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A second polymorph of sodium di-hydrogen citrate, NaH2C6H5O7: structure solution from powder diffraction data and DFT comparison.

ABSTRACT: The crystal structure of a second polymorph of sodium di-hydrogen citrate, Na(+)·H2C6H5O7 (-), has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The powder pattern of the commercial sample used in this study did not match that corresponding to the known crystal structure [Glusker et al. (1965). Acta Cryst. 19, 561-572; refcode NAHCIT]. In this polymorph, the [NaO7] coordination polyhedra form edge-sharing chains propagating along the a axis, while in NAHCIT the octa-hedral [NaO6] groups form edge-sharing pairs bridged by two hy-droxy groups. The most notable difference is that in this polymorph one of the terminal carboxyl groups is deprotonated, while in NAHCIT the central carboxyl-ate group is deprotonated, as is more typical.

SUBMITTER: Rammohan A

PROVIDER: S-EPMC4908552 | biostudies-literature | 2016 Jun

REPOSITORIES: biostudies-literature

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A second polymorph of sodium di-hydrogen citrate, NaH2C6H5O7: structure solution from powder diffraction data and DFT comparison.

Rammohan Alagappa A Kaduk James A JA

Acta crystallographica. Section E, Crystallographic communications 20160527 Pt 6

The crystal structure of a second polymorph of sodium di-hydrogen citrate, Na(+)·H2C6H5O7 (-), has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The powder pattern of the commercial sample used in this study did not match that corresponding to the known crystal structure [Glusker et al. (1965). Acta Cryst. 19, 561-572; refcode NAHCIT]. In this polymorph, the [NaO7] coordination polyhedra form edge-sharing chains propaga ...[more]

PMID: 27308058

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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

A second polymorph of sodium di-hydrogen citrate, NaH2C6H5O7: structure solution from powder diffraction data and DFT comparison.

Publications

A second polymorph of sodium di-hydrogen citrate, NaH2C6H5O7: structure solution from powder diffraction data and DFT comparison.

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