Dynamics of Molecular Crystals by Means of ¹H NMR Relaxometry: Dynamical Heterogeneity versus Homogenous Motion

Abstract

(1) H NMR relaxometry was used to reveal information on the dynamical properties of the molecular crystal (PyH)5 Bi2 Br11 (PyH=C5 H6 N, pyridinium cation), chosen as an example of a solid that exhibits a complex structure and rotational-like dynamics. Experimental studies were performed over a very broad frequency range, from 4 kHz to 40 MHz (referring to the (1) H resonance frequency) versus temperature. The extensive set of data was thoroughly analyzed in terms of two motional models differing with respect to the assumed mechanism (heterogeneous versus homogenous) of the motion of the PyH cations. A Cole-Davidson distribution of the correlation times describing the assumed motional heterogeneity was tested against a concept of two correlation times characterizing the rotation-like dynamics of the PyH cation around the perpendicular axes differing by about one order of magnitude. The parameters describing the dynamics of the cation, obtained by means of both models, were compared and discussed.

Dynamics of Ionic Liquids in Confinement by Means of NMR Relaxometry—EMIM-FSI in a Silica Matrix as an Example

“…The relaxation contribution associated with the intra-cation 1 H– 1 H dipole–dipole interactions was interpreted in terms of two processes characterized by the parameters: , and , .One should explain at this stage that this concept could be replaced by another one—namely a heterogeneous dynamics described by a distribution of correlation times. Typically, the Cole–Davidson function [ 40 , 41 , 42 , 43 ] originating from dielectric spectroscopy is used for this purpose. The function includes a phenomenological parameter ( ).…”

Dynamics of Solid Proteins by Means of Nuclear Magnetic Resonance Relaxometry

“…Nuclear magnetic resonance relaxometry is one of the main methods providing information about molecular dynamics and structure [4,5,6,7,8]. Standard NMR relaxation experiments are performed only at a single relatively high magnetic field (resonance frequency), while fast field-cycling (FFC) NMR relaxometry [9,10] allows one to carry out relaxation studies in a remarkably broad frequency range encompassing five orders of magnitude, from approximately 1 kHz to 120 MHz (referring to 1 H resonance frequency).…”

“…Standard NMR relaxation experiments are performed only at a single relatively high magnetic field (resonance frequency), while fast field-cycling (FFC) NMR relaxometry [9,10] allows one to carry out relaxation studies in a remarkably broad frequency range encompassing five orders of magnitude, from approximately 1 kHz to 120 MHz (referring to 1 H resonance frequency). As a consequence, NMR relaxometry can detect motional processes across a broad range of time scales (from ms to ps) in a single experiment [4,5,6]. Moreover, frequency-dependent relaxation studies possess the exceptional potential to reveal the underlying mechanisms of molecular motion (not only its time scale) [4,5,8,11,12,13,14,15,16,17,18,19].…”

“…As a consequence, NMR relaxometry can detect motional processes across a broad range of time scales (from ms to ps) in a single experiment [4,5,6]. Moreover, frequency-dependent relaxation studies possess the exceptional potential to reveal the underlying mechanisms of molecular motion (not only its time scale) [4,5,8,11,12,13,14,15,16,17,18,19]. The dominant mechanism of 1 H relaxation is provided by magnetic dipole–dipole interactions.…”

Mechanistic Insights into Polyion Complex Associations

“…The measured 1 H relaxation rates are due to fluctuations in energy of the proton–proton dipole–dipole interactions and depend on the time constants of the motions modulating such interactions. Therefore, they can provide information on the characteristic time constants of such motions. − The profiles of DGL3 and the two block copolymers showed a single dispersion at high fields, corresponding to a correlation time of about 3 ns (Figure SI.3.1 in SI.3).…”