Abstract
The crystal structures of magnesium hydrogen citrate dihydrate, Mg(HC6H5O7)(H2O)2, (I), and bis-(di-hydrogen citrato)magnesium, Mg(H2C6H5O7)2, (II), have been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. In (I), the citrate anion occurs in the trans, trans-conformation, and triply chelates to the Mg cation. In (II), the citrate anion is trans, gauche, and doubly chelates to the Mg cation. In both compounds the Mg cation coordination polyhedron is an octa-hedron. In (I), the MgO6 coordination polyhedra are isolated, while in (II), they share edges to form chains. Strong O-H⋯O hydrogen bonds are prominent in the two structures, as well as in the previously reported magnesium citrate deca-hydrate.
Highlights
A systematic study of the crystal structures of Group 1 citrate salts has been reported in Rammohan & Kaduk (2018)
The citrate anion triply chelates to the Mg cation through the terminal carboxylate O14, the central carboxylate O15, and the hydroxyl group O17 oxygen atoms
The citrate triply chelates to a Mg through the hydroxyl group, the central carboxylate group, and one of the terminal carboxylate groups
Summary
A systematic study of the crystal structures of Group 1 (alkali metal) citrate salts has been reported in Rammohan & Kaduk (2018). (Fig. 1) The root-meansquare Cartesian displacement of the non-hydrogen citrate atoms in the Rietveld refined and DFT-optimized structures is 0.062 A (Fig. 2) The absolute difference in the position of the Mg cation in the unit cell is 0.055 A. The citrate anion triply chelates to the Mg cation through the terminal carboxylate O14, the central carboxylate O15, and the hydroxyl group O17 oxygen atoms. The crystal structure of (II) was solved and refined in the same way (Fig. 3) The root-mean-square Cartesian displacement of the non-hydrogen citrate atoms in the Rietveld. The root-mean-square Cartesian displacement of the nonhydrogen atoms in the reported and DFT-optimized structures of magnesium citrate decahydrate (MGCITD),. The citrate triply chelates to a Mg through the hydroxyl group, the central carboxylate group, and one of the terminal carboxylate groups
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