Abstract
The crystal structures of disodium hydrogen citrate monohydrate, Na2HC6H5O7(H2O), and di-ammonium sodium citrate, (NH4)2NaC6H5O7, have been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. In NaHC6H5O7(H2O), the NaO6 coordination polyhedra share edges, forming zigzag layers lying parallel to the bc plane. The hydro-phobic methyl-ene groups occupy the inter-layer spaces. The carb-oxy-lic acid group makes a strong charge-assisted hydrogen bond to the central carboxyl-ate group. The hydroxyl group makes an intra-molecular hydrogen bond to an ionized terminal carboxyl-ate oxygen atom. Each hydrogen atom of the water mol-ecule acts as a donor, to a terminal carboxyl-ate and the hydroxyl group. Both the Na substructure and the hydrogen bonding differ from those of the known phase Na2HC6H5O7(H2O)1.5. In (NH4)2NaC6H5O7, the NaO6 coordination octa-hedra share corners, making double zigzag chains propagating along the b-axis direction. Each hydrogen atom of the ammonium ions acts as a donor in a discrete N-H⋯O hydrogen bond. The hydroxyl group forms an intra-molecular O-H⋯O hydrogen bond to a terminal carboxyl-ate oxygen atom.
Highlights
The crystal structures of disodium hydrogen citrate monohydrate, Na2HC6H5O7(H2O), and diammonium sodium citrate, (NH4)2NaC6H5O7, have been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques
Each hydrogen atom of the ammonium ions acts as a donor in a discrete N—HÁ Á ÁO hydrogen bond
As part of our ongoing studies in this area, we report the syntheses and structures of disodium hydrogen citrate monohydrate, Na2HC6H5O7(H2O), (I), and diammonium sodium citrate, (NH4)2NaC6H5O7, (II)
Summary
A systematic study of the crystal structures of Group 1 (alkali metal) citrate salts has been reported in Rammohan & Kaduk (2018). The study was extended to ammonium citrates in Wheatley & Kaduk (2019). Na2HC6H5O7(H2O) was an accidental product of an extension of the program to mixed ammonium–group 1 citrates, and (NH4)2NaC6H5O7 was an intended product. Another product in the series is (NH4)2KC6H5O7 (Patel et al, 2020). As part of our ongoing studies in this area, we report the syntheses and structures of disodium hydrogen citrate monohydrate, Na2HC6H5O7(H2O), (I), and diammonium sodium citrate, (NH4)2NaC6H5O7, (II)
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