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

• Published in: Solid state nuclear magnetic resonance 2019-09, Vol.101, p.31-37
• Main Authors: Ke, Zhipeng, Jamieson, Lauren E., Dawson, Daniel M., Ashbrook, Sharon E., Bühl, Michael
• Format: Article
• Language: English
• ISSN: 0926-2040; 1527-3326
• DOI: 10.1016/j.ssnmr.2019.04.004

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. [Display omitted] •Cu(C6H5CO2)4·2(urea), a model for metal-organic frameworks, shows pNMR shifts for 13C.•The shifts stem from a triplet state in equilibrium with the singlet ground state.•Shifts are computed assuming a Boltzmann distribution of the two spin states.•Sign and magnitude of the pNMR shifts can be rationalised by the triplet spin density.