Sodium potassium hydrogen citrate, NaKHC6H5O7

The crystal structure of sodium potassium hydrogen citrate has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional theory techniques. The Na+ cation is six-coordinate, with a bond-valence sum of 1.17. The K+ cation is also six-coordinate, with a bondvalence sum of 1.08. The distorted [NaO6] octahedra share edges, forming chains along the a axis. The likewise distorted [KO6] octahedra share edges with the [NaO6] octahedra on either side of the chain, and share corners with other [KO6] octahedra, resulting in triple chains along the a axis. The most prominent feature of the structure is the chain along [111] of very short, very strong hydrogen bonds; the O center dot center dot center dot O distances are 2.414 and 2.400 angstrom. The Mulliken overlap populations in these hydrogen bonds are 0.138 and 0.142 e, which correspond to hydrogen-bond energies of 20.3 and 20.6 kcal mol(-1).