Supramolecular assembly of functionalized metalloporphyrins. Porous crystalline networks of Zinc-tetra(4-carboxyphenyl) porphyrin

Abstract

Two crystalline compounds based on the Zn-tetra (4-carboxyphenyl)porphyrin building block have been prepared and structurally analysed by x-ray diffraction in order to ellucidate the characteristic supramolecular aggregation modes of this functionalized metalloporphyrin moiety. Crystals of the 1:1 complex with sec-phenethyl alcohol (1) are monoclinic, space group I2/a (No. 15), a = 14.420(1), b = 24.678(2), c = 33.688(2) Å, β = 90.03(2)°, D_c = 1.082 g/cm³, Z = 8, R = 0.080 for 3053 data. Those of the 1:3 complex with dimethylsulphoxide (2) are monoclinic, space group P2₁/n (No. 14), a = 14.881(1), b = 8.986(2), c = 37.550(3) Å, β = 94.21(1)°, D_c = 1.444 g/cm³, Z = 4, R = 0.093 for 4200 data. The two compounds consist of nearly square-pyramidal five-coordinate metalloporphyrin species, molecules of the sec-phenethyl alcohol (in 1) and dimethylsulphoxide (in 2) linking to the metal center at the axial site. In 2, two additional molecules of dimethylsulphoxide associate through H-bonds to the terminal carboxylic substituents of the porphyrin framework. Incorporation of the carboxylic functionality into the tetraarylporphyrin unit leads to the formation of hollow hydrogen-bonded lattices in both crystals. Uniquely structured two-dimensional networks of the porphyrin building blocks with very large cavities (approximately 16 × 21 Å) are formed in 1. These networks mutually interpenetrate each other in order to fill the empty voids, yielding a spectacular ‘concatenated’ arrangement. One-dimensional polymeric patterns with smaller cavities (6.5 × 10 Å) are built in 2 by the interacting molecular components. In the condensed crystalline environment each such cavity is occupied by two dimethylsulphoxide molecules of adjacent chains. This study is part of an ongoing evaluation of the utility of functionalized metalloporphyrin building blocks in the designed construction of hollow lattices (with varying degree of rigidity and pore size) in molecular based solids. Correlation of current results to previous findings is also discussed.