Crystal structure of penta­sodium hydrogen dicitrate from synchrotron X-ray powder diffraction data and DFT comparison

The crystal structure of penta­sodium hydrogen dicitrate, Na(5)H(C(6)H(5)O(7))(2), has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. Each of the two independent citrate anions is joined into a dimer by very strong centrosymmetric O—H⋯O hydrogen bonds, with O⋯O distances of 2.419 and 2.409 Å. Four octa­hedrally coordinated Na(+) ions share edges to form open layers parallel to the ab plane. A fifth Na(+) ion in trigonal–bipyramidal coordination shares faces with NaO(6) octahedra on both sides of these layers.