Molecular motion in solid complexes of trimethylamine with boron trihalides and borane

Yim, C. T.; Gilson, D. F. R.

doi:10.1139/v70-086

Cited by 22 publications

(9 citation statements)

References 10 publications

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“…Although some discrepancy can be recognized between our calculated second moment values and those in ref. 9, our analysis of the experimental second moments led to the same assignment of the molecular motion as given in ref. 9: i.e., the large change in the second moments of both 'H and 19F below about 90 K is caused bv the simultaneous excitation of the reorientation or rotation of the methyl groups about the C-N bonds (C3 rotation) and the reorientation of the BF3 group about the N-B bond (CF rotation), and another change of the proton second moment between 100 and 150 K is brought about by the reorientation of the TMA group about the N-B bond (C; rotation) in addition to C3 and CF rotations.…”

Section: Second Momentsupporting

confidence: 67%

“…Previous measurements of the linewidths and the second moments of both 'H and ' 9~ down to 68 K did not reach the rigid-lattice values (9,10). We therefore extended the temperature region of the continuous-wave experiments down to 53 K. The results indicate that the second moment of 'H reaches an almost flat plateau below 60 K at (31 * 1) G2.…”

Section: Second Momentmentioning

confidence: 80%

“…D(TF,X) represents the same quantity as in eq. [9] except that A and 2wo are replaced by wF -wx and wF + wx, respectively. Using structural data, the intra-BF3 relaxation rate is calculated to be Finally, the relaxation rate (TYB)-I is ignored.…”

Section: Temperature Dependence Of Timentioning

confidence: 99%

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Molecular motion in the crystalline donor–acceptor complex trimethylamine–trifluoroborane as studied by proton and fluorine magnetic resonance

Chihara¹,

Nakamura²,

Chihara³

1988

Can. J. Chem.

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This paper is dedicated to Professor Charles A. McDowell on the occasion of his 70th birthday YUKIKO N. CHIHARA, NOBUO NAKAMURA, and HIDEAK~ CHIHARA. Can. J. Chem. 66, 1848 (1988). The proton and fluorine second moments and the spin-lattice relaxation times TI (at 25.75 MHz) were measured in the solid complex trimethylamine-trifluoroborane from 53 to 300 K. There is a cross-relaxation effect between 'H and 1 9~ below 120 K. Their TI minima near 140 K led to activation energies of 10.6 and 11.1 kJ mol-I for the reorientation of the methyl and the trifluoride groups, respectively. An additional minimum observed in the TI of protons at about 240 K was attributed to the reorientation of the trimethylamine group about the N-B bond with an activation energy of 25.0 kJ mol-I. A comparison of these potential parameters with those in other trimethylamine complexes led to a notion that the activation energies for the reorientation of the (CH3)3N group in the trimethylamine-trifluoroborane complex are mainly governed by the intramolecular steric effect. Trimethylamine (TMA) forms donor-acceptor complex compounds with a variety of electron accepting materials (1). Some of these complexes have threefold symmetry and different types of intramolecular degrees of freedom. Moreover, some undergo a phase transition or transitions in their crystalline state (2-4) but the nature of the phase transitions has not yet been clarified. To understand the mechanism of phase transition(s) as well as the intricate inter-or intramolecular interactions in the crystals of these molecular complexes, studies are necessary both of the dynamical properties of molecules and of the crystal lattices in relation to detailed structural studies.The 1:l complex compound between TMA and trifluoroborane (TFB) is a typical example of such a complex. It has a molecular threefold symmetry axis and three intramolecular rotational degrees of freedom, and can undergo two different rotations as a whole, i.e., the rotations about the molecular symmetry axis and about the two short axes. The molecule has a large dipole moment (5.76 D) (5) and the crystal belongs to a rhombohedra1 space group with three TMB .TFB complexes per unit cell (6). This compound does not undergo any phase transition between 77 K and its melting point and therefore is a good specimen for examining molecular motion in detail without interruption by the discontinuities of a phase transition. This paper presents the results of proton and fluorine nuclear magnetic resonance and relaxation measurements below room temperature. The molecular modes are assigned and the cross-relaxation effect between the proton and fluorine is discussed. The origin of the activation processes and the possible mechanism of phase transitions in trimethylamine complexes will be considered. ExperimentalTMA-TFB was synthesized according to a method reported in the literature (7); a saturated aqueous solution of KOH was added to trimethylamine hydrochloride from a commercial source and gaseous TMA thus generated was intro...

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Section: Second Momentsupporting

confidence: 67%

Section: Second Momentmentioning

confidence: 80%

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Molecular motion in the crystalline donor–acceptor complex trimethylamine–trifluoroborane as studied by proton and fluorine magnetic resonance

Chihara¹,

Nakamura²,

Chihara³

1988

Can. J. Chem.

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“…lattice second moment value can be obtained as The preexponential factors w 0 and wЉ 0 are given by [28] which is equivalent to Eq.…”

Section: Correlation Functionsmentioning

confidence: 99%

Dipolar NMR Spectrum of a Solid Narrowed by a Complex Molecular Motion

Latanowicz

Reynhardt

1996

Journal of Magnetic Resonance, Series A

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“…study of molecular motions in complexes of trimethylamine with boron trihalides and borane, line-width and secondmoment transitions were observed and attributed to methyl group reorientation in the temperature range below 110 O K , followed by rotation of the trimethylamine group about the B-N axis at higher temperatures (1). For the borane and boron trifluoride complexes it is probable that reorientation of these groups occurred prior to the onset of rotation of the trimethylamine group.…”

Section: Introductionmentioning

confidence: 97%

Temperature dependence of the ³⁵Cl nuclear quadrupole resonance in the trimethylamine – boron trichloride complex

Gilson¹,

Hart²

1970

Can. J. Chem.

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A 35C1 nuclear quadrupole resonance study of the trimethylamine -boron trichloride complex has revealed line-width and frequency changes which correlate with transitions observed in the wide-line proton magnetic resonance study.Canadian Journal of Chemistry, 48, 1976 (1970) IntroductionIn a recent wide-line nuclear magnetic resonance (n.m.r.) study of molecular motions in complexes of trimethylamine with boron trihalides and borane, line-width and secondmoment transitions were observed and attributed to methyl group reorientation in the temperature range below 110 O K , followed by rotation of the trimethylamine group about the B-N axis at higher temperatures (1). For the borane and boron trifluoride complexes it is probable that reorientation of these groups occurred prior to the onset of rotation of the trimethylamine group. It was not possible to determine from these studies whether or not motion of the BCI, or BBr, groups occurred, although the activation energies determined from line-width analyses were about 9 kcal mole-' for trimethylamine rotation compared with about 2 kcal mole-' for the same process in the BF, and BH, complexes. This suggested that the molecule rotates as a whole rather than uncorrelated motion of the two halves.We have examined the frequency and "apparent" line widths of the 35C1 nuclear quadrupole resonance as a fuilction of temperature in the trimethylamine -boron trichloride complex to obtain additional information on the molecular motion in these compounds.The nuclear quadrupole resonance (n.q.r.) frequencies of a series of boron trichloride complexes were first reported by Kaplansky and Whitehead (2). For the trimethylamine complex at 77 OK, two lines were observed, at 21.765 and 21.340 MHz, with an intensity ratio of 2:l.

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Molecular motion in solid complexes of trimethylamine with boron trihalides and borane

Abstract: Wide line nuclear magnetic resonance studies of trimethylamine complexes of BF,, BCI,, BBr,, and BH, show that rotation of methyl groups and rotation about the B-N axes occur in the solid phases. The complex between ammonia and boron trifluoride has also been studied.

Cited by 22 publications

References 10 publications

Molecular motion in the crystalline donor–acceptor complex trimethylamine–trifluoroborane as studied by proton and fluorine magnetic resonance

Molecular motion in the crystalline donor–acceptor complex trimethylamine–trifluoroborane as studied by proton and fluorine magnetic resonance

Dipolar NMR Spectrum of a Solid Narrowed by a Complex Molecular Motion

Temperature dependence of the ³⁵Cl nuclear quadrupole resonance in the trimethylamine – boron trichloride complex

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Molecular motion in solid complexes of trimethylamine with boron trihalides and borane

Abstract: Wide line nuclear magnetic resonance studies of trimethylamine complexes of BF,, BCI,, BBr,, and BH, show that rotation of methyl groups and rotation about the B-N axes occur in the solid phases. The complex between ammonia and boron trifluoride has also been studied.

Cited by 22 publications

References 10 publications

Molecular motion in the crystalline donor–acceptor complex trimethylamine–trifluoroborane as studied by proton and fluorine magnetic resonance

Molecular motion in the crystalline donor–acceptor complex trimethylamine–trifluoroborane as studied by proton and fluorine magnetic resonance

Dipolar NMR Spectrum of a Solid Narrowed by a Complex Molecular Motion

Temperature dependence of the 35Cl nuclear quadrupole resonance in the trimethylamine – boron trichloride complex

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Temperature dependence of the ³⁵Cl nuclear quadrupole resonance in the trimethylamine – boron trichloride complex