Nuclear Magnetic Resonance Experiment on Solid Hexamethyldisilane

Yukitoshi, Teruo; Suga, Hiroshi; Seki, Syûzô; Itoh, Junkichi

doi:10.1143/jpsj.12.506

Cited by 49 publications

(5 citation statements)

References 10 publications

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“…Considering the methyl group rotation, C in eq can be written as − C = N methyl N all 9 20 normalγ normalH 4 ℏ 2 r methyl 6 where N methyl and N all are the numbers of protons in the methyl group and the molecule, respectively, and r methyl is the average distance between the protons in the methyl group. From eqs and , the Δ M 2 values for 3-CH 3 and δ-CH 3 rotations are estimated to be 3.4 and 3.6 G 2 , respectively.…”

Section: Resultsmentioning

confidence: 99%

NMR Study of Cation Dynamics in Three Crystalline States of 1-Butyl-3-methylimidazolium Hexafluorophosphate Exhibiting Crystal Polymorphism

et al. 2012

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We investigate the cation rotational dynamics of a room temperature ionic liquid (RTIL) 1-butyl-3-methylimidazolium hexafluorophosphate ([C(4)mim]PF(6)) in its three crystalline states by (1)H NMR spectroscopy. Spin-lattice and spin-spin relaxation time (T(1) and T(2), respectively) measurements as a function of temperature confirm the presence of three polymorphic crystals of [C(4)mim]PF(6): crystals α, β, and γ, which we previously discovered using Raman spectroscopy and calorimetry. Second moment calculations of (1)H NMR spectra reveal that certain segmental motions of the butyl group in addition to the rapid rotation of the two methyl groups in the cation occur in all the crystals. The trend in the mobility of the segmental motions is γ < β ≤ α, which is consistent with the strength of cation-anion interactions (or crystal packing density) estimated from high-frequency Raman scattering experiments. T(1) measurements demonstrate two types of rotational motions on the nanosecond time scale in all three crystals: fast and slow motions. The three crystals have similar activation energies of 12.5-15.1 kJ mol(-1) for the fast motion, which is assigned to the rotation of the methyl group at the terminal of the butyl group. These observed activation energies were consistent with that estimated by quantum chemical calculations in the gas phase (11.9 kJ mol(-1)). In contrast, the slow motions of crystals α and γ are attributed to different segmental motions of the butyl group and that of crystal β to either a little segmental motion or a certain PF(6)(-) rotational motion. These nanosecond rotational motions obtained from the T(1) measurements do not appear to be affected by crystal packing density because local interactions in the crystalline state rather than packing density govern such nanosecond motions. With respect to the segmental motions, the mobility is likely to change significantly with the conformation of the butyl group. On the basis of these findings, crystal γ, which is the only crystalline phase previously determined using single-crystal X-ray diffraction, is considered to be the most stable phase because of the slowest segmental motions and the strongest cation-anion interactions.

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Section: Resultsmentioning

confidence: 99%

NMR Study of Cation Dynamics in Three Crystalline States of 1-Butyl-3-methylimidazolium Hexafluorophosphate Exhibiting Crystal Polymorphism

et al. 2012

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“…According to our theoretical results, the ⌬G 298 K values were 2 6 ‡ Ž . marginally greater than the ⌬E 0 K values in Si F and Si Me due to the 2 6 2 6 ‡ Ž .…”

mentioning

confidence: 84%

“…In Si H the ⌬E 0 K and ⌬G 298 K values were barrier at all. Recent reinvestigation of NMR experiments by Aksnes and Kimtys 10 cast doubts on the assignments of previous experiments 6 and found this barrier to be 1.64᎐1.69 kcalrmol. 10 Although this result is still slightly higher than ab initio values, the agreement between experiments and theories is much closer.…”

mentioning

confidence: 94%

Rotational barriers of disilane, hexafluorodisilane, and hexamethyldisilane: Ab initio, density functional, and molecular mechanics (MM3) studies

1997

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“…Since the Si-Si and Si-C bond distances are much longer than the corresponding distances in hydrocarbons, the steric effects should be considerably reduced, and typically the barriers are considerably smaller. The NMR study 75 was done in the crystal phase, and the high barrier is probably an artifact resulting from the lattice forces. Therefore, we believe the ab initio values should be more reliable.…”

Section: Polysilanesmentioning

confidence: 99%