Assessment of Adsorbate π-backbonding in Copper(I) Metal-Organic Frameworks via Multinuclear NMR Spectroscopy and Density Functional Theory Calculations

We assess the binding of C2H4 to the coordinately unsaturated copper(I) sites of the metal-organic frameworks Cu(I)-ZrTpmC* and Cu(I)-MFU-4l via 13C solid-state nuclear magnetic resonance spectroscopy, density functional theory (DFT), and natural localized molecular orbital (NLMO) analysis. Using these methods, forward-donation and back-donation contributions between C2H4 and the exposed Cu(I) are delineated and high-binding enthalpies are contextualized as a function of electronic changes upon site modification and adsorption. With the infrastructure for DFT and solid-state 13C NMR becoming more routine for scientists, we envision these results will support the study of exposed electron-rich metal sites in a variety of chemical applications.