Polymorphism in Br₂ Clathrate Hydrates

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Abstract

The structure and composition of bromine clathrate hydrate has been controversial for more than 170 years due to the large variation of its observed stoichiometries. Several different crystal structures were proposed before 1997 when Udachin et al. (Udachin, K. A.; Enright, G. D.; Ratcliffe, C. I.; Ripmeester, J. A. J. Am. Chem. Soc. 1997, 119, 11481) concluded that Br₂ forms only the tetragonal structure (TS-I). We show polymorphism in Br₂ clathrate hydrates by identifying two distinct crystal structures through optical microscopy and resonant Raman spectroscopy on single crystals. After growing TS-I crystals from a liquid bromine−water solution, upon dropping the temperature slightly below −7 °C, new crystals of cubic morphology form. The new crystals, which have a limited thermal stability range, are assigned to the CS-II structure. The two structures are clearly distinguished by the resonant Raman spectra of the enclathrated Br₂, which show long overtone progressions and allow the extraction of accurate vibrational parameters:  ω_e = 321.2 ± 0.1 cm^-1 and ω_ex_e = 0.82 ± 0.05 cm^-1 in TS-I and ω_e = 317.5 ± 0.1 cm^-1 and ω_ex_e = 0.70 ± 0.1 cm^-1 in CS-II. On the basis of structural analysis, the discovery of the CS-II crystals implies stability of a large class of bromine hydrate structures and, therefore, polymorphism.

Citing Articles

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This article has been cited by 4 ACS Journal articles (4 most recent appear below).

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  Large Shift and Small Broadening of Br₂ Valence Band upon Dimer Formation with H₂O: An Ab Initio Study

  Ricardo Franklin-Mergarejo , Jesus Rubayo-Soneira , Nadine Halberstadt , Tahra Ayed , Margarita I. Bernal-Uruchurtu and Ramón Hernández-Lamoneda , Kenneth C. Janda
  The Journal of Physical Chemistry A2011 115 (23), 5983-5991

  • Large Shift and Small Broadening of Br₂ Valence Band upon Dimer Formation with H₂O: An Ab Initio Study

    Ricardo Franklin-Mergarejo , Jesus Rubayo-Soneira , Nadine Halberstadt , Tahra Ayed , Margarita I. Bernal-Uruchurtu and Ramón Hernández-Lamoneda , Kenneth C. Janda
    The Journal of Physical Chemistry A2011 115 (23), 5983-5991

    Valence electronic excitation spectra are calculated for the H2O···Br2 complex using highly correlated ab initio potentials for both the ground and the valence electronic excited states and a 2-D approximation for vibrational motion. Due to the strong ...

    Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links
• 

  On the Structure Selectivity of Clathrate Hydrates

  Masakazu Matsumoto and Hideki Tanaka
  The Journal of Physical Chemistry B2011 Article ASAP

  • On the Structure Selectivity of Clathrate Hydrates

    Masakazu Matsumoto and Hideki Tanaka
    The Journal of Physical Chemistry B2011 Article ASAP

    We propose a strategic method to search for a new clathrate hydrate by investigating the selectivity of its crystalline structure, which has been expected to depend mostly on the guest species and less on the thermodynamic conditions. Relative stability ...

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• 

  Molecular Dynamics Simulations of Bromine Clathrate Hydrates

  Daniel P. Schofield and Kenneth D. Jordan
  The Journal of Physical Chemistry A2009 113 (26), 7431-7438

  • Molecular Dynamics Simulations of Bromine Clathrate Hydrates

    Daniel P. Schofield and Kenneth D. Jordan
    The Journal of Physical Chemistry A2009 113 (26), 7431-7438

    A polarizable force field that explicitly includes contributions from exchange repulsion, dispersion, charge penetration, and multipole electrostatics was developed to describe the interaction between bromine and water. This force field was combined with ...

    Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links
• 

  On the Unusual Properties of Halogen Bonds: A Detailed ab Initio Study of X₂−(H₂O)₁₋₅ clusters (X = Cl and Br)

  Margarita I. Bernal-Uruchurtu and Ramón Hernández-Lamoneda, Kenneth C. Janda
  The Journal of Physical Chemistry A2009 113 (19), 5496-5505

  • On the Unusual Properties of Halogen Bonds: A Detailed ab Initio Study of X₂−(H₂O)₁₋₅ clusters (X = Cl and Br)

    Margarita I. Bernal-Uruchurtu and Ramón Hernández-Lamoneda, Kenneth C. Janda
    The Journal of Physical Chemistry A2009 113 (19), 5496-5505

    Halogen bonds have received a great deal of attention in recent years. Their properties, sometimes paralleled with those of hydrogen bonds, have not yet been fully understood. In this work, we investigate the nature of the intermolecular interactions ...

    Abstract | Full Text HTML | Hi-Res PDF | PDF w/ Links

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