Interpenetrating 10,3 -a Nets

Figure 22. Two distorted interpenetrating (10,3)-a nets in the structure of [Ag2(2,3-dimethylpyra-zine)3](SbF6)2. Circles represent Ag.

Figure 9.5 The view along the fourfold helix in one of the eight interpenetrating (10,3)-a nets in [Zn(9.1)2/3(SiF6)(H20)2(Me0H)]-solvent. Helices are highlighted by imaginary poles running along the selected helical axes (reproduced with permission from The Royal Society of Chemistry).

In its geometrically most regular form, shown in Figure 21, the (10,3)-a net has cubic symmetry and angles at nodes are all 120°. 4-Fold helices run parallel to the axes. All the helices have the same handedness, making the net as a whole chiral. Wells foresaw, before real examples were known, that the (10,3)-a net is in principle capable of participating in interpenetration not only with an identical net... 

Figure 25. (a) Three interpenetrating (10,3)-b nets with T-shaped 3-connecting nodes in the structure of [Ag(bipy)]N03. Circles represent Ag atoms. Long connections are via bridging bipy units and short connections are direct Ag... Ag interactions, (b) An idealized version of the mode of interpenetration of three (10,3)-b nets, of the type seen in [Ag(bipy)]N03. 

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...

Robson. R. A Wellsian 3D racemate Eight interpenetrating, enantiomorphic (10.3)-a nets, four right handed and four left handed. Chem. Coinmun. 1996. 1313-1314. 

Figure 10 Interpenetration of two (10,3)-a nets that (a) are of opposite handedness and (b) are of the same handedness. The chirality of each net can be seen by examining the fourfold helices going into the page.

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. ... 

The introduction of chirality into networks leads to another way that nets can interpenetrate in different ways. For example, the (10,3)-a net is inherently chiral, meaning that the interpenetrating nets may be of all the same handedness, of opposite handedness, or a combination of both (in equal or unequal numbers). Interpenetration of two (10,3)-a nets with either the same or the opposite handedness is shown in Figure 13. As examples, [Ni3(btc)2(pyridine)g(eg)g]. 3eg. 4H20, btc = benzene-... 

As we are talking about volumes, we should add that Wells also noted that a cubic close packing (face centred close packing) can be broken down into several interpenetrating nets for example four (10,3)-a or srs nets or three (10,3)-b or ths nets [8]. 

An example of C is probably [[Co(lll)(5-(4-p)Tidyl)-4,6-dipyrrinato))3]Ag] S03CF3forming doubly interpenetrated utp or (10,3)-d nets [16]. The Co(lII) ion probably forms a kinetically inert im-ehelated eomplex in solution while the Ag(l) ion is more labile. 

We know of only two examples of parallel 2D interpenetration involving nets other than (6,3) and (4,4). One is Hittorf s phosphorus, in which two 82-10 nets, composed entirely of phosphorus atoms, interpenetrate [15], The other example, considered in the next section, differs from all the other parallel interpenetrating cases in that the composite formed is a three-dimensional interlocked structure. 

Another Py-GC/MS experiment was performed on polyacrylic /nfer-net-polysiloxane, a copolymer used as impact properties modifier. This is a polymer of butyl acrylate with low levels of allyl, methyl, and 3-(dimethoxymethylsilyl)propyl methacrylates interpenetrated with cyclic dimethylsiloxane. The copolymer has CAS 143106-82-5. The pyrolysis was done at 600 C in He similar to other experiments previously discussed. The pyrogram is shown in Figure 6.7.14 and peak identification is given in Table 6.7.10. 

The main feature of polycatenation is that the whole catenated array has a higher dimensionality then that of each of the component motifs. These motifs can, in principle, be OD, ID or 2D species that must contain closed loops and that are interlocked, as for interpenetrating nets, via topological Hopf links [31] (see Fig. 1.3.11). Each motif can be catenated with a finite or also with an infinite number of other independent motifs but not with all (see Fig. 1.3.10). 

Fig. 10 (a) Coordination environment of Co, showing the building unit of [Co3(bpdc)3(bpy)] (8). (b) Packing diagram of one of the two nets of 8 viewed down the b axis, (c) Twofold interpenetrating 3D networks viewed down the a axis, (d) Space-filled model of 8 viewed perpendicular to the (001) plane... 

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. 

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