

Figure 38. Self-penetrating, self-catenating structure of Cd(CN)2- pyrazine. Circles represent Cd. Short connections between Cd atoms represent cyano bridges within the (4,4) Cd(CN)2 sheets and longer connections represent the pyrazines linking sheet to sheet Two catenated 6-gons are highlighted.

An interesting series of structures based on the rutile net illustrates the relationship between interpenetration and self-penetration. The compounds are constructed using octahedral metal ions and the trigonal ligands tcm [tricyanomethanide, C(CN) ] and dca [dicyanamide, N(CN)2 ]. It is important to note that dca is a smaller ligand than tcm. Thus, while the compounds M(tcm)2 have two interpenetrating rutile-related networks,the... 

Fig. 4 The self-penetrating network of M(dca)(tcm), with the penetration of a rod through a ring highlighted. ...

Another self-penetrating network is the (12,3) net, of which two examples were recently reported. If interpenetrating networks can be related to catenanes and rotaxanes, then self-penetrating networks can be considered to be polymeric equivalents of molecular knots. 

Batten, S.R. Robson. R. Catenane and Rotaxane Motifs in Interpenetrating and Self-penetrating Coordination Polymers. In Molecular Catenanes, Rotaxanes and Knots, A Journey Through the World of Molecular Topology Sauvage, J.-P., Dietrich-Buchecker. C., Eds. Wiley-VCH Weinheim, 1999 77-105. 

Figure 4.38 (a) A two-fold three-dimensional interpenetrating network of Co(dca)2(pyrazine) and (b) part of a self-penetrating three-dimensional network Co(dca)(tcm). 

Yu. S. Lipatov, R. A. Veselovskii, and Yu. K. Znachkov, Characteristics of the Properties of Adhesives Based on Self-Penetrating Polymer Networks, Dokl. Akad. Nauk SSSR 238(1), 174 (1978). PU/Polyester IPN adhesives. Bonding strength. 

Another fascinating discrete supramolecular architecture that has attracted considerable attention is the molecular knot. The polymeric version of a knot is a self-penetrating network indeed, this is sometimes referred to as polyknotting. ... 

Figure 19 The uninodal self-penetrating (a) (12,3) and (b) (8,4) nets. Catenane-like motifs are highlighted in each.

There are a number of uninodal nets that are also self-penetrating, notably the (8,4) net (Figure 19a) and the (12,3) net (Figure 19b). A compound containing two interpenetrating self-penetrating (12,3) nets has even been reported. ... 

Finally, the related phenomenon of self-penetration occurs when the smallest circuits of a net are penetrated... 

S. R. Batten and R. Robson, Catenane and rotaxane motifs in interpenetrating and self-penetrating coordination polymers, in Molecular Catenanes, Rotaxanes and Knots, a Journey Through the World of Molecular Topology, eds. J.-P. Sauvage and C. Dietrich-Buchecka-, WUey-VCH Ver-lag GmbH, Weinheim, 1999, pp. 77-106. 

In this net the shortest rings are interlocked and this is thus an example of self-penetrated net. 

Figure 6,4 Two different views of the twt net, a (12,3) net derived by A.F. Wells in 1954 [lOJ and synthesised by Robson and co-workers 45 years later [I I], Note the enianglemem of two 12-rings giving a self-penetrated net.

The large voids formed by some single nets are seldom empty. Besides solvent molecules and counter ions, these voids can be filled with one or more additional nets. To be classified as interpenetrating, these nets should not be able to separate without breaking any bonds. Self-penetration on the other hand is a topological property of a single net (see for example section 6.2.1) and not dealt with in this chapter. 

A reasonably simple way to derive a self-penetrating network is to cross-link 2D (4,4) sheets with bridges that lie significantly inclined to the normals of the sheets. The catenated shortest circuits then inevitably include two of the intersheet links in each circuit. For example, in the structiu e of [Cd(CN)2(pyrazine)], corrugation of the (4,4) sheets of Cd(CN)2 leads to the bridging pyrazine ligands connecting the sheets at... 

Figure 19 Self-penetrating nets based on cross-linked (4,4) sheets (a) the 6-connected net of [Cd(CN)2(pyrazine)] (b) the 8-connected net of [Znj(OH)2(bdc)4(phen)2], H2bdc=l,4-benzenedicarboxylic acid, phen= 1,10-phenanthroline. Catenated rings are highlighted in red and green in each net...

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