Porphyrin sieves. Designing open networks of tetra(carboxyphenyl)porphyrins by extended coordination through sodium ion auxiliaries

Abstract

The structural features of two- and three-dimensional multiporphyrin coordination polymers in which the free base and zinc-metallated tetra(4-carboxyphenyl)porphyrin (TCPP and ZnTCPP, respectively) building blocks are tessellated by sodium ion auxiliaries have been evaluated. These network arrays are stabilized primarily by ion-pairing forces, exhibiting diverse sodium–poly(carboxylic/carboxylate) interaction synthons. The observed structures reveal a common basic motif of a layered organization of the porphyrin species with void spaces between them. In order to optimize multiple coordination of the carboxyphenylporphyrins to the sodium ions these layers stack one on top of the other in a parallel fashion, with the ions located between them. The resulting lattices thus resemble molecular sieve materials, as they all contain spacious channels (their van der Waals cross-section varying from 3 to 6 Å) which propagate through the stacked layers and entrap other molecules. Structures involving the non-metallated TCPP building blocks contain additional channel cavities that extend between the porphyrin layers. The channel voids of both types account for 28–40% of the crystal volume (the upper range referring to the TCPP-based materials), depending on the structural and compositional modifications incorporated into the component species and reaction mixtures. The results provide new insights into the designed formulation of structurally rigid multiporphyrin arrays.