Heteromolecular grids of free-base and zinc-tetra(4-pyridyl)porphyrins with benzenetetracarboxylic acid

This study describes the formation of hetero-molecular networks involving the 1,2,4,5-benzenetetracarboxylic acid (BTCA) and either the free-base or zinc-metallated tetra(4-pyridyl)porphyrin (TPyP or Zn–TPyP, respectively), taking advantage of the complementary tetradentate H-atom donor and H-atom acceptor capacity of the component species. The reaction of BTCA with TPyP yields flat square-grid-type hydrogen bonded arrays, wherein every BTCA moiety interacts with four different porphyrin units and each one of the latter links laterally to four different tetraacid molecules. Replacement of TPyP by Zn–TPyP adds axial coordination capacity to the porphyrin unit and changes the intermolecular interaction pattern. In this case, the supramolecular self-assembly involves trans-axial coordination of BTCA to Zn–TPyP, into a 2:1 complex of the two species, as well as extended hydrogen bonding in four lateral directions between the (BTCA)₂(Zn–TPyP) units thus formed. The hydrogen-bond networking takes place between the four N(pyridyl)-sites of the porphyrin scaffold and the axial tetracid ligands of four neighboring complexes. In the two crystals, the open hydrogen bonded molecular networks stack in an offset manner, incorporating molecules of the 1,1,2,2-tetrachloroethane solvent within channel zones that penetrate through the layered structure. Application of the TPyP scaffold in the formation of hydrogen-bonded (rather than coordination-driven) assemblies has not been explored prior to our work on this subject.