Crystal inclusion chemistry of zinc-tetra(4-bromophenyl)porphyrin

Abstract

The structural patterns of Zn(II)-tetra(4-bromophenyl)porphyrin and several of its newly prepared complexes and clathrates in the solid phase were determined by X-ray crystallography. The molecular structure of the porphyrin compound is characterized by a nearly perfect planarity of the metalloporphyrin core due to effective Zn...;Br intermolecular interactions in the crystalline lattice. The composite materials show three different kinds of interporphyrin organization, dominated to a large extent by the molecular shape, often exhibited by related tetraphenylporphyrin derivatives. These include monoclinic ‘herringbone’ packing modes without any apparent involvement of the halogen atoms in specific interactions, chained interporphyrin arrangements exhibiting C-Br...;π close approach, and porous layered networks of the porphyrin species revealing direct Br...;Br contacts. The latter two forms are also affected by C-H...;Br attractions. Four-, five- and six-coordination of the central zinc ion was observed, but there is no apparent correlation between the coordination number and the crystal packing type. Thermal analysis revealed the relative strength of binding of the ligand and solvate species to the porphyrin lattice. The bromophenyl-substituted porphyrin building block forms only a small number of crystalline heteromolecular materials with other components, and occurrence of the uniquely structured porous porphyrin networks is not as dominant as in the analogous chlorophenyl derivatives. Estimates of interporphyrin packing stabilization energies suggest that the stability of these layered patterns is affected primarily by dipolar attractions, which are less significant in solids containing the Br, rather than Cl, groups.