Coordination self-assembly through weak interactions in meso-dialkoxyphosphoryl-substituted zinc porphyrinates

Abstract

The self-assembly of seven zinc 10-(dialkoxyphosphoryl)-5,15-diarylporphyrinates Zn5–Zn11 containing different substituents at the phosphonate and aryl groups was investigated. Single crystals of Zn5–Zn9 complexes were grown under the same conditions and analyzed by X-ray structural analysis. A supramolecular self-assembly is observed in all crystals through weak coordinative bonding of the phosphoryl group of one porphyrin molecule to the zinc(II) ion of a second molecule. The geometry of the porphyrin macrocycle is similar in all of the studied crystals and the central zinc atom in each case adopts a distorted tetragonal pyramidal environment. However, the Zn5–Zn7 porphyrins display a 1D polymeric structure while the Zn8 and Zn9 complexes exist as discrete cyclotetramers in the crystals. This data demonstrates that the non-coordinating meso-aryl substituents of meso-(dialkoxyphosphoryl)porphyrins influence their crystalline organization. A self-assembly of the Zn5–Zn11 complexes is also observed in toluene and chloroform solutions over a large temperature range (223–323 K). According to NMR studies, the associates exhibit dynamic behavior. A well-defined supramolecular aggregate of complex Zn10 at 10⁻³ M in toluene and chloroform solutions was unambiguously characterized as a cyclotetramer [Zn10]₄ by ¹H NMR spectroscopy at 223 K. The structure of the Zn10 association in toluene and chloroform shows a concentration dependence. When a solution of Zn10 in toluene was diluted from 10⁻³ M to 10⁻⁵ M, the average number of molecules in the associated unit decreased to about two.