Supramolecular architectures of functionalized tetraphenylmetalloporphyrins in crystalline solids. Studies of the 4-methoxyphenyl, 4-hydroxyphenyl and 4-chlorophenyl derivatives

Abstract

A series of new ‘inclusion’ materials based on tetra-4-methoxyphenyl, tetra-4-hydroxyphenyl and tetra-4-chlorophenyl derivatives of the metalloporphyrin system, in combination with a wide variety of guest molecules and ligands, have been prepared, and their structural systematics analysed. Crystallographic investigations have confirmed that the supramolecular arrangement of the hydroxyphenylporphyrin species is dominated by interporphyrin directional hydrogen-bonding interactions, and consists of continuous networks of strongly coordinated entities with varying degrees of cross-linking and rigidity. Guest molecules can be absorbed in these solids in distinctly defined sites of the lattice: in the small interhost cages of fixed size between adjacent intercoordinated porphyrin hosts, or in extended one-dimensional channels formed between the hydrogen bonded host arrays running parallel or perpendicular to the porphyrin plane. For polar ligands with strong nucleophiles, their potential coordination to the metal center provides an additional recognition factor. The stacking mode (offset geometry or overlapping) of the host metalloporphyrin arrays is also affected by the nature of the incorporated guest/ligand. Materials based on the chloro-substituted porphyrins were found to form similarly networked structural modes, influenced by the molecular shape as well as by halogen-halogen noncovalent interactions. Formation of a polar tubular intermolecular architecture capable of aligning organic dipolar guest molecule in the crystal bulk has also been demonstrated. The methoxy-substituted materials form clathrate-type structures characterized by dense layered arrangement of the porphyrin building blocks in two-dimensions. The various structural features directing the observed modes of the supramolecular architecture, and affecting the host structure as well as the guest mobility in it, are discussed.