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The phase transition of rubidium hydrogen carbonate, RbHCO₃.

ABSTRACT: Rubidium hydrogen carbonate, RbHCO₃, features an order/disorder phase transition at T_C = 245?K from the high-temperature (HT) disordered C2/m modification to the low-temperature (LT) C-1 modification. The crystal structures are characterized by [HCO₃]₂^2- pairs of hydrogen carbonate groups connected by strong hydrogen bonding. The [HCO₃]₂^2- pairs are connected by Rb⁺ cations into a three-dimensional network. In HT-RbHCO₃, the hydrogen atom is disordered. In LT-RbHCO₃, ordering of the hydrogen atom leads to a translation-engleiche symmetry reduction of index 2. The lost reflections and rotations are retained as twin operations.

SUBMITTER: Larvor C

PROVIDER: S-EPMC5499272 | biostudies-literature | 2017 Jul

REPOSITORIES: biostudies-literature

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The phase transition of rubidium hydrogen carbonate, RbHCO3.

Larvor Carla C Stöger Berthold B

Acta crystallographica. Section E, Crystallographic communications 20170607 Pt 7

Rubidium hydrogen carbonate, RbHCO3, features an order/disorder phase transition at TC = 245 K from the high-temperature (HT) disordered C2/m modification to the low-temperature (LT) C-1 modification. The crystal structures are characterized by [HCO3]22- pairs of hydrogen carbonate groups connected by strong hydrogen bonding. The [HCO3]22- pairs are connected by Rb+ cati ...[more]

PMID: 28775864

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Project description:The crystal structure of sodium rubidium hydrogen citrate, NaRbHC6H5O7 or [NaRb(C6H6O7)] n , has been solved and refined using laboratory powder X-ray diffraction data, and optimized using density functional techniques. This compound is isostructural to NaKHC6H5O7. The Na atom is six-coordinate, with a bond-valence sum of 1.16. The Rb atom is eight-coordinate, with a bond-valence sum of 1.17. The distorted [NaO6] octa-hedra share edges to form chains along the a-axis direction. The irregular [RbO8] coordination polyhedra share edges with the [NaO6] octa-hedra on either side of the chain, and share corners with other Rb atoms, resulting in triple chains along the a-axis direction. The most prominent feature of the structure is the chain along [111] of very short, very strong hydrogen bonds; the O?O distances are 2.426 and 2.398?Å. The Mulliken overlap populations in these hydrogen bonds are 0.140 and 0.143 electrons, which correspond to hydrogen-bond energies of about 20.3?kcal?mol-1. The crystal structure of sodium caesium hydrogen citrate, NaCsHC6H5O7 or [NaCs(C6H6O7)] n , has also been solved and refined using laboratory powder X-ray diffraction data, and optimized using density functional techniques. The Na atom is six-coordinate, with a bond-valence sum of 1.15. The Cs atom is eight-coordinate, with a bond-valence sum of 0.97. The distorted trigonal-prismatic [NaO6] coordination polyhedra share edges to form zigzag chains along the b-axis direction. The irregular [CsO8] coordination polyhedra share edges with the [NaO6] polyhedra to form layers parallel to the (101) plane, unlike the isolated chains in NaKHC6H5O7 and NaRbHC6H5O7. A prominent feature of the structure is the chain along [100] of very short, very strong O-H?O hydrogen bonds; the refined O?O distances are 2.398 and 2.159?Å, and the optimized distances are 2.398 and 2.347?Å. The Mulliken overlap populations in these hydrogen bonds are 0.143 and 0.133 electrons, which correspond to hydrogen-bond energies about 20.3?kcal?mol-1.

Dataset Information

The phase transition of rubidium hydrogen carbonate, RbHCO₃.

Publications

The phase transition of rubidium hydrogen carbonate, RbHCO<sub>3</sub>.

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