Neutron Diffraction Determination of the Crystal Structure of Ammonium Bromide in Four Phases<sup>1</sup>

Levy, H. A.; Peterson, S. W.

doi:10.1021/ja01103a006

Cited by 192 publications

(71 citation statements)

References 14 publications

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“…The molecules form chains along the a direction at y = 0, z = 0 and y = ½, z = ½ with weak hydrogen bonds between N and Br of adjacent molecules (N...Br, 3.54 /k; cf. 3.47-3.51 /~ in NH4Br, Levy & Peterson, 1953). Contact between these chains in the c direction is primarily between the hydrocarbon ring on one molecule and Br atoms in molecules in the chain related by the e glide.…”

Section: Trans-d Ib R O M O B Is( C Y C Lo Hex Ylamine )P La Tinum (Ii)mentioning

confidence: 99%

trans-Dibromobis(cyclohexylamine)platinum(II)

Lock¹,

Zvagulis²

1980

Acta Crystallogr Sect B

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Introduction. The title compound was prepared by a modification of Dhara's (1970) method involving the reaction of K2[PtC14] (0.97 g) with KI (1.6 g) in water (10 ml). Cyclohexylamine (0.49 g) was added dropwise to the resulting solution and the yellow precipitate of [Pt(C6HIINH2)2I 2] was filtered off and dried. The yellow powder (0.66 g) was stirred with aqueous silver nitrate (0.34 g, 50 ml) for a week. AgI was removed by filtration and KBr solution (0.14 g, 25 ml)was added dropwise to the filtrate. A pale-yellow powder precipitated and was separated by filtration. This powder was dissolved in acetone and crystals of the title compound were obtained by slow evaporation of this solution. Composition: calculated, C, 26.1; H, 4.7; N, 5.1%; found, C, 26.3; H, 4.7; N, 5.0%. The crystals were long needles, the needle axis being a. A crystal, which was homogeneous under the polarizing microscope, was cut and ground into a cylinder of dimensions r = 0.07, l = 0.25 mm. Photographs showed the systematic absences of P21/c. The cell was determined by the least-squares fit of 15 well centred reflections (17 ° < 20 < 25 ° ) on a Syntex P21 diffractometer at 296 K and the density was determined by flotation in aqueous zinc bromide solutions, yielding Z = 2. The intensities of 1885 independent reflections up to 20 = 55 ° (hk + l) were measured with Mo Ka radiation at 296 K. The computer-controlled Syntex P21 diffractometer was operated in a 20(counter)-0(crystal) scan mode with a crystal monochromator. After removal of systematically absent reflections and of those for which I < ix(I), 1306 were considered observed [I > 3.0tr(I)] and were used for the structure determination; 191 were considered unobserved and were given no weight in the structure

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Section: Trans-d Ib R O M O B Is( C Y C Lo Hex Ylamine )P La Tinum (Ii)mentioning

confidence: 99%

trans-Dibromobis(cyclohexylamine)platinum(II)

Lock¹,

Zvagulis²

1980

Acta Crystallogr Sect B

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“…[P6yh6nen, Mansikka & Heiskanen (1964) have measured the lattice parameters between 297 and 467°K.] This modification undergoes a cooperative 2 transition at 234.5 °K to an ordered tetragonal structure which is closely related to the CsC1 structure (Levy & Peterson, 1953). At lower temperatures there is a sluggish first-order transition to an ordered CsCl-type structure.…”

mentioning

confidence: 90%

Low temperature X-ray investigation of NH₄Br

Bonilla¹,

Garland²,

Schumaker³

1970

Acta Cryst Sect A

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156SHORT COMMUNICATIONS present measurements. The ratio ux/ue however, was found to rise from 0.033 to 0.048 with the increased accelerating potential and so the beam homogeneity appears to be substantially independent of tube voltage.In Table 1 the observed flux changes at 30 kV are compared with those predicted on the basis of (1) for 30 kV and 12 kV for a beam of 1 mm diameter that subtends 16 minutes of arc (0.26 ° ) at the tube focus. The results show that for intensity measurements of 1% accuracy the take-off angle should never be less than about 5 ° for Cu Kct radiation.References ALEXANDER, L. E. • SMITH, G. S. (1962 The lattice parameters of NH4Br have been measured as a function of temperature from 5 to 150°K, a range which includes the region of the transition between cubic and tetragonal ordered phases. The lowtemperature CsCl-type phase exhibits normal thermal expansion up to ~ 108°K on warming, while the tetragonal diffraction pattern persists down to ~80°K on cooling. The present data are combined with previous measurements between 150 and 300°K to yield an overall picture of the variations associated with changes in ordering.Four different structural modifications of NH4Br are known to exist at low pressures, and a fifth modification of unknown structure has recently been observed above 2000 atm (Garland & Young, 1968). At one atmosphere and high temperatures NHaBr has a disordered NaCl-type structure, but it undergoes a first-order transition at 410°K to a disordered CsCl-type structure. [P6yh6nen, Mansikka & Heiskanen (1964) have measured the lattice parameters between 297 and 467°K.] This modification undergoes a cooperative 2 transition at 234.5 °K to an ordered tetragonal structure which is closely related to the CsC1 structure (Levy & Peterson, 1953). At lower temperatures there is a sluggish first-order transition to an ordered CsCl-type structure. Associated with this latter phase change is a marked hysteresis: the transition occurs at ~ 78 °K on cooling and at ~ 108 °K on warming (Stephenson & Adams, 1952;Sorai, Suga & Seki, 1965). The order-disorder referred to above involves the relative orientations of adjacent NH4 + ions. Below 234.5°K there is a long-range order in these orientations although this ordering will not be the same in the tetragonal and CsCl-type structure.Hovi, Heiskanen & Varteva (1965) have carried out a detailed X-ray determination of the lattice parameters of NHaBr as a function of temperature between 150 and 300 °K. The object of the present investigation was to confirm the cubic structure of the low-temperature phase, to determine the lattice parameter as a function of temperature, and to investigate by means of X-ray diffraction the region of the order-order transition at ~ 100 °K. To achieve these goals, we have obtained data between 5 and 150°K.

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“…Arbitrarily, ND4Br has been chosen as an example. In the early days of neutron diffraction, data on ND4Br were collected by Levy & Peterson (1953) and to date represent the only available data on all solid phases• These data will be reanalysed in the following, applying the method developed in paper I.…”

Section: Ammonium Bromidementioning

confidence: 99%

“…In phase I this coordination number reduces to six. Levy & Peterson (1953) have overcome the resultant difficulty by putting the deuterium atoms onto several equivalent (low-symmetry) positions or circles, both of which are occupied at random. Altogether eight different models have been tested, three of which satisfy the condition of a 'close approach between D and Br' (Levy & Peterson, 1953) and also give rather low R indices.…”

Section: (B) Nacl-type Structurementioning

confidence: 99%

“…In this simple case an explicit relation may be established between the wave function of the free molecule and the rotational formfactor Fr°t(R). Neutron data on phases I, II and IV of NDaBr (Levy & Peterson, 1953) are reanalysed in § IV: NDaBr has attracted much attention in the last few years. The phases under consideration are distinguished by particularly simple centre-of-mass structures with just one molecule per primitive cell.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Analysis of orientationally disordered structures. II. Examples: solid CD₄,p-D₂andMD₄Br

Press¹

1973

Acta Cryst Sect A

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In a number of examples a new method of analysing orientational structures of molecular crystals is illustrated. An application to solid heavy methane demonstrates a close analogy to magnetic structures. In the case of solid p-D2, structure factors are calculated on the basis of the rotational wave functions of the individual molecules and a comparison with neutron diffraction data is performed. Finally several solid phases of ND4Br, representative of the ammonium halides, are investigated and a better understanding of the orientational order in the NaCl-type phase is achieved.

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Neutron Diffraction Determination of the Crystal Structure of Ammonium Bromide in Four Phases¹

Cited by 192 publications

References 14 publications

trans-Dibromobis(cyclohexylamine)platinum(II)

trans-Dibromobis(cyclohexylamine)platinum(II)

Low temperature X-ray investigation of NH₄Br

Analysis of orientationally disordered structures. II. Examples: solid CD₄,p-D₂andMD₄Br

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Neutron Diffraction Determination of the Crystal Structure of Ammonium Bromide in Four Phases1

Cited by 192 publications

References 14 publications

trans-Dibromobis(cyclohexylamine)platinum(II)

trans-Dibromobis(cyclohexylamine)platinum(II)

Low temperature X-ray investigation of NH4Br

Analysis of orientationally disordered structures. II. Examples: solid CD4,p-D2andMD4Br

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Neutron Diffraction Determination of the Crystal Structure of Ammonium Bromide in Four Phases¹

Low temperature X-ray investigation of NH₄Br

Analysis of orientationally disordered structures. II. Examples: solid CD₄,p-D₂andMD₄Br