Unraveling the Complex Hydrogen Bonding of a Dual-Functionality Proton Conductor Using Ultrafast Magic Angle Spinning NMR

Abstract

Hydrogen bonding plays a critical role in proton-conducting polymers, as it provides the network necessary for structural (Grotthus mechanism) diffusion. This network must be both pervasive and dynamic in order for long-range proton transport to be achieved. The structural motifs must be understood, even in amorphous materials, and moreover, the lattice energies in the structure must be low enough to allow rearrangement and mobility. To this end, a novel proton-conducting candidate, 1,10-(1-H-imidazol-5-yl)decanephosphonic acid and its HBr doped counterpart are considered from the molecular level as potential proton-conducting membranes. The use of high-resolution solid-state 1H NMR to elucidate structure and dynamics of such systems is highlighted in this material. We compare our molecular-level results to macroscopic probes of proton transport in related polymers, achieved using impedance spectroscopy.

Investigation of proton dynamics and the proton transport pathway in choline dihydrogen phosphate using solid-state NMR

“…Proton double-quantum filtered ( 1 H DQF) experiments have been used in the study of a large number of systems for determination of the packing arrangement of the hydrogen-bonding motifs. [6][7][8][9][10][11] These experiments access the information inherent to through-space dipolar coupling and the relative strength of the measured dipolar coupling can be used as a probe of molecular mobility.…”

Recent Advances in Solid‐State MAS NMR Methodology for Probing Structure and Dynamics in Polymeric and Supramolecular Systems

“…This shifting of the phases achieves a negation of the spin-part of the DQ Hamiltonian, which exactly compensates the negation of the spatial part caused by MAS. [7,13] The BABA sequence was used initially in the context of a heteronuclear 13 C-1 H MQ coherence experiment, [12] and was adapted for homonuclear 31 P DQ MAS experiments, [14,15] with modified two-and four-t R versions having been employed, which provide compensation with respect to offset and pulse imperfections. [16] The first application of the BABA recoupling sequence in 1 H DQ MAS spectroscopy coincided with the first 1 H DQ MAS experiments at 35 kHz MAS using a 2.5 mm MAS probe.…”

“….O S. P. Brown proton proximities in a range of other hydrogen-bonded systems, for example, bilirubin, [22] polyelectrolyte complexes, [23][24][25] self-assembled monolayers formed by diacids adsorbed on nanocrystalline TiO 2 and ZrO 2 , [26] keto-enol tautomerism [7,[27][28][29] and proton-conducting materials. [30][31][32][33] Aromatic Ring Current Effects in Hexabenzocoronene (HBC [34] of the solid phase of an alkyl-substituted HBC, [35] HBC-(CD 2 )C 11 -the notation refers to all six R substituents being 12-carbon n-dodecyl alkyl chains, with the sample having been synthesised with the a-carbons deuterated (87%) in order to carry out 2 H NMR. Considering the individual molecules alone (and assuming full conformational flexibility of the R alkyl groups), the effective sixfold symmetry of the aromatic core means that only one distinct aromatic proton resonance is expected, as is indeed found to be the case in the solution-state 1 H spectrum (not shown).…”

“…The spin-echo MAS technique has been applied widely, in particular for the 100% natural abundant 31 P nucleus in inorganic chemistry and materials applications. [171,172,[175][176][177][178][179][180][181][182][183] Recently, the spin-echo experiment has been applied to organic systems.…”

Solid-state NMR studies of hydrogen bonding networks and proton transport pathways based on anion and cation dynamics

“…Fast magic angle spinning (MAS) is particularly valuable in achieving spectral resolution of 1 H NMR spectra in the solid-state, where the extensive homonuclear dipolar coupling network causes severe line broadening. 16,17 Building upon the standard 1 H MAS NMR spectra, the full connectivity of the individual protons can be established via the 2D double quantum (DQ) pulse sequence, which is used to map out all the homonuclear dipolar coupled spin pairs in the material. 18 -20 The key advantage of 2D DQ MAS NMR for structural analysis is that the materials do not have to be crystalline to observe the connectivity of the different resonances in the spectrum.…”