1H‐NMR Investigation of Methyl Group Reorientation and Cation Tumbling in Polycrystalline [X(CH3)4]I (X=N, P, As, Sb)

Rager, H.; Weiß, Alarich

doi:10.1002/bbpc.19760800209

Cited by 17 publications

(7 citation statements)

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“…[2,11] the relaxation rate IfT I is given by the equation may deduce that this interaction increases with increasing cation size. [2,11] the relaxation rate IfT I is given by the equation may deduce that this interaction increases with increasing cation size.…”

Section: Analysis Of Relaxation Time Data and Discussionmentioning

confidence: 99%

“…As already shown [2], the reorientation frequency of the cations [X{CH 3)4] + in [X{CH 3)4]I, X = N, P, As, Sb, can be calculated satisfactorily by Equations [12,13] …”

Section: Raman Measurementsmentioning

confidence: 91%

“…Der EinfluB des Anions auf die Spin-Gitter-Relaxation ist gering und besteht hauptsachlich in einer geringfiigigen Erhohung [1,2]. Bei tiefen Temperaturen sind die Protonen und die Fluorkerne durch Dipol-Dipol-Wechselwirkungen gekoppelt und beide Spinsysteme relaxieren hauptsachlich durch die Bewegungen der Methylgruppen.…”

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¹H and ¹⁹F Nuclear Spin‐Lattice Relaxation in Solid [X(CH₃)₄]₂SiF₆, X = N, P, As and Sb

Rager

Weiß

1978

Ber Bunsenges Phys Chem

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535Festkiirper / Magnetische Kernresonanz / Phasenumwandlungen / Ramanspektren / Rotation The~pin-Iattice relaxation times T 1 (1 H) and Ttl [9F) in the solid compounds [X(CH3)4]2SiF6' X = N, P, As, and Sb, were studied in the temperature range 125 K~T~460 K at a NMR frequency of 34 MHz. In the low temperature region protons and fluorine nuclei are coupled by dipole-dipole interactions and both spin systems relax mainly through the motions of the methyl groups. The activation energy of the methyl group reorientation, v", decreases with increasing size of the cation. With increasing temperature both T 1 ([ H) and T 1 ( 19 F) are influenced by the reorientation of the cations as a whole. The activation energy v,,1 of the reorientation of [X(CH 3)4] + was determined. From the linewidths of the free induction decays it is concluded that the dynamical behavior of the compounds is mainly determined by the size of the cations. The influence of the anion on T 1 is small causing a slight increase of the activation energy Va compared to v" in [X(CH 3)4]I. From the Raman spectrum of [N(CH3)4]2SiF6 a 90°reorientation mechanism of the cation seems most probable.Die Spin-Gitter-Relaxationszeiten der Protonen und Fluorkerne in den Verbindungen [X(CH3)4]2SiF6' X = N, P, As, Sb, wurden im Bereich 125 K~T~460 K bei 34 MHz studiert. Bei tiefen Temperaturen sind die Protonen und die Fluorkerne durch Dipol-Dipol-Wechselwirkungen gekoppelt und beide Spinsysteme relaxieren hauptsachlich durch die Bewegungen der Methylgruppen. Die Aktivierungsenergie der Methylgruppen-Reorientierung nimmt mit grolser werdendem Kation abo Mit steigender Temperatur bestimmt die Reorientierung des Kations zusatzlich die Spin-Gitter-Relaxation sowohl des Protonen-als auch des Fluorspinsystems. Die Aktivierungsenergie fiir die Reorientierung der Kationen wurde bestimmt. Sie ist nicht eindeutig von der Grofse und Art des Kations abhangig, Messungen der Linienbreite des freien Induktionsabfalles als Funktion der Temperatur bestatigen, daB die dynamischen Vorgange in diesen Verbindungen in erster Linie mit der GroBe des Kations gekoppelt sind. Der EinfluB des Anions auf die Spin-Gitter-Relaxation ist gering und besteht hauptsachlich in einer geringfiigigen Erhohung der Aktivierungsenergie der Methylgruppen-Reorientierung im Vergleich zu den entsprechenden Ergebnissen in den Verbindungen [X(CH 3)4]I. Die Raman-Spektren zeigen ebenfalls eine starke Anhangigkeit von der Art des Kations. Fiir [N(CH 3)4LSiF 6 ist aufgrund des Raman-Spektrums eine 90 0 -R e o r i e n t i e r u n g des Kations wahrscheinlich. Results a 90°t -90°pulse sequence with a Bruker BKR 322 s pulse spectrometer. Temperatures in the range 125 K s T~490 K have been reached at the site of the probes by means of a gas flow cryostat. The temperature was measured at the sample site with an accuracy of ± 1 K with the aid of a thermo couple. Furthermore, the free induction decay (FID) was studied. Additionally, Raman measurements were performed at room temperature with a Coderg Laser Raman spectromete...

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Section: Analysis Of Relaxation Time Data and Discussionmentioning

confidence: 99%

“…As already shown [2], the reorientation frequency of the cations [X{CH 3)4] + in [X{CH 3)4]I, X = N, P, As, Sb, can be calculated satisfactorily by Equations [12,13] …”

Section: Raman Measurementsmentioning

confidence: 91%

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¹H and ¹⁹F Nuclear Spin‐Lattice Relaxation in Solid [X(CH₃)₄]₂SiF₆, X = N, P, As and Sb

Rager

Weiß

1978

Ber Bunsenges Phys Chem

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“…As, where the temperature of maximum relaxation rate could be observed experimentally at a Larmor frequency of 34 MHz (360 K, 388 K, and 400 K for MV = N, P, and As, respectively) [15].…”

Section: Fmax Of [Sb(ch3)4] I Fits To the Corresponding Values Of Thementioning

confidence: 93%

Rotational Excitations and Tunneling of Nonequivalent Methyl Groups in Tetramethylstibonium Iodide as Studied by Nuclear Magnetic Resonance and Inelastic Neutron Scattering

Burbach

Weiß

1991

Zeitschrift Für Naturforschung A

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Nuclear magnetic resonance (NMR) and inelastic neutron scattering techniques (INS) have been applied to study the rotational motions and methyl group tunneling in tetramethylstibonium iodide, [Sb(CH3)4]I, over a wide temperature range. Parameters describing the [Sb(CH3)4]® cation tum bling and the methyl group reorientation at high temperatures and quantum mechanical tunneling of the methyl groups at low temperatures were determined.The results for INS and NMR experiments at low temperatures can be explained in terms of two crystallographically inequivalent methyl groups CH3(1) and CH3(2), which were established earlier by the crystal structure determination. In the INS spectra two tunneling lines at 22.0 peV for CH3(1) and 1.05 peV for CH3(2) with inelastic intensities in the ratio 3:1 were observed at 7 = 4 K.The activation energies derived from proton NMR spin-lattice relaxation time measurements for the thermally activated methyl group rotation are 1.50 kJ/mol for CH3(1) and 3.81 kJ/mol for CH3(2). They are in accordance with the activation energies obtained from neutron fixed-window measurements.The activation energy for [Sb(CH3)4]® cation tumbling is 50.9 kJ/mol as determined from the high temperature spin-lattice relaxation behaviour.Rotational potentials for the methyl groups are derived. For both kinds of inequivalent methyl groups the threefold potential terms dominate; three-and sixfold potential contributions are shifted by 180°. IntroductionRotational excitations of a methyl group provide a simple example of motional processes in the solid state. They have been studied both at higher tempera tures as thermally activated random reorientation and in the quantum mechanical regime at low temperatures. At very low temperatures the methyl group rotation can be described via quantum mechanical tunneling between the splitted torsional state [1], Increasing the temperature, rotation of the methyl group becomes thermally activated and can be treated classically. In the high temperature limit, additionally tumbling of the whole molecular framework can be activated in case of highly symmetric quasi spherical molecules or ions. Using nuclear magnetic resonance (NMR) meth ods, the activation energies of the thermally activated processes of the methyl group and the molecule as a whole as well as the reorientation rates can be deter mined [2].High resolution inelastic neutron spectroscopy (INS) has provided as suitable tool to determine the tunneling splitting in the quantum mechanical regime. The deter mination of this splitting is a good probe of the height and shape of the hindering potential barriers [3].Investigations of tetramethyl metal compounds with an element of the main group IV of the periodic system as central atom (e.g. tetramethyl lead, tetra methyl tin) have demonstrated that the interpretation of the NMR and INS data can not be described quan titatively without taking into account crystal structure data [4,5].The present investigation was undertaken to study the rotational behaviour of charged X(CH...

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“…Die n-Elektronenenergie ist danach am kleinsten bei der ebenen Molekulkonformation, wahrend die Wannenform mit axial stehenden n-Elektronenpaaren an den N-Atomen um -0,8719 p ungiinstiger ist. Setzt man fur p den ,,thermodynamischen" Wert von -85, 8 kJ/mol ein, der sich aus dem Vergleich der berechneten und experimentellen Delokalisierungsenergie von Benzol ergibt, so resultiert fur die angegebene Differenz dieser beiden Konformationen der Betrag 74.8 kJ/mol. Obwohl dieser Wert nur als grobe Abschatzung betrachtet werden darf, zeigt doch der Vergleich rnit den Aktivierungsenergien des cis-trans-Isomerisierungsprozesses, dal3 gleichzeitig rnit dem Einsetzen der cis-trans-Isomerisierung der Acylgruppen auch eine starkere Population der Wannenform gegeniiber der ebenen Molekulkonformation bei Erhohung der Temperatur eintreten konnte.…”

Section: Interpretation Der Meaergebnisseunclassified

DNMR‐kinetische Untersuchungen der Beweglichkeit von 1,4‐diacyl‐substituierten 1,4‐Dihydropyrazinen

Kollmannsberger

Gottlieb

Pfleiderer

1981

Ber Bunsenges Phys Chem

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The AA'BB'-part of the proton NMR spectra of the 1,4-diacyl-l,4-dihydropyrazines 1-4 reveals a strong temperature dependence resulting from the restricted rotation of both acyl groups around the C -N bonds. A dynamic model is postulated for the interconversion of the cis-and transforms which are in equilibrium. Activation enthalpies and activation entropies have been determined from the comparison of theoretical and experimental spectra. The results are discussed by use of HMO-calculations.

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¹H‐NMR Investigation of Methyl Group Reorientation and Cation Tumbling in Polycrystalline [X(CH₃)₄]I (X=N, P, As, Sb)

Cited by 17 publications

References 16 publications

¹H and ¹⁹F Nuclear Spin‐Lattice Relaxation in Solid [X(CH₃)₄]₂SiF₆, X = N, P, As and Sb

¹H and ¹⁹F Nuclear Spin‐Lattice Relaxation in Solid [X(CH₃)₄]₂SiF₆, X = N, P, As and Sb

Rotational Excitations and Tunneling of Nonequivalent Methyl Groups in Tetramethylstibonium Iodide as Studied by Nuclear Magnetic Resonance and Inelastic Neutron Scattering

DNMR‐kinetische Untersuchungen der Beweglichkeit von 1,4‐diacyl‐substituierten 1,4‐Dihydropyrazinen

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1H‐NMR Investigation of Methyl Group Reorientation and Cation Tumbling in Polycrystalline [X(CH3)4]I (X=N, P, As, Sb)

Cited by 17 publications

References 16 publications

1H and 19F Nuclear Spin‐Lattice Relaxation in Solid [X(CH3)4]2SiF6, X = N, P, As and Sb

1H and 19F Nuclear Spin‐Lattice Relaxation in Solid [X(CH3)4]2SiF6, X = N, P, As and Sb

Rotational Excitations and Tunneling of Nonequivalent Methyl Groups in Tetramethylstibonium Iodide as Studied by Nuclear Magnetic Resonance and Inelastic Neutron Scattering

DNMR‐kinetische Untersuchungen der Beweglichkeit von 1,4‐diacyl‐substituierten 1,4‐Dihydropyrazinen

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¹H‐NMR Investigation of Methyl Group Reorientation and Cation Tumbling in Polycrystalline [X(CH₃)₄]I (X=N, P, As, Sb)

¹H and ¹⁹F Nuclear Spin‐Lattice Relaxation in Solid [X(CH₃)₄]₂SiF₆, X = N, P, As and Sb

¹H and ¹⁹F Nuclear Spin‐Lattice Relaxation in Solid [X(CH₃)₄]₂SiF₆, X = N, P, As and Sb