Artefact-free broadband 2D NMR for separation of quadrupolar and paramagnetic shift interactions

Two new two-dimensional, broadband, solid-state NMR experiments for separating and correlating the quadrupolar and shift interactions of spin I=1 nuclei in paramagnetic systems are proposed. The new pulse sequences incorporate the short, high-power adiabatic pulses (SHAPs) into the shifting d-echo experiment of Walder et al. [J. Chem. Phys., 142, 014201 (2015)], in two different ways, giving double and quadruple adiabatic shifting d-echo sequences. These new experiments have the advantage over previous methods of both suppressing spectral artefacts due to pulse imperfections, and exhibiting a broader excitation bandwidth. Both experiments are analysed with theoretical calculations and simulations, and are applied experimentally to the ²H NMR of deuterated CuCl₂ ⋅2H₂O, and two deuterated samples of the ion conductor oxyhydride BaTiO_3-xH_y prepared using two different methods. For the CuCl₂ ⋅2H₂O sample, both new methods obtain very high-quality spectra from which the parameters describing the shift and quadrupolar interaction tensors, and their relative orientation, were extracted. The two BaTiO_3-xH_y samples exhibited different local hydride environments with different tensor parameters. The ²H spectra of these oxyhydrides exhibit inhomogeneous broadening of the ²H shifts, and so whilst the quadrupolar interaction parameters were easily extracted, the measurement of the shift parameters was more complex. However, effective shift parameters were extracted, which combine the effects of both the paramagnetic shift tensor and the inhomogeneous broadening.