Porphyrin framework solids. hybrid supramolecular assembly modes of tetrapyridylporphyrin and aqua nitrates of lanthanoid ions

New types of porphyrin-based framework solids were constructed by reacting meso-tetra(4-pyridyl)porphyrin (TPyP) with various aqua nitrate salts of lanthanoid metal ions [Ln(NO₃)₃(H₂O) _x]. They represent hybrid organic'inorganic crystalline compounds in which the tetradentate porphyrin units, having both coordination as well as hydrogen bonding functionalities, are interlinked through the inorganic connectors into self-assembled three-dimensional architectures. The lanthanoid complexes bear, in addition to the coordination capacity of the metal ions, multiple molecular recognition sites on their nitrate and water ligands, serving as effective linkers of the supramolecular arrays that form. Several different modes of the intermolecular association were revealed by single-crystal X-ray diffraction. They differ by the nature of the interaction synthons between the component species, the degree of protonation of the porphyrin entities in the given experimental conditions, and the topology of the resulting assemblies. An exceptional structure, in which a doubly protonated porphyrin unit and the lanthanoid species formed separate hydrogen bonded arrays (where one-dimensional chains of the latter are enclathrated within two-dimensional layers of the former) by reacting the meso-tetra(3-pyridyl)porphyrin (TPy⁽³⁾P) with a dehydrated La-salt, is described as well. All the compounds are characterized by open architectures, giving rise to lattice-inclusion of solvent species. This study demonstrates that the TPyP building block may effectively engage in supramolecular constructs with the lanthanoid metal ions, either through direct coordination to the metal center and/or by hydrogen bonding to its coordination sphere ligands.