Diamondoid architectures

Figure 9.8. Diamondoid architectures that can potentially be obtained by self-assembly of tetrahedral-based dendrimers.

A diamondoid architecture also results when Zn(CN)2- is reacted with Cu(I). The resulting anionic network might be viewed as tetrahedral zinc nodes linked to tetrahedral copper nodes by cyanide spacers, however the nature of coordination at the copper and zinc ions remains unclear. Analysis of the structural data indicated that it is most appropriate to consider the coordination of the copper as 100% organometallic (Cu-C) and the coordination of the zinc 100% metal-organic (Zn-N). The ionic nature of this particular framework means that the presence of a counterion in the resulting cavities is required. Indeed, N(CH3)4 fits comfortably inside the adamantoid cavity and precludes interpenetration. 

Figure 9.1 Schematic representation of some of the simple network architectures structurally characterised for metal-organic polymers (a) 2D honeycomb, (b) ID ladder, (c) 3D octahedral, (d) 3D hexagonal diamondoid, (e) 2D square grid, and (f) ID zigzag chain (reprinted from Section Key Reference The American Chemical Society).

N. R. Organically templated three-dimensional open-framework metal selenites with a diamondoid network. J. Mater, Chem. 2003. 13, 1635-1638. (d) Behera, J. N. Ayi, A. A.. Rao. C. N. R. The First Organically Templated Open-Framework Metal Selenate with a Three-Dimensional Architecture. Chem. Commun. 2004, 456-457. 

The use of transition metals or transition metal clusters to act as nodes for the modular self-assembly of diamondoid networks that are sustained by coordinate covalent bonds is also well established. Such architectures are of more than aesthetic appeal. Indeed, such structures have resulted in a class of compound with very interesting bulk and functional properties. Metal-organic diamondoid structures in which the spacer moiety has no center of inversion are predisposed to generate polar networks since there would not be any inherent center of inversion. Pyridine-4-carboxylic acid is such a ligand and bis(isonicotinato)zinc exists as a three-fold diamondoid structure that is thermally stable and inherently polar.33... 

Diamondoid networks represent just one example of the types of architecture that can be generated in a rational manner using the modular self-assembly approach. The remainder of this chapter will focus upon the diversity of simple architectures that are accessible using crystal engineering strategies, many of which have no precedent in minerals yet are afforded via one-pot reactions and commercially available components. 

Halogen halogen interactions have also been used to design even more complex architectures, and the crystal structure determination of 1,3,5,7-tetraio-doadamantane reveals the presence of a 3-D diamondoid-like network established through multiple iodo- dodo interactions [57, 58]. 

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