Crystal structure of aqua(citric acid)(hydrogen citrato)calcium monohydrate, [Ca(HC6H5O7)(H3C6H5O7)(H2O)]·H2O, from synchrotron X-ray powder data, and DFT-optimized crystal structure of existing calcium hydrogen citrate trihydrate, [Ca(HC6H5O7)(H2O)3]

• Main Author: James A. Kaduk
• Format: Article
• Language: English
• Published: International Union of Crystallography 2020-10-01
• Series: Acta Crystallographica Section E: Crystallographic Communications
• Subjects: powder diffraction; citrate; calcium; rietveld refinement; density functional theory
• Online Access: http://scripts.iucr.org/cgi-bin/paper?S2056989020012864

The crystal structure of `aquabis(dihydrogen citrato)calcium hydrate', better formulated as aqua(citric acid)(hydrogen citrato)calcium monohydrate, (I), has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. The CaO8 coordination polyhedra are isolated, but occur in layers parallel to the ab plane. Both the Rietveld-refined and DFT-optimized structures indicate that one citrate is doubly ionized and that the other is citric acid. All of the active hydrogen atoms participate in strong (11–16 kcal mol−1) hydrogen bonds. Hydrogen atoms were added to the existing calcium hydrogen citrate trihydrate structure [Sheldrick (1974). Acta Cryst. B30, 2056–2057; CSD refcode: CAHCIT], (II), and a DFT calculation was carried out to assess the hydrogen bonding and compare it to this optimized structure.