Proton-detected fast-magic-angle spinning NMR of paramagnetic inorganic solids

Abstract

Fast magic-angle spinning NMR allows rapid fingerprinting of paramagnetic organometallic complexes in powder form.

Electron correlation and vibrational effects in predictions of paramagnetic NMR shifts

“…However, due to limitations of DFT approximations, the practice of making arbitrary HFX parameter adjustments to increase the agreement between calculated and experimentally observed NMR shifts in paramagnetic systems has recently evolved. 65,66 Such calculations use the ''standard'' PBE0 functional and ''modified'' ones (with HFX fractions up to 50%) with the hope that the HFCCs obtained would describe the paramagnetic NMR shifts observed experimentally. Due to the nature of chemical bonding, the optimal HFX will vary even among different elements and atomic positions within the same molecule, greatly limiting the predictive power for signal assignments, etc.…”

Multidimensional Methods and Paramagnetic NMR

“…With the use of faster MAS it becomes possible to observe the 1 H spectrum directly, via a version of the TEDOR sequence with indirect detection, which benefits from the higher sensitivity of observing the nucleus with the larger γ I (HSQC-TEDOR) [31,32] . The uniformly short T 1 relaxation times observed in a paramagnetic solid sample, together with the absence of the requirement for high-power RF irradiations during the experiment, allow the use of very short recycle delays between acquisitions.…”

“…The HSQC-TEDOR was recently employed for the characterisation of a Fe(II) organometallic complex [32] and a metallo-organic framework containing Ni(II) paddle-wheel units [29] , where 2D correlation can be acquired within 30 minutes on 1-2 mg of samples at natural 13 C abundance. Depending on the recoupling period employed, 1 H-13 C correlations can be observed either over short distances corresponding to a single bond, or over longer distances, including correlations between 1 Hs and quaternary 13 Cs (Figure 1.9 (d)).…”