Host-Guest Interactions Facilitated by Chalcogen Bonding within Selenadiazole Functionalised Porphyrin Nanotubes

The structural rigidity of tetrakis(4-pyridyl)porphyrin (TPyP) has been utilised to prepare a robust novel porous coordination polymer of composition Cd₂(TPyP)(sez)₂ (TPyP=5,10,15,20-tetra(4-pyridyl)porphyrin, sez=1,2,5-benzoselenadiazole-5-carboxylate). The coordination polymer may be described as a hexagonal porphyrin nanotube (PNT) and has the potential to bind guest molecules through chalcogen bonding. Single crystal X-ray diffraction (SCXRD) data indicate an internal pore diameter ~9 Å which represents ~35 % of the crystal volume. Immersion of the PNTs in solvents such as DMSO and CS₂ result in the incorporation of these molecules within the nanotubes with chalcogen bonding between host and guest. The crystallographic guest-inclusion investigations are complemented by solid-state ⁷⁷Se, ¹³C, ¹¹³Cd and ²H NMR studies which provide insights into dynamic behaviour. The porosity of the crystals was further explored using gas adsorption experiments, indicating the reversible uptake of CO₂, CH₄, H₂ and N₂. Structure-function relationships are clearly established from complementary crystallographic, NMR and adsorption investigations.