Sodium dipotassium citrate, NaK(2)C(6)H(5)O(7)

The crystal structure of sodium dipotassium citrate, Na(+)·2K(+)·C(6)H(5)O(7) (3−), has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The Na(+) and one of the K(+) cations are six-coordinate, with bond-valence sums of 1.13 and 0.92 valence units, respectively, while another crystallographically independent K(+) cation is seven-coordinate with a bond-valence sum of 1.20. The [KO(6)] and [KO(7)] polyhedra share edges and corners to form layers perpendicular to the b axis. The distorted [NaO(6)] octa­hedra share edges to form chains along the a axis. The result is a three-dimensional network. The only O—H⋯O hydrogen bond is an intra­molecular one between the hy­droxy group and a terminal carboxyl­ate group.