2D nets

Porosity may be generated, for instance, either by using awkwardly shaped molecules like 425 or by creating a net with large cages or channels (avoiding interpenetration)due to hydrogen bonds or coordination. In this way three-(3D) or two-dimensional (2D) nets are created which can host smaller molecules. Few... 

Parallel Interpenetration of 2D Nets to Give a 3D Interlocked Composite... 

If, as in Figure 11.14, we make the sixfold axes of all 2D nets coincide, we obtain a primitive lattice that retains all the symmetry present in the 2D lattice p6. We call this the primitive, hexagonal lattice. However, we can also choose the stacking pattern shown in Figure 11.15a, where we place the origin of the cell in the nth layer over the point 1, i in the (n - l)th layer. The result of this stacking scheme is seen in elevation in Figure 11.156. It has several important properties. 

Hexagonal symmetry is lost Since the sixfold axes of the 2D net have been made coincident with threefold axes, only the threefold symmetry survives. The reason that this is nevertheless still called a hexagonal lattice will be given in Section 11.5. 

In this very brief survey we have not been concerned with the detailed structure of the layers, various aspects of which are discussed in more detail later, in particular the basic 2D nets and structures based on the simplest 3- and 4-connected plane nets (Chapter 3), and layers formed from tetrahedral and octahedral coordination groups (Chapter 5). The Cdl2 layer and more complex structures derived from this layer are further discussed in Chapter 6. We shall see that there are corrugated as well as plane layers, and also composite layers consisting of two interwoven layers (red P, Ag[C(CN)3]) these are included in the chapters just mentioned. 

A fundamental contribution is represented by a famous series of articles and books on crystal chemistry published many years ago by A. F. Wells [4], who analysed and classified a great number of nets. Fie emphasized the importance of describing a crystal structure in terms of its basic topology such a description not only provides a simple and elegant way of representing the structures but also evidences relations between structures that are not always apparent from the conventional descriptions. Wells introduced a method for the systematic generation of 3D arrays from 2D nets and also described many hypothetical motifs that were successively discovered within the realm of coordination polymers or of other extended systems. Flis results included a list of many simple nets described with only one kind of node (uninodal) or with two nodes of different connectivity (mainly binodal 3,4-connected). 

Polycatenation of ID and 2D nets can occur essentially in two modes that are described as parallel and inclined , according to the nomenclature introduced by Batten and Robson [2]. 

Self-catenation is observed not only in 3D nets but also in 2D nets a few rare examples are known (see Ref. [3]) and two recent examples are the 4-con-nected layers in a Cd coordination polymer (G. O. Lloyd, J. L. Atwood, L. J. Barbour, Chem. Commun. 2005, 1845) and the 6-connected layers in a supramolec-... 

A particularly novel 2D net based on pentagons (which cannot tessellate in two dimensions) is also known. The net topology is (5, ) in Wells nomenclatnre, meaning that it is composed of 3- and... 

Tritopic tricyano derivative 20 [41] or 22 [45] and the Ag ion (AgOTf) in the trigonal-bipyramidal geometry form a (3,3)-connected 2D net composed of a hexagonal 21 or 12-annulene-like cyclic motif 23, respectively (Figs. 6 and 7). 

Fig. 9. 2D net formed by 29 (side view in 30 and top view of two adjacent sheets in 31) or 32 (side view in 34). G stands for the guest bound via hydrogen bonding... 

The molecular sheets can remarkably also be linked by covalent bonds. An alkane- or arenesulfonate anion (RSOj) 54 and the guanidinium cation 55 form an interesting inorganic 2D net 56, in which the organic moieties Rs are sticking out of the sheet (Fig. 14). The sheets are intercalatively layered in an R-depen-dent manner (57 for the top view) [62]. A simple use of an alkane- or arenedi-sulfonate 58-62 (Fig. 14) results in covalent linkage of the neighbouring sheets (63) [30]. 

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