Solid-state supramolecular chemistry of porphyrins. Ligand-bridged tetraphenylmetalloporphyrin dimers

Eight new crystalline materials based on ligand-bridged dimers of either Zn(II)- or Co(II)-tetraphenylporphyrins have been prepared and characterized by X-ray diffraction analysis. These supramolecular entities have a "wheel-and-axle'' type shape, the elongated bidentate ligands 1,3-diaminopropane, 1,4-diaminobutane, 4,4'-bipyridyl, 1,2- bis(4-pyridyl)ethene or 1,2- bis(4-pyridyl)ethane coordinating axially on both sides to the metal centers of the porphyrin species. They vary from one another by the length of the ligand spacer, the distance between the two porphyrin components ranging from 9.4 Angstrom to 14.0 Angstrom. The intermolecular organization in these structures is characterized by a similar chain motif in which adjacent oligomeric units interlock into one another. In spite of the steric constraint imposed by the bridging ligand, this packing preserves the typical corrugated stacked arrangement of the porphyrin frameworks which has been commonly observed in clathrates of monomeric tetraarylporphyrins. It also induces in most cases large voids between the interlocked motifs, causing enclathration of solvent molecules in the crystal lattice. The experimentally established geometries of these oligomers and their crystal packing modes provide useful information for further crystal engineering efforts of polymeric multiporphyrin domains.