Supramolecular arrays, axial coordination

Perylenediimides represent another class of photoactive dyes which are characterized by their strong fluorescence emission and facile electrochemical reduction. Recently, a supramolecular bis(phthalocyanine)-perylenediimide hetero-triad (compound 42) has been assembled through axial coordination [47]. Treatment of perylenediimide 43, which has two 4-pyridyl substituents at the imido positions, with 2.5 equiv. of ruthenium(II) phthalocyanine 44 in chloroform affords 42 in 68% yield (Scheme 3). This array shows remarkable stability in solution due to the robustness of the ruthenium-pyridyl bond. Its electronic absorption spectrum is essentially the sum of the spectra of its molecular components 43 and 44 in... 

In addition to axial coordination, hydrogen bonding is another important approach to construct various supramolecular systems. This strategy, however, has not been widely used to assemble phthalocyanines and other functional units. To our knowledge, examples are so far confined to several phthalocyanine-fullerene arrays and self-assembled phthalocyanine aggregates, which are described in this section. 

Self-organization of multiporphyrin arrays into well-defined structmes, where two or more porphyrins are covalently linked together, form another set of supramolecular structures arranged through axial coordination. A combination of porphyrins with Ceo has been realized in several ways (Fig. 17). The Ceo unit forms a covalent bridge between two porphyrins, which are then oriented in a cofacial arrangement via DABCO-binding as in... 

In fact, hardly any donor atoms other than nitrogen have been used to create multiporphyrin assemblies. Using hard Lewis acids as central metal opens the possibility to bind two axial ligands on either side of the porphyrins. With ditopic Ugands such as diols this can lead to polymerization. However, a few examples can be found in the Uterature, where the central metal of the porphyrin is axially coordinated by oxygen, sulfur or selenium to assemble porphyrins. The use of (non-porphyrinic) phosphine ligands apparently has so far not been successful in the construction of supramolecular multiporphyrin arrays. 

This chapter focuses on supramolecular porphyrin systems that are stable enough to be characterized in solution. Assemblies coordinated only in solids (e.g., crystals) will not be included. In order to maintain these supramolecular structures in solution, strong complementarity and multitopic coordinations are required, rather than a simple monotopic axial coordination. Of these conditions, this discussion will be concerned only with those necessary for the complementary coordinations, and with the presentation of various examples of these coordinations. The issue of multitopic coordination will be dealt with in another forum. Self-complementary coordination can be used to obtain dimers, rings, and one- and two-dimensional arrays. These supramolecular systems should not only influence structure formation, however, but also be closely related to their functions. It is therefore natural to discuss the... 

Trimethyltin perrhenate, Me3SnRe04, forms a supramolecular array based upon Sn-O-Re-O zigzag chains, with trigonal bipyramidal, five-coordinate tin and oxygen atoms in axial positions the Sn-0 interatomic distances are 2.293 and 2.302 A [562], The diphenyltin derivative of perrhenic acid is a ladder type tetra-nuclear supermolecule, [(Re04)SnPh20SnPh20H]2, 189, as already encountered in other hydroxo tin derivatives. The Sn-0 interatomic distances are in the range 2.008-2.238 A [563]. 

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