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

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.