Structure and dynamics of [NH₂(CH₃)₂]₃Sb₂Cl₉ by means of ¹H NMR relaxometry – quadrupolar relaxation enhancement effects

Abstract

H spin-lattice relaxation experiments have been performed for [NH(CH)]SbCl (tris(dimethylammonium)nonachlorodiantimonate(iii)) in the temperature range of 253-313 K and a broad range of frequencies - from 4 kHz to 40 MHz. From the analysis of quadrupolar relaxation enhancement effects (quadrupolar peaks) associated with N nuclei, two lattice sites characterized by different electric field gradient tensors have been revealed. TheN quadrupolar couplings and asymmetry parameters at these sites differ by a factor of about two. Three motional processes have been identified and attributed to the overall dynamics of the NH(CH) cations (slow motion), dynamics of the NH groups (intermediate motion) and methyl group rotation (fast motion). It has been shown that the slow dynamics is only weakly temperature dependent, while the intermediate and fast motional processes are characterized by activation energies of 2.92 kJ mol and 0.41 kJ mol, respectively. The correlation time of the slow dynamics is of the order of μs, while the intermediate dynamics is faster by 2-3 orders of magnitude (depending on temperature). All correlation times have turned out to be independent of the position of the cations in the lattice (they are the same for both lattice sites). The analysis presented in this work is an example of the potential of the quadrupolar relaxation enhancement effects as a method revealing information on the dynamics and structure of solids.

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.…”

Model – free approach to quadrupole spin relaxation in solid 209Bi-aryl compounds

“…To some extent one can consider the Quadrupole Relaxation Enhancement (QRE) [12][13][14][15][16][17][18][19][20] as a counterpart of PRE. Yet the similarity concerns only the analogy in the Hamiltonian forms of ZFS and quadrupole interactions; the physical backgrounds of QRE and PRE are different.…”

1H spin–lattice relaxation in water solution of 209Bi counterparts of Gd3+contrast agents

“…In consequence, there are magnetic fields at which the 1 H Zeeman splitting (resonance frequency) matches one of the transition frequencies of the quadrupole nucleus between its energy levels. At such magnetic fields the 1 H polarisation can be taken over by the quadrupole nucleus that manifests itself as an enhancement of the 1 H spin-lattice relaxation (increasing of the relaxation rate), referred to as quadrupole peaks [20][21][22][23][24][25][26][27][28][29][30][31].…”