Interpenetration 2D networks

Two major categories of interpenetrating 2D network can be discerned - one we shall refer to as parallel interpenetration and the other as inclined interpenetration . Inclined interpenetration inevitably leads to a 3D interlocked composite, whereas in all cases but one very recent one, parallel interpenetration yields a 2D composite. 

FIGURE 25. (a) The interwoven square grids of 16. The interpenetrated layers are shown in two different colors, (b) Crystallographic presentation of two fused squares within the 2D network of 16, which are interpenetrated by a square from a second orthogonal arranged layer. The phenyl groups, H atoms, and I atoms are omitted for clarity. 

The importance of host-guest interactions in the predictable formation of open square grid networks was further exemplified with the reaction of Ni(N03)2 or Cu(N03)2 and ligand 8 in the presence of benzene [21]. With Ni(N03)2 it formed a doubly interpenetrated network as the anthracene moiety prefers to interact with itself rather than with benzene (Figure 9). With Cu(N03)2 it failed to form a 2D network but formed two types of one-dimensional chains. 

Although the ID chains penetrate the 2D networks, the 2D nets do not penetrate the ID chains so it is not interpenetration. If, however, the ID nets possessed windows that were penetrated by the 2D nets (for example, if they had a ladder-like motif), then the term interpenetration would apply. 

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). 

The use of networks to describe and design crystal structures inevitably leads to the possibility of interpenetration of multiple networks. In such cases it is essential that the topology of interpenetration, as well as the individual network topology, is analysed and understood in detail. For ID and 2D networks, interpenetration can occur either in a parallel or inclined fashion, leading to overall entanglements of the same or higher dimensionality. Such systems can be described in terms of a mD(/nD) pD parallel/inclined interpenetration notation. Even highly symmetrical 3D nets such as diamond or a-Po can show, on rare occasions, different modes of interpenetration. 

Figure 9.38 (a) A 6,3-sheet of [Ag2(9.14b)3] (BF4)2 and (b) the 2D— 2D parallel Borromean interpenetrating network that it forms with the means planes of the 2D sheets coincidental. The Ag atoms (spheres) lie above each other, held by argentophilic interactions, (c) Borromean rings in black on white marble at the Cappella Rucellai in the Church of San Pancrazio, now the Marino Marini Museum, in Florence. The rings form part of the coat of arms of the Borromeo family and are also said to be a symbol of the Florentine de Medici family (photograph courtesy of Prof. L. J. Barbour).37... 

The structure of material 6 is a 2D coordination network of twofold interpenetration, in which cubane-like Cu4I4 clusters act as connecting nodes and the dps ligands as the spacer. The intramolecular Cu—Cu distances range from 2.563(1) to 2.734(2) A. Like in the case of [ Cu(p,-I)2Cu (dps)2]ra 5, ligation... 

Tadokoro and Nakasuji used the monoanionic 2,2 -biimidazoleate (HBim ) ligand in conjunction with divalent octahedral metal centres, M(II), to prepare 2D honeycomb networks based upon M(Hbim) ( building blocks linked by N-H---N hydrogen bonds in an R IO) synthon (Figure 24) [64], The overall crystal structure depends on the counter-cation used, and can be a layer structure or an interpenetrated network. The interligand N-H N hydrogen bonds can... 

Organic networks are also capable of exhibiting interpenetration. Figure 6 illustrates the threefold interpenetration that occurs in the cocrystal formed between trimesic acid (benzene-1,3,5-tricarboxylic acid) and bipy. This structure exhibits interpenetration in 2D to form a novel carpet-like architecture.54 The non-interpene-trated form of this compound has not yet been isolated. 

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