The Far Infrared Spectra and X-Ray Powder Diffraction Patterns of the Structure I Hydrates of Cyclopropane and Ethylene Oxide at 100 °K

. Can. J. Chem. 62, 1229Chem. 62, (1984.NF3 is found to form a type I clathrate hydrate with a Pm3n cubic unit cell dimension of 1 1.91 A at 1 10 K and a dissociation pressure of 16.5 atm at 0°C. Dielectric studies below 100 K give, for reorientation of the NF3 dipole in the structure I cages, an average activation energy of 0.79 kcal mol-'. Well-resolved absorption peaks arising from NF3 incorporated in small and large cages of the structure I1 hydrate formed with SF6 give activation energies of 1.05 and 0.29 kcal m o l ' , respectively. '9 nmr lineshapes show in addition the presence of faster reorientation about the NF3 symmetry axis which is not completely removed even at 1.6 K. The pronounced effect of molecular oxygen impurity on the nmr linewidths at high magnetic fields and very low temperatures is-discussed. K sur la reorientation du dip6le NF, dans les cages de la structure I, donnent une Cnergie d'activation moyenne de 0,79 kcall mol. Les pics d'absorption bien rtsolus, provenant du NF, incorporC dans les petites et les grandes cages de la structure de I'hydrate I1 form6 avec le SF6, donnent respectivement des Cnergies d'activation de 1.05 et de 0,29 kcal/mol. La forme des pics en rmn du "F rCvkle de plus la prtsence d'une &orientation plus rapide autour de I'axe de symCtrie du NF3 qui n'est pas complktement CliminCe m&me B 1,6 K. On discute de I'effet prononct de I'impuretC de I'oxyg6ne molCculaire sur la largeur des pics en rmn B haut champ et 2 1 trks basse temptrature.[Traduit par le journal]That nitrogen trifluoride should form a clathrate hydrate is evident from its molecular size and chemical inertness toward water, as was pointed out long ago by von Stackelberg (I). No attempt to form NF, hydrate, however, has hitherto been recorded. We report here the identification of a structure 1 clathrate hydrate of NF, and the results of dielectric and I9F nmr I studies of reorientation of NF, molecules encaged in the structure I lattice as well as in structure I1 double hydrates formed with tetrahydrofuran, p-dioxane, and sulphur hexafluoride. Experimental methodsNF, hydrate samples were prepared by condensing NF3 (Air Products and Chemicals Inc.) at low temperatures into a pressure vessel containing degassed H 2 0 or D 2 0 ice and several stainless steel rods and allowing NF? and water to react at the temperatures and (final) pressures given in Table I . During the reaction period the pressure vessel was rolled so as to subject the solid sample to continuous grinding. Hydrate formation was monitored by the fall in gas pressure, which was normally complete in 24 h.Tetrahydrofuran (THF), p-dioxane (pD), and SF6 individually form hydrates of structure 11. Double hydrates of NF, with THF and p D were prepared by subjecting mixtures which contained 17 mol of D 2 0 per mole of structure I1 hydrate-former to the NF1 pressures shown in Table 1. The SF6-NF, double hydrate was formed from H 2 0 ice and a gas mixture containing about 44 mol% SF6. Again reaction was promoted by rolling and grinding The NF3 hydra...

Section: Unit Cell Parametermentioning

confidence: 79%

Characterization of a clathrate hydrate of nitrogen trifluoride

Davidson¹,

Garg²,

Ratcliffe³

et al. 1984

“…The X-ray samples consisted of the powdered hydrate in capillary tubes at 120 + 20 K, and a JarrellAsh precession camera was used as a flat-plate powder camera. Full details of the sample handling methods and the instrumentation and its calibration have been published (8)(9)(10)13 …”

Section: Methodsmentioning

confidence: 99%

“…The present study forms part of an examination of the vibrational spectra of the clathrate hydrates in this laboratory, to study the absorption by water molecules in different intermolecular configurations and the spectra of the clathrated guest molecules (8)(9)(10). Of particular interest in the present study are the presence of the three-coordinated water molecules, the partial orientational order of the water molecules and the possibility of long-range order at low temperature, and the loss of degeneracy and possible activation of vibrations in HMT by the reduction in site symmetry from the T, of pure HMT (ref.…”

Section: Introductionmentioning

confidence: 99%

The Infrared Spectrum Between 4000 and 200 cm⁻¹ and the X-Ray Powder Diffraction Pattern of Hexamethylenetetramine Hexahydrate in Four Isotopic Forms at 100 K

Bertie¹,

Solinas²

1975

Self Cite

The X-ray diffraction pattern of powdered hexamethylenetetramine hexahydrate (HMT-h12·6H2O ) at 120 K has been recorded and analyzed. The thermal contraction occurs primarily along the trigonal axis. The infrared spectra of polycrystallineHMT-h12·6H2O, HMT-h12·6D2O, HMT-d12·6H2O, and HMT-d12·6D2O at 95 K have been recorded. The most sensitive test for ice impurity is obtained from the OD stretching bands of HDO molecules in dilute solution in the hydrate, vOD(HDO), but ice impurity also affects the OH and OD stretching bands of H2O and D2O, vOH(H2O) and vOD(D2O). The absorption by HMT can be assigned to the single HMT molecule per diffraction unit cell. The symmetries of the vibrations under the C3v diffraction site symmetry cannot be determined from this data, so the absorption is assigned to the parent vibration of pure HMT.Three peaks arise from vOH(HDO) and vOD(HDO), at 2464 2369, and 2295 cm−1 for vOD(HDO). They can, with considerable uncertainty, be assigned to the three nonequivalent hydrogen bond lengths in the structure. An alternative assignment uses the hypothesis that the frequency of an O—D … O bond of given length is abnormally low when a three-coordinated oxygen atom is the base. A partial interpretation of the vOH(H2O) and vOD(D2O) bands is presented. It is quite clear that a large part of their breadth is due to Fermi resonance with the continuum of overtone and combination levels that lie close to the fundamental levels. Several fairly sharp features due to rotational vibrations of H2O and D2O, vR(H2O) and vR(D2O), provide the only evidence of the partial order in the positions of the hydrogen atoms. Three vR(HDO) frequencies have been detected, 860, 570, and 490 cm−1. Their ratios agree well with the ratios of the square roots of the reciprocal moments of inertia, but not with the ratios of frequencies calculated following Blue's arguments.

“…Such a result is to be expected in the light of the recent finding (13) that the C, , of the clathrate hydrates increases slightly with an increase in the unit cell size. Thc cubic cell parameter for structure I TMO hydrate is 12.02 A at 143 K (2) and for ethylene oxide hydrate is 1 1.89 P\ at 173 K (14). However, the C, values peratures outside the transition regions.…”

Section: Tmo Hydratesmentioning

confidence: 99%

A calorimetric study of trimethylene oxide and its structure I and structure II clathrate hydrates in the temperature range 85 to 270 K

Handa¹

1985

Y. P. HANDA. Can. J. Chem. 63, 68 (1985). Heat capacities and dissociation properties of trimethylene oxide and its structure 1 and structure I1 clathrate hydrates in the temperature range 85 to 270 K were determined using a Tian-Calvet heat flow calorimeter. The hydrates dissociate incongruently. The heat capacities of the hydrates are similar in magnitude to those observed for other structure I and structure 11 hydrates. For the structure I hydrate two thermal anomalies were observed. The one centered at 107 K can be identified as due to ordering of the trimethylene oxide dipoles along the 4 axes of the cages as suggested by the previous dielectric and nmr relaxation studies. The second centered at 168 K is interpreted as due to trimethylene oxide rich eutectic rather than due to some restructuring of the host lattice as has recently been suggested. Y. P. HANDA. Can. J. Chem. 63, 68 (1985) Utilisant un calorimktre a Ccoulement de chaleur du type Tian-Calvet et opCrant a des ternpkratures allant de 85 a 270 K, on a dtterminC les capacitCs calorifiques et les propriCtCs de dissociation de I'oxyde de trimethylene et de ses hydrates de clathrates de structures 1 et 11. Les modes de dissociation des hydrates ne sont pas congruents. Les capacitts calorifiques des hydrates sont du mCme ordre de grandeur que celles observes pour d'autres hydrates de structures I ou 11. On observe deux anomalies thermiques dans le cas de I'hydrate ayant la structure 1. L'une d'elle est centrke a 107 K et on peut l'attribuer au fait que les dipoles de I'oxyde de trimCthylkne se rkorientent le long des axes 5 de la cage, comme il a Ct C suggCrC par des Ctudes dielectriques et de relaxation en rmn qui ont Ct C effectuCes antkrieurement. Contrairement a ce qui a Ct C suggtrC rCcemment, on croit que la deuxikme anomalie, qui est centrCe a 168 K, serait due a un eutectique riche en oxyde de trimethylene plutBt qu'a une certaine restructuration du rCseau hBte.[Traduit par le journal]