1H NMR relaxometry and quadrupole relaxation enhancement as a sensitive probe of dynamical properties of solids—[C(NH2)3]3Bi2I9 as an example

Abstract

(1)H nuclear magnetic resonance relaxometry has been applied to reveal information on dynamics and structure of Gu3Bi2I9 ([Gu = C(NH2)3] denotes guanidinium cation). The data have been analyzed in terms of a theory of quadrupole relaxation enhancement, which has been extended here by including effects associated with quadrupole ((14)N) spin relaxation caused by a fast fluctuating component of the electric field gradient tensor. Two motional processes have been identified: a slow one occurring on a timescale of about 8 × 10(-6) s which has turned out to be (almost) temperature independent, and a fast process in the range of 10(-9) s. From the (1)H-(14)N relaxation contribution (that shows "quadrupole peaks") the quadrupole parameters, which are a fingerprint of the arrangement of the anionic network, have been determined. It has been demonstrated that the magnitude of the quadrupole coupling considerably changes with temperature and the changes are not caused by phase transitions. At the same time, it has been shown that there is no evidence of abrupt changes in the cationic dynamics and the anionic substructure upon the phase transitions.

209Bi quadrupole relaxation enhancement in solids as a step towards new contrast mechanisms in magnetic resonance imaging

“…[20][21][22][23][24][25][26][27][28] For 14 N one observes three relaxation maxima. [20][21][22][23][24][25][26][27][28][29][30] As far as higher spin quantum number quadrupole nuclei are concerned, there are some indications of the QRE effects in LaF 3 . 31,32 In this context the question arises whether QRE can be exploited as a mechanism for novel extrinsic MRI contrast agents.…”

Aspects of structural order in 209Bi-containing particles for potential MRI contrast agents based on quadrupole enhanced relaxation

“…This process can only occur at magnetic fields at which the proton resonance frequency matches one of the transition frequencies of the QN between its energy levels. It manifests itself as a fast decay of the proton magnetisation interpreted as an enhanced spin-lattice relaxation rate R 1 = 1/T 1 [1][2][3][4][5][6][7][8] referred to as quadrupole peaks. The position of the quadrupole peaks is a function of the static magnetic field B 0 , the electric field gradient (EFG) at the location of the nucleus, the electrical quadrupole moment of the QN, its spin quantum number I and the angle Θ between EFG and B 0 [1][2][3][4][5][6][7][8][9][10][11].…”

“…The most special feature is that, in contrast to typical paramagnetic MRI contrast agents, [12][13][14][15][16] QRE leads to narrow peaks and steep slopes [1,2,4,5,[8][9][10][11]. In fact, such QRE peaks were observed for 14 N in the amide groups of proteins [17][18][19] and used for the first time for MRI contrast at very low B 0 [20] in humans.…”

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

“…One should, however, note that even though the relaxation constants and for model I vary with temperature, their sum, , remains temperature independent. This can be explained by treating the intermediate and fast processes as two steps of the Lipari–Szabo model of motion . According to this model, fast, but anisotropic, motion leads to the first step of the decay of the time correlation function describing the fluctuations of the dipole–dipole interaction.…”