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

The crystal structure of penta-sodium hydrogen dicitrate, Na5H(C6H5O7)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 octa-hedrally 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 NaO6 octahedra on both sides of these layers.