MOLECULAR TECTONICS WITH FUNCTIONALIZED PORPHYRINS

R. Krishna Kumar and Israel Goldberg

School of Chemistry, Sackler Faculty of Exact Sciences, Tel-Aviv University, 69978 Ramat-Aviv, Tel-Aviv, Israel, E-mail: goldberg@post.tau.ac.il

Keywords: coordination polymers, crystal engineering, hydrogen-bonded networks, porphyrin aggregates, supramolecular chemistry, nanoporous solids, molecular recognition

The ability to control the supramolecular organization of molecular entities by noncovalent interactions is a challenging goal in materials science, on the road to formulating new compounds with potentially useful properties for relevant scientific and technological applications. In this context, the design of multiporphyrin architectures has drawn a considerable attention in recent literature, as such materials have diverse potential as biomimetic models of photosynthetic systems and as functional molecular devices (the latter including nanoporous molecular-based solids of structural and functional similarity to the inorganic zeolites). Tetraarylporphyrins provide attractive building blocks for such crystal engineering, as they can be easily 'programmed' by addition of various substituents and recognition sites to the porphyrin periphery, as well as by varying the nature of the metal atom inserted into the porphyrin core. A suitable functionalization of the metalloporphyrin framework by deliberate synthesis can be effectively used to direct the spontaneous build-up of the porphyrin lattice by molecular recognition, and to construct structurally robust porous organic crystals with a desired architecture.

Over the last few years various metalloporphyrin macrocycles functionalized with potential hydrogen bond formers, metal coordinating ligands and polar groups have been successfully assembled into supramolecular lattices in our laboratory. [1] The basic motifs which compose these solids include hollow architectures of homogeneous porphyrin networks as well as of homo- and heterogeneous coordination polymers with varying dimensionality. The open aggregation modes give rise to the incorporation of suitably sized guest components into the crystal, the lattice cavity dimensions being affected by the type and shape of the interacting functional groups and axial ligands. Representative crystalline materials based on controlled multiporphyrin aggregation via either lateral associations sustained by hydrogen bonds or axial coordination polymerization propagated through the metal centers will be discussed in some detail, demonstrating the effectiveness of this approach to regulating the structural features of the interporphyrin assembly. Combination of these two plausible modes of supramolecular design is likely to yield in the future new materials with high structural integrity, and with better defined porosity and guest selectivity than in common clathrates.

1. R. Krishna Kumar, S. Balasubramanian and I. Goldberg, Inorg. Chem. 37 (1998), 541-552, and references cited therein.