Nets, interpenetrating

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... 

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... 

Figure 6 A single LaPtSi-type net from the crystal structure of 6. Five more nets interpenetrate to fillthe void space created in a single net.

The second polymorph, polymorph B, can be considered as homeotypic with CaCuP (AlB2-type) structure. The structure consists of undulating hexagonal sheets. Five such nets interpenetrate to file the void space in a single net. see Venkataraman, D. Lee, S. Moore, J. S. Zhang, P. Hirsch, K. A. Gardner, G. B. Covey, A. C. Prentice, C. L. Submitted for publication to Chemistry of Materials. 

Figure 1.7 Interconversion of the highly porous, homochiral 3D MOF [Ni3(btc)2(py)6(l,2-pd)3]- (guest) upon guest desorption and exposure to ethanol vapour (a), involving transformation from a doubly interpenetrated, distorted (10,3)-a network phase to one in which four regular (10,3)-a nets interpenetrate (b). Reprinted with permission from C.J. Kepert, T.J. Prior and M.J. Rosseinsky, /. Am. Chem. Soc., 122, 5158. Copyright (2000) American Chemical Society...

Interpenetration has also been observed for other achiral types of (10,3) nets—the structures of Zn3(tpt)2X6, X = Cl, 1, contain two interpenetrating (10,3)-b nets, while [Cu(4,4 -bipy)i.5]N03-1.251120 contains six such nets interpenetrating. CoLi.5(N03)2-H20, L = l,4-bis(3-pyridyl)-2,3-diazabuta-l,3-diene, contains four (10,3)-d nets. Similar to (10,3)-a, the (8,3)-a net is chiral, and [Cu2(tae)(4,4 -bipy)2](N03)2, tae = dibasic tetraacetyl-ethane, contains four such nets of the same hand interpenetrating. ... 

Searching databases for nets, interpenetration and related problems also needs special treatment, and a section at the end of Chapter 4 deals with this. We also briefly conunent on the use of the Cambridge Structural Database, and in this context we should mention two very useful papers from the groups of Proserpio [31] and O Keeffe Yaghi [30]. 

As an example, the net in [Cd(3,3 -azodibcnzoaTc)2](Il2NMc2XNH.i) is shown in Figure 5.10 [26]. This structure contains six of these nets interpenetrated, and was constructed with non-linear optical properties (NLO) in mind. This requires a non-centrosyminelric space group, that is, there should be no inversion centre in the crystal. In the dia net is is impossible to have inversion centres at the nodes, and structures based on this net are therefore often acentric. 

By contrast. Figure 2(b) shows a situation where parallel 1D nets interpenetrate to give an overall 2D motif (lD->-2D parallel interpenetration). This type of interpenetration is shown, for example, by the structures of [Cu2L3(MeCN)2]X2-solv, L = 1,4-bis(4-pyridyl)butadiene and X = PFg , BF4, which contain interpenetrating ladderlike polymers. 43 cases such as this, where the... 

This structure also illustrates a wider observation, which is that weaker interactions between networks can often be important in the formation of interpenetrating systems, and in determining the way the nets interpenetrate. These include, for coordination polymers, interactions such as hydrogen bonding and % stacking. 

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