Self-catenated Networks

Probably the first examples of 3D self-catenated frameworks within coordination polymers were described by Robson and coworkers [49], In the species [Cd(CN)2L] [L = pyrazine or l,4-bis(4-pyridyl)butadiene] the Cd(CN)2 sublattices form 44 undulated layers that are joined in a criss-cross fashion by the L spacers. Catenated hexagonal chair-like circuits are observed in the interlayer connections (see Fig. 

9) that was enumerated by Wells [4b] but never found previously in real species. 

Within uninodal 3-connected nets this is special in that it contains relatively large shortest rings (12-gons), the largest n-gons considered by Wells. 

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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... 

What about the other components of the network Is carbon unique in its group It most certainly is. No other element is so special that it has an entire branch of chemistry built around it Carbon is arguably the most striking example of an element being unlike its heavier congeners, as one can find in the periodic table. This will be particularly evident when we explore the ability of carbon to catenate (form self-links with itself) and to form tt bonds. 

Ni(tpt)(NOp2-solv (b) a self-penetrating (8,4) network. Catenated rings are highlighted in green and pink in each net... 

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