In order for natural gas to be utilized in the transportation sector its volumetric energy density must be increased. This is typically done via liquefaction or high pressure storage, both processes that require high energy input. Current alternatives to these include adsorptive storage with the appropriate solid adsorbent. Metal-organic frameworks have shown considerable promise in this regard. Gas adsorption phenomena in metal-organic frameworks has been well documented through computational and diffraction studies to determine gas adsorption sites within these porous materials. In particular, HKUST-1 has been known to adsorb methane at high pressures in a triangular pore but much of the framework has void space diminishing its potential for high pressure methane storage. Via precise molecular design, this pore has been isolated in the porous molecular cage Mo_DTolF_btc (DTolF=ditolyl-formamidine, btc=benzenetricarboxylate). The cages are composed of molecular capping units by the bridging formamidine groups and organic ligands with three carboxylate groups to bind to the available coordination sites on the metal to make cages with six metal nodes and four bridging organic ligands. These compounds show solubility in a variety of organic solvents while maintaining their structure in solution. Structure determination has been performed through single crystal X-ray diffraction and NMR. TGA has been used to study the thermal stability of the compounds. The compounds are able to be desolvated while still maintaining porosity.  Gas adsorption isotherms indicate these materials display BET surface areas ranging from 400 to 2000 m<sup>2</sup>/g, depending on ligand capping group . The uptake properties of these compounds for CO<sub>2</sub>, ethane, acetylene, and methane have been studied. Additionally, due to the soluble nature of these porous cages, they have been able to be applied as thin films to a variety of surfaces for testing as sensors. As thin films, the material maintains its porosity and can adsorb a variety of gases and solvent vapors. Their utility as solvatochronic sensors will also be discussed.

Molybdenum-based porous molecular cages for gas storage and solvatochromic sensing

256th National Meeting (2018)

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