Crystal engineering of molecular networks: Tailoring hydrogen-bonding self-assembly of tin-tetrapyridylporphyrins with multidentate carboxylic acids as axial ligands

This study reveals the self-assembly patterns of six-coordinate complexes of the tetra(4-pyridyl)- and tetra(3-pyriyl)-tin-porphyrin moieties (SnT ⁴PyP and SnT³PyP, respectively) with multidentate carboxylic acids as axial ligands. Detailed structural characterization of the supramolecular organization in the resulting ordered solids by X-ray diffraction is reported. Crystals of the five new Sn(acid)2-TPyP complexes consist of multiporphyrin polymeric chains and networks that are sustained by extensive hydrogen bonding, involving the functional substituents on the axial ligands as proton donors and the peripheral N-sites of the porphyrin as proton acceptors. The use of different ligands leads to different connectivity features of the supramolecular assemblies that form. Structures with the 5-hydroxyisophthalic acid and trimesic acid ligands (1 and 2) reveal the formation of one-dimensional hydrogen-bonded chains only, as solvation effects prevent interporphyrin interaction in other directions. Reaction of the tin-porphyrin with 5-amino-isophthalic acid yielded a two-dimensional hydrogen-bonding network (3), while the reaction products with cis- 1,3,5-cyclohexane-tricarboxylic acid (4) and 5-bromo-isophthalic acid (5) are characterized by three-dimensionally interlinked assemblies. The above examples highlight the pronounced effect of the axial ligands (A) on the hydrogen-bonding-driven supramolecular aggregation of the Sn(A)₂-TPyP building blocks in crystals.