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

Abstract

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.

Structural studies of coordination compounds. A joint NQR and x-ray investigation of trialkylphosphine-gallium trichloride adducts

“…Equation 4 may be derived by substitution of this expression into the normal Bayer equation, whence for a single vibrational mode p = 3/ /8 2 (0) (6) and q=hco(0)/k (7…”

“…4 No crystal structure of a gallium analogue has been reported although gas-phase electron diffraction measurements on related compounds are known.5 Broad-line NMR and NQR variable temperature data for trimethylamine boron trichloride have been explained by Gilson and Hart in terms of hindered molecular rotation. 6 Apparently this is in conflict with the published x-ray structure,2 in which the atomic positions are well defined; however, the difficulty may possibly be resolved if the difference in time scale of the experiments is considered and a suitable rotational transition rate postulated.…”

“…510 (9)] A #3= 113.84 (7)°[113.86 (9)°] V= 467.6 (1.2) [475.4 (1.5)] A3 Pexptl = 1-75 (2)g/cm3 Px = 1.76 g/cm3Absorption factor: P(\mo) = 40 cm-1 Morphology: parallelepiped; 0.019 X 0.041 X 0.006 cm Min and max absorption corrections: 0.23, 0.632. Data Collection Temperature: 223 K [297 K] Radiation: molybdenum ( ) 0.71069 A Monochromatization: oriented graphite crystal Crystal-detector distance: 208 mm Detector window: height6 = 4 mm, width6 = 3.10 + 0.70 tan 0 Takeoff angle:6 3.5°S can mode: , Max Bragg angle: ¿ = 30°S can angle: = 0 + B tan 6, 606 = 1.30, Bb = 0.35 Values determining the scan speed: SIGPRE6 = 0.400, SIGMA6 = 0.020, VPRE6 = 5°/min, TMAX6 = 90 s ControlConditions for Refinement Reflections for the refinement of the cell dimensions: 25 Recorded reflections: 1522 [1558] Independent reflections: 1423 [1457] Utilized reflections: 924 [732] with / > 3 (/) Refined parameters: 57 [43] Reliability factors: R = Z\k\F0\ -\Fc\\¡Zk\F0\= 0.038 [0.063] (mthw = 4F02io1(F02)),RV!=[Zw{k\F0\-\Fi.\)2li;wk2F02Y'1 0.047 [0.068] 0 Data are given for the structure at 223 K; values obtained at 297K are enclosed in brackets 6. Cf.…”