Porphyrins hexagonal

Mineral Surfaces. Organic matter is chemically adsorbed (deriva-tized) at the surfaces of clay minerals, zeolites, and related minerals (105) and is at times protected, concentrated, and degraded by contact with the solid surfaces. For example, porphyrins are protected (106), as are optically active amino acids by montmorillonite (107). This may result in part from the position of the organic matter in lattice spaces, as shown by Stevenson and Cheng (108) for proteinaceous substances keyed into hexagonal holes on interlamellar surfaces of expanding lattice clays, or from the fact that there are ordered structures at solid-water interfaces (109). 

It is also possible to study the self-assembly of individual molecules as well as networks such as 15.3. The V shaped zinc(II) bis (porphyrin) shown in Figure 15.20a self assembles into decaporphyrin pentagonic and dodecaporphyrin hexagonic assemblies. The assemblies can be fixed by alkene metathesis using Grubbs catalyst. This process represents self-assembly followed by covalent modification as described in Section 10.3.2. The assemblies can be directly imaged by high resolution STM (HRSTM)... 

Phthalocyanines and porphyrins are often used as model compounds for the manipulation (guest molecule) of surface-supported supramolecular two-dimensional arrays both in UHV and in solution. Spillmann et al. reported that zinc(II) 5,15-bis(3-cyanophcnyl)-10,20-bis 3,5-di(/c/7-bu(yl )phcnylj porphyrin, 2, molecules predominantly formed a hexagonal pattern by trimer formation, when 0.5-0.7 MLs of 2 was deposited on Ag(l 11) especially, 2 forms a characteristic nanostructure on Ag(l 11) at low coverage [163], As reported by Yokoyama et al., it is suggested that the molecular assembly is driven by both van der Waals and dipole-dipole interactions involving the polar 3-cyanophenyl residues [79], After further deposition of C60... 

Most of what has been aid so far applies to rod-like molecules, but similar phases exist for disk-shaped molecules, such as porphyrins and phthalo-cyanines. These tend to form phases in which the director is now orthogonal to the plane of the molecule. Thus, where the planes of the molecules are more or less parallel, but with no positional ordering into columns, the phase is a nematic discotic. If, however, the macrocycles form themselves into columns as well, we have a columnar smectic phase. A loose analogy of this phase is that it is like stacked coins, with the stacks arranged in a hexagonal lattice. 

Figure 96. Crystal structure of Zn(TPyP) CH, 0H-2H 0. The marked hexagons indicate hydrogen-bonding interactions between six water molecules and pyridyi groups of porphyrins in adjacent unit cells. Reprinted with permission from Krupitsky, H. Stein, Z. Goldberg. I.y. Inclusion. Phenom. Mol. Recognit. Chem. 1994, 18, 177.

Figure 7 Examples of dative directed assemblies (a) Wasielewski porphyrin trefoil that uses diazo-bicyclic octane to form a trimer with a hexagonal center cavity (b) Stang s tetrameric structures are formed by the assembly of two -platinum phenanthrenes and 2 disodium carboxylates " ° (c) Three fciT-platinum benzophenone units and three disodium carboxylates organize to form hexagonal structures.

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