Elucidating the Structure of the Metal-Organic Framework Ru-HKUST-1

Abstract

Ru-HKUST-1 (${\text{Ru}}_3{\left(\text{btc}\right)}_2{\text{X}}_{1.5};{\text{btc}}^{3-}=1,3,5\text{-benzenetricarboxylate}$; ${\text{X}}^{-}=\text{chloride},\text{acetate},\text{trimesate},\text{hydroxide}$) has received considerable attention as a result of its structure type, tunability, and the redox-active nature of its constituent metal paddlewheel building units. As compared to some of the other members of the HKUST-1 family, its surface area is typically reported as ~25% lower than expected. In contrast to this, a related ruthenium-based porous coordination cage, ${\text{Ru}}_{24}{{(}^{\text{t}}\text{Bu-bdc})}_{24}{\text{Cl}}_{12}$, displays the expected surface area when compared to ${\text{Cr}}^{2+}$ and ${\text{Mo}}^{2+}$ analogs. Here, we examine the factors that result in this decreased surface area for the MOF. We show that with appropriate solvent exchange and activation conditions, Ru-HKUST-1 can display a B.E.T. surface areas as high as 1439 m²/g. We utilize a combination of spectroscopic and diffraction techniques to accurately determine the structure of the MOF, which is most accurately described here as ${\text{Ru}}_3{\left(\text{btc}\right)}_2{\left(\text{OAc}\right)}_{1.07}{\text{Cl}}_{0.43}$, as prepared under our conditions. Further, by simply treating the sample as air-sensitive upon isolation, adsorption selectivities toward unsaturated molecu les greatly improve.