Interpenetration topological

As for ID nets, there are a number of different ways for 2D networks to interpenetrate. The compound Ag(tcm) (tern = tricyanomethanide),C(CN)J is a coordination polymer composed of 2D chicken-wirelike (6,3) networks. The networks are corrugated and interpenetrate such that discrete layers of doubly interpenetrating networks are formed (Fig. 2a). The mean planes of the interpenetrating sheets in each layer are parallel and coincident, and the topology of interpenetration can be described as 2D 2D parallel interpenetration. The topology of interpenetration can and should be described further (see Ref. [1] for further descriptions of different possible interpenetration topologies). 

Another long-known example of 2D inclined interpenetration is the structure of trimesic acid (1,3,5-benzene-tricarboxylic acid). It contains hydrogen-bonded (6.3) sheets that interpenetrate such that each window of each sheet is penetrated by three other inclined sheets. It is also possible for more than two stacks of parallel sheets to show inclined interpenetration—the remarkable structure of Co2(azpy)3(N03)4-Me2CO-3H20 [a /73 =4,4 -azo/ zT-(pyridine)] contains four separate stacks of parallel (6,3) sheets that all interpenetrate at mutually inclined angles.Combinations of network and interpenetration topologies are also possible. Inclined interpenetration between (4,4) and (6.3) sheets has been reported,and... 

In nearly all examples of interpenetrating diamond nets, the interpenetration topology is the same, despite the varying numbers of nets. Occasionally, however, nnnsnal cases of abnormal interpenetration occnr even for this simple, highly symmetric topology. One snch case occnrs in the structure of j6-Cu(dca)(bpee). It is best illustrated by considering one net (all nets are equivalent), and the way the other nets (there are five interpenetrating nets in total) interact with it. 

This is just one illustration of abnormal interpenetration of diamond networks a small number of other examples, with different interpenetration topologies to j8-Cu(dca)(bpee), have also been reported. Interpenetration of other 4-connected topologies has also been... 

Figure 1 Four different interpenetration topologies for pairs of (4,4) sheets...

Other interpenetration topologies are also possible for diamond notably one such unusual interpenetration... 

Figure 11 Interpenetration in diamond networks (a) the two interpenetrating nets in [M(CN)2], M = Zn, Cd (b) the normal mode of interpenetration of two adamantane cavities (c) interpenetration of ten diamond nets (d) unusual interpenetration topology of adamantane cavities in the structure of 3-[Cu(dca)(bpe)] ...

Figure 12 Interpenetration of a-Po networks (a) the usual mode of interpenetration, where each cubic cavity is catenated with eight others (b) an unusual interpenetration topology where cubic cavities are catenated with 10 cavities of the other net ...

A true understanding of network structures requires analysis of not only network topology but also interpenetration topology. It is clear from the small... 

Frisch, K. C. et al., "Topologically Interpenetrating Polymer Networks", Recent Advances in Polymer Blends, Grafts and Blocks, ed. by L. H. Sperling, Plenum Press, N.Y. 19T8-... 

Some general points about interpenetrating networks can be illustrated by the example of Zn(CN)2, which was structurally characterized over half a century ago [3]. It consists of two independent diamond-like nets with the 66-a topology, in which zinc provides the tetrahedral nodes and cyanide provides linear connections between nodes. These two equivalent but independent nets interpenetrate as shown in Figure 4, such that the nodes of one net are located at the centers of the... 

Figure 9. (a) Interpenetrating undulating (6,3) nets in the structure of [Ag(tem)]. Circles in order of decreasing size represent Ag, N and C. (b) Topological essence of the interpenetration. 

Alternative modes of interpenetration for (6,3) and (4,4) nets, topologically different from those seen in Figure 9 and 10 above, can be envisaged, and real examples of some of these are known. Thus, for example, an interesting variant on the mode of (6,3) net interpenetration seen in Ag(tcm) is apparent in the structure of the semiconductor -(BEDT-TTF)2[Cu2(CN) N(CN)2) 2] (where BEDT-TTF is... 

A mode of parallel interpenetration of two (4,4) nets topologically different from that in Figure 10 is seen in [Cu(tcm)(bipy)], where bipy is 4,4 -bipyridine [11]. In this case the tern- ligands act as bent 2-connectors, as shown in Figure 12. 

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