Adsorption of Olefins at Cupric Ions in Metal–Organic Framework HKUST-1 Explored by Hyperfine Spectroscopy

Abstract

Metal–organic frameworks (MOFs) represent a promising platform for gas storage and separation. In this work, adsorption of olefins in Zn-doped HKUST-1 metal–organic framework is explored with hyperfine spectroscopy. By means of electron–nuclear double resonance and hyperfine sublevel correlation spectroscopy, we detect the interaction between the electron spins of the Cu2+ sites of the MOF and the 1H nuclear spins of adsorbed C2H4 and C4H8. Further analysis of the measured spectra allows us to precisely locate the protons in the vicinity of the Cu2+ ions and thereby establish ensemble-averaged structural models of the olefin molecules adsorbed at the open metal sites of HKUST-1.

Structural and Hydrolytic Stability of Coordinatively Unsaturated Metal–Organic Frameworks M3(BTC)2 (M = Cu, Co, Mn, Ni, and Zn): A Combined DFT and Experimental Study

“…21−25 These as-synthesized isotypic MOF materials have been used in the gas adsorption and separation and various heterogeneous Lewis acid-catalyzed reactions. 17,21,23,26,27 For example, Kramer et al successfully synthesized Mo 3 (BTC) 2 with a high specific micropore volume and Brunauer−Emmett−Teller (BET) surface area for hydrogen adsorption capacity. 21 Long and his co-workers found the reversible, selective binding of O 2 at a high loading capacity within Cr 3 (BTC) 2 .…”

“…One of the most promising and widely studied MOFs containing CUSs is Cu 3 (BTC) 2 , which is also known as HKUST-1, where BTC is benzene-1,3,5-tricarboxylate, as illustrated in Figure a. Cu 3 (BTC) 2 is an ideal material for adsorbing toxic gases and heterogeneous catalysis, due to the Cu 2+ CUSs at the paddlewheel Cu–Cu node. − Previous studies show that the Cu–Cu node sites can be substituted by other metals (M) such as chromium (Cr), nickel (Ni), zinc (Zn), iron (Fe), and molybdenum (Mo) to form the isostructural metal-substitution analogues of M 3 (BTC) 2 . − These as-synthesized isotypic MOF materials have been used in the gas adsorption and separation and various heterogeneous Lewis acid-catalyzed reactions. ,,,, For example, Kramer et al successfully synthesized Mo 3 (BTC) 2 with a high specific micropore volume and Brunauer–Emmett–Teller (BET) surface area for hydrogen adsorption capacity . Long and his co-workers found the reversible, selective binding of O 2 at a high loading capacity within Cr 3 (BTC) 2 .…”

Atomic-Scale Quantum Sensing of Ensembles of Guest Molecules in a Metal–Organic Framework with Intrinsic Electron Spin Centers

“…(d) The contribution of the ensemble of 1 H nuclear spins to the stimulated spin echo intensity is resolved by scanning the frequency of the mixing RF pulse with the magnetic field set at the EPR transitions of z || B (left) and z ⊥ B (right) sensor orientations. The sharp features common for the empty and gas-loaded samples are due to the framework 1 H spins, whereas the broad line detected in the presence of butane is associated with the 1 H spins of the guest molecules.…”

“…In Figure d, the ENDOR spectra of the empty framework exhibits only the HF couplings with 1 H nuclei that belong to the benzene-1,3,5-tricarboxylate (btc) units of the MOF (for detail, see our previous work and Figure S3). In the presence of butane, however, these narrow HF features are superimposed with a broad intense line indicating the presence of additional 1 H nuclei in the vicinity of the Cu 2+ spin center.…”

“…Unlike diamond and other semiconductor materials, MOFs inherently have an extremely large inner surface area and thus can host abundant sensor sites. Pioneering experiments with paramagnetic metal ions acting as quantum sensors incorporated in the structure of MOF have demonstrated nanoscale magnetic detection of nuclear spins of adsorbed gas molecules. − These works, however, focused on guest molecules that have specific chemical affinity toward the sensing ion and are thus adsorbed exactly at the sensor site. In contrast, here we explore the case when the MOF inner surface and the sensor site are chemically inert with respect to the target molecular species.…”