Self-complementary building blocks

In designing ever larger diamondoid networks, it is important to retain the approximate T(i symmetry of the building blocks. This may be achieved via a single self-complementary building block such as 8.59 which possesses four mutually complementary carboxylic acid groups, or by a modular approach, which uses a combination of a TA (or at least, S 4) node such as the cubeane cluster [Mn(CO)3( j,3-OH)] 4 (8.60) and a linear spacer (A-A) (Figure 8.76). 

The first examples of porphyrin coordination polymers that have been characterized according to our definition in Sect. 3.1 were reported in 1991 by Fleischer and Shachter [72]. Upon metalation of 5-pyridyl-10,15,20-triphenyl-porphyrin with a Zn " ion, a self-complementary building block was obtained which readily assembles to polymer 19 as confirmed by concentration dependent UV/vis spectroscopy and NMR studies. The structure of the polymer 19 in the solid state was established by X-ray analysis. Recent reinvestigations of this system suggest that in solution tetrameric squares prevail, and polymer formation may take place at higher concentration (> 1 M) as predicted by computer simulation [12]. 

Complementary to using repulsive interactions in order to achieve shape control, attractive interactions of relatively large building blocks, which are rationally designed regarding their shape, polarity, and functional groups, can be employed for intramolecular self-assembly [23]. In this case, the molecular structure optimizes itself to realize specific interactions between the blocks and minimize the interfacial energy. 

Figure 8.76 Construction of diamondoid networks via self-assembly of self-complementary 54 building blocks or modular self-assembly of mutually complementary 54 nodes and linear spacers.

Figure 10.43 (a) Self-assembly of two mutually complementary curved building blocks to produce a... 

Figure 4 Schematic representations of the formation of 1-D inclusion networks based on koiland, building block possessing two divergent cavities, and connector molecules (a, d, e-h) or through self-inclusion by self complementary koilands (b, c, i-1). For definition, see text.

Noncovalent self-assembly of complementary pairs of homoditopic building blocks (AA/BB-type), such as bis(crown ether) 125 and diammonium salt 126, has afforded well-defined supramolecular oligomeric/polymeric assemblies <2003JA3522>. In dilute solutions, entropy favored the formation of the cyclic dimer, whereas high equimolar concentration (>0.5 M) of the two components led almost exclusively to linear species aggregation, as revealed by H NMR analysis and viscosity measurements. Closely related linear poly[3]pseudorotaxane supramolecular arrays have also been prepared from cylindrical bis(crown ether) 127 and bisparaquat derivative 128 <2005CC1696>. 

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