Molecular Motion in Solid [Sb(CH3)4]X, X = Cl, Br, I, PF6, and BF4. 1H, 19F NMR Second Moment and Crystal Structure

Burbach, G.; Dou, Shuo; Weiß, Alarich

doi:10.1002/bbpc.19890931132

Cited by 10 publications

(9 citation statements)

References 28 publications

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“…Using a mean value rc = 401 pm for the distance of the centers of the CH3 groups in [Sb(CH3)4]I [7] and the same value for r as in (5) At very low temperatures (Fig. 5) the methyl group rotation can be described as a quantum mechanical process.…”

Section: Resultsmentioning

confidence: 99%

“…The two peaks at | h cot°| = 22.0 peV and | ftcot°| = 1.05 peV with inelastic intensities in the ratio 3:1 are in accordance with the results of the crystal structure determination. The crys tal structure was determined by single crystal X-ray technique at room temperature [7], [Sb(CH3)4] I crys tallizes in the space group Cgv-P63mc with 2 formula units in the unit cell. Two crystallographically inequiv alent carbon atoms in the ratio C(1):C(2) = 3 :1 were found.…”

Section: Discussionmentioning

confidence: 99%

“…Tetramethylstibonium iodide (sublimation point: 528 K) was prepared as described previously [7], Neutron scattering investigations were carried out using the time-of-flight spectrometer IN 5 and the backscattering spectrometer IN 10 at the ILL, Grenoble.…”

Section: Methodsmentioning

confidence: 99%

“…Thus, rotational tunneling in the tetramethylstibo nium cation was expected [6], Tetramethylstibonium iodide, [Sb(CH3)4] I, was chosen, since the crystal struc ture at room temperature has recently been deter mined [7], 0932-0784 / 91 / 0900-0746 S 01.30/0. -Please order a reprint rather than making your own copy.…”

Section: Introductionmentioning

confidence: 99%

“…In the temperature range 77 < T/K < 256 rotation of the methyl groups about the threefold axes occurs [7].…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…In the temperature range 77 < T/K < 256 rotation of the methyl groups about the threefold axes occurs [7].…”

Section: Introductionmentioning

confidence: 99%