Coordination Polymers of Tetra(4-carboxyphenyl)porphyrins Sustained by Tetrahedral Zinc Ion Linkers

Abstract

Reactions between the free base tetra(4-carboxyphenyl)porphyrin and the corresponding platinum or palladium metalloporphyrin derivatives with zinc acetate dihydrate under solvothermal conditions in a basic environment (in the presence of pyridine and ammonium hydroxide) yielded extended supramolecular networks. These polymeric arrays consist of fully deprotonated porphyrin carboxylate units interconnected to each other by Zn(H2O)22+ auxiliaries. The zinc ion linkers adapt a tetrahedral coordination environment, imparting to the polymeric network an open three-dimensional architecture, wherein each zinc binds to two adjacent porphyrin units and two water ligands, while every porphyrin entity is linked to four different metal centers. In a reaction involving the free base macrocycle, the zinc ions were inserted into the porphyrin core as well, forming a five-coordinate entity with pyridine as an axial ligand. The solid state syntheses yielded either one-dimensional ladder type coordination polymers that pair in an interlocking manner or three-dimensional diamondoid arrangements with interpenetrating polymeric networks. Both types of frameworks are further interlinked to each other by weak hydrogen bonds from the zinc-bound water ligands of one array to the carboxylate functions of another. The previously reported porphyrin-based polymer tessellated by Zn2+ linkers that coordinate at a given binding site to four (rather than two) porphyrin units is also discussed.