NMR chemical shifts of urea loaded copper benzoate. A joint solid-state NMR and DFT study

We thank EaStCHEM and the School of Chemistry for support. Computations were carried out on a local Opteron PC cluster maintained by Dr. H. Früchtl. This work was supported by the EPSRC through the Collaborative Computational Project on NMR Crystallography (CCP-NC), via EP/M022501/1. SEA would also like to thank the Royal Society and Wolfson Foundation for a merit award. ZK gratefully appreciates a scholarship from the China Scholarship Council (CSC).We report solid-state 13C NMR spectra of urea-loaded copper benzoate, Cu2(C6H5CO2)4.2(urea), a simplified model for copper paddlewheel-based metal-organic frameworks (MOFs), along with first-principles density functional theory (DFT) computation of the paramagnetic NMR (pNMR) chemical shifts. Assuming a Boltzmann distribution between a diamagnetic open-shell singlet ground state (in a broken-symmetry Kohn-Sham DFT description) and an excited triplet state, the observed δ(13C) values are reproduced reasonably well at the PBE0-⅓/IGLO-II//PBE0-D3/AE1 level. Using the proposed assignments of the signals, the mean absolute deviation between computed and observed 13C chemical shifts is below 30 ppm over a range of more than 1100 ppm.PostprintPeer reviewe