Triptycene-Based Metal Salphens-Exploiting Intrinsic Molecular Porosity for Gas Storage

A series of triptycene-based molecules that have high measurable porosities in the solid state arising solely from their internal molecular free volume (IMFV) were reported. To perform a systematic study on the effect of IMFV on porosity, a series of compounds were developed with easily varied structures based on nickel salphen. The complexes can be easily synthesized in a one-pot reaction through Schiff base condensation. Thermogravimetric analysis (TGA) indicated that all of the molecules are stable to over 300°C and most to over 450°C. The effect of different molecular structures on porosity was quantified by using gas adsorption to measure accessible surface area and pore sizes in the molecular solids. Pore size distributions using Horvath-Kawazoe and BJH analyses were obtained and clearly show that these materials are predominantly microporous. Powder X-ray diffraction shows that most of the salphens retain some crystallinity after solvent removal.