The crystal structure of monoclinic γ-sulphur

Watanabe, Y.

doi:10.1107/s0567740874004961

Cited by 60 publications

(23 citation statements)

References 7 publications

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“…Nevertheless, in ref. 6 the X-ray measurement determines a structure with volume per molecule higher than that of α-S 8 , implying a 2.3% lower density. It could be possible that the temperature of the of the X-ray measurement was higher than 300K.…”

Section: A) β-S 8 Crystalsmentioning

confidence: 99%

“…The axis perpendicular to the molecular plane librates around its equilibrium orientation(z axis in Fig.3 γ-S 8 crystals can be grown from solutions 1,2 . The crystal is monoclinic, space group C 4 2h (P2/c), with four molecules per unit cell 6 . This pseudo-hexagonal structure is denser than that of α-S 8 , at the same temperature 2,6 .…”

Section: A) β-S 8 Crystalsmentioning

confidence: 99%

“…The crystal is monoclinic, space group C 4 2h (P2/c), with four molecules per unit cell 6 . This pseudo-hexagonal structure is denser than that of α-S 8 , at the same temperature 2,6 . Our simulations reproduce this structure (Fig.…”

Section: A) β-S 8 Crystalsmentioning

confidence: 99%

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Test of a simple and flexible molecule model for α-, β-, and γ-S8 crystals

Pastorino

Gamba

2000

The Journal of Chemical Physics

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Libertador 8250, (1429) Buenos Aires, Argentina. e-mails: clopasto@cnea.gov.ar and gamba@cnea.gov.ar S 8 is the most stable compound of elemental sulfur in solid and liquid phases, at ambient pressure and below 400K. Three crystalline phases of S 8 have been clearly identified in this range of thermodynamic parameters, although no calculation of its phase diagram has been performed yet. α-and γ-S 8 are orientationally ordered crystals while β-S 8 is measured as orientationally disordered. In this paper we analyze the phase diagram of S 8 crystals, as given by a simple and flexible molecule model, via a series of molecular dynamics (MD) simulations. The calculations are performed in the constant pressure-constant temperature ensemble, using an algorithm that is able to reproduce structural phase transitions. Introduction:Elemental sulfur shows a rich variety of molecular forms and therefore of chemical and physical properties in the crystalline and liquid phases 1,2 . Recently, a high pressure superconductor transition has been found, with T c =17K (at 162GPa), the highest known for any elemental solid 3 . Natural sulfur is of relevance in geophysics, astrophysics, material sciences and also of massive industrial use 1 . Nevertheless, the complex phase diagram and properties of its condensed phases are far from well known 1,2 .The most stable sulfur allotrope at ambient temperature and pressure (STP) is S 8 , a crown-shaped cyclic S 8 molecule, stable in solid, liquid and gas phases. 1Orthorhombic α-S 8 is the crystalline form stable at STP. Figs 1a shows its "crankshaft" structure with four molecules in the primitive unit cell. The space group is D 24 2h (Fddd), with 16 molecules in this non-primitive orthorhombic cell. If α-S 8 is slowly heated, it shows a phase transition to monoclinic β-S 8 at 369K (Fig. 1b), which melts at 393K 1 . Nevertheless, most α-S 8 crystals do no easily convert to β-S 8 , they melt, instead, at 385.8K 1,2 . β-S 8 is a monoclinic crystal, with six molecules in the primitive unit cell, two of them orientationally disordered 4,5 . A third crystalline allotrope has been observed: γ-S 8 (Fig. 1c), that can be obtained from solutions of S 8 or from its melt 1,2 . The space group is C 4 2h (P2/c), with four molecules in the pseudo-hexagonal closed-packed unit cell 6 . The density of this allotrope, at STP, is 5.8 % higher than that of α-S 8 .In spite of its relevance, calculations on the crystalline phase diagram of elemental sulfur molecules are scarce. Previous molecular dynamics (MD) simulations of crystalline S 8 were limited to constant-volume simulations at normal pressure and temperatures of α-S 8 7 , with the only aim to study the intramolecular frequencies obtained by Raman and ir. measurements. The same scope was followed by numerous works that measured crystalline frequencies and performed calculations based on lattice dynamics sums in different aproximations 8 .No attempt to reproduce the phase diagram of this molecule, including determination of crystalline structures, lat...

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Section: A) β-S 8 Crystalsmentioning

confidence: 99%

Section: A) β-S 8 Crystalsmentioning

confidence: 99%

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Test of a simple and flexible molecule model for α-, β-, and γ-S8 crystals

Pastorino

Gamba

2000

The Journal of Chemical Physics

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“…10, the uncertainty in our comparison with the scarce experimental data on β-and γ-S 8 phases is mainly due to contradictory measurements of γ-S 8 crystals. Density measurements at 300K imply that their density is 5.8% higher than that of α-S 8 at STP [2,7]. On the other hand the X-ray measurements [7] determine a crystalline cell with a larger volume per molecule than that of α-S 8 , implying a 2.3% lower density.…”

Section: Resultsmentioning

confidence: 94%

“…Density measurements at 300K imply that their density is 5.8% higher than that of α-S 8 at STP [2,7]. On the other hand the X-ray measurements [7] determine a crystalline cell with a larger volume per molecule than that of α-S 8 , implying a 2.3% lower density. Further measurements of this phase are needed.…”

Section: Resultsmentioning

confidence: 94%

Toward an anisotropic atom–atom model for the crystalline phases of the molecular S8 compound

Pastorino

Gamba

2001

The Journal of Chemical Physics

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We analize two anisotropic atom-atom models used to describe the crystalline α, β and γ phases of S 8 crystals, the most stable compound of elemental sulfur in solid phases, at ambient pressure and T < ∼ 400 K. The calculations are performed via a series of classical molecular dynamics (MD) simulations, with flexible molecular models and using a constant pressure-constant temperature algorithm for the numerical simulations. All intramolecular modes that mix with lattice modes, and are therefore relevant on the onset of structural phase transitions, are taken into account.Comparisons with experimental data and previous results obtained with an isotropic atom-atom molecular model are also performed.

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Transannular interactions in S82+ and Se82+: Reality or artifact?

Ciosłowski

Gao

1997

Int. J. Quant. Chem.

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Electronic structure calculations, carried out at the HFr6-311GU , MP2r6-311G U , and BLYPr6-311G U levels of theory, reveal an unexpectedly large influence of electron correlation on bonding in the octasulfur dication S are almost certainly distorted to a large degree by the crystal packing and counterion effects. The results of the present study underscore the need for a concerted experimental and theoretical effort to provide the definitive answer to the question of transannular interactions in chalcogen compounds.

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The crystal structure of monoclinic γ-sulphur

Cited by 60 publications

References 7 publications

Test of a simple and flexible molecule model for α-, β-, and γ-S8 crystals

Test of a simple and flexible molecule model for α-, β-, and γ-S8 crystals

Toward an anisotropic atom–atom model for the crystalline phases of the molecular S8 compound

Transannular interactions in S82+ and Se82+: Reality or artifact?

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