CRYSTAL INCLUSION CHEMISTRY OF ZINC-TETRA(4-BROMOPHENYL)PORPHYRIN

The structural patterns of Zn(II)-tetra(4-bromophenyl)porphyrin and se veral of its newly prepared complexes and clathrates in the solid phas e 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 in teractions in the crystalline lattice. The composite materials show th ree different kinds of interporphyrin organization, dominated to a lar ge extent by the molecular shape, often exhibited by related tetraphen ylporphyrin derivatives. These include monoclinic 'herringbone' packin g modes without any apparent involvement of the halogen atoms in speci fic interactions, chained interporphyrin arrangements exhibiting C-Br ...pi close approach, and porous layered networks of the porphyrin spe cies revealing direct Br ... Br contacts. The latter two forms are als o affected by C-H ... Br attractions. Four-, five- and six-coordinatio n of the central zinc ion was observed, but there is no apparent corre lation between the coordination number and the crystal packing type. T hermal analysis revealed the relative strength of binding of the ligan d and solvate species to the porphyrin lattice. The bromophenyl-substi tuted porphyrin building block forms only a small number of crystallin e heteromolecular materials with other components, and occurrence of t he uniquely structured porous porphyrin networks is not as dominant as in the analogous chlorophenyl derivatives. Estimates of interporphyri n packing stabilization energies suggest that the stability of these l ayered patterns is affected primarily by dipolar attractions, which ar e less significant in solids containing the Br, rather than Cl, groups .