Dynamical processes and order behind the pronounced 1H NMR paramagnetic relaxation enhancement induced in [P6,6,6,14]3[GdCl6]-based ionic liquid mixtures

NMR relaxometry is a technique that allows the molecular dynamics study of chemical compounds across a broad time scale, ranging from slow translational diffusion or collective motions to fast rotations. The present work is a 1H NMR relaxometry and diffusometry study of systems based on [P6,6,6,14][Cl] and [P6,6,6,14]3[GdCl6] ionic liquids, complemented by X-ray diffractometry measurements. The use of the X-ray profiles enabled the determination of an almost temperature independent interdigitated disposition of the cations that is at the origin of local order fluctuations. This structure also affects the paramagnetic relaxation enhancement, which is very significant for these systems and is achieved at very low metal concentrations (around 1mM). The present study provides a comprehensive analysis that is consistent for all the analyzed systems and across the different experimental techniques, despite the experienced technical challenges related to extremely short relaxation times. Additionally, the Electrochemical Impedance Spectroscopy profiles of the neat [P6,6,6,14][Cl] sample were explained by an analogous equivalent circuit model that allowed for a global analysis consistent with the diffusometry and X-ray diffractometry results. The representation of the real and imaginary parts of the impedance allowed for a visual deconvolution of the contributions of the different circuit blocks considered in the model.

Descrição

The authors would like to thank European COST Action EURELAX CA15029 (2016-2020) and Carla I. Daniel for the initial contributions, namely providing the paramagnetic mixtures and measuring water content, and for allowing use of the setups to measure the systems density and viscosity. For enabling the diffusometry studies at 11.7T, the authors also acknowledge Maria Jo\u00E3o Ferreira and Jos\u00E9 Acenso for access to the CQE NMR laboratory at Instituto Superior T\u00E9cnico, Lisbon. M.C.C. gratefully acknowledges PTNMR for the researcher contract. This work was supported by Funda\u00E7\u00E3o para a Ci\u00EAncia e Tecnologia through projects: UID/DTP/04138/2020, UIDB/50025/2020-2023 and PTNMR (2017-2020); and European Commission project M-ERA-NET2/0006/2019 (2017-2020) CELLCOLOR. The NMR spectrometers at IST and FCT NOVA are part of the National NMR network (PTNMR). They are partially supported by Infrastructure Project no. 022161 (co-financed by FEDER through COMPETE 2020, POCI and PORL and FCT through PIDDAC). Publisher Copyright: © 2025 The Author(s)

Palavras-chave

H NMR relaxometry EIS Local order fluctuations Magnetic ionic liquids Molecular dynamics simulations Trihexyl(tetradecyl)phosphonium chloride Trihexyl(tetradecyl)phosphonium hexachlorogadolinium Wide angle X-ray Electronic, Optical and Magnetic Materials Atomic and Molecular Physics, and Optics Condensed Matter Physics Spectroscopy Physical and Theoretical Chemistry Materials Chemistry