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

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.