Sodium dirubidium citrate, NaRb2C6H5O7, and sodium dirubidium citrate dihydrate, NaRb2-C6H5O7(H2O)2

The crystal structures of sodium dirubidium citrate {poly[mu-citrato-dirubidium(I)sodium(I)], [NaRb2(C6H5O7)](n)} and sodium dirubidium citrate dihydrate {poly[diaqua(mu-citrato)dirubidium(I)sodium(I)], [NaRb2(C6H5O7)-(H2O)(2)](n)} have been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. Both structures contain Na chains and Rb layers, which link to form different three-dimensional frameworks. In each structure, the citrate triply chelates to the Na+ cation. Each citrate also chelates to Rb+ cations. In the dihydrate structure, the water molecules are bonded to the Rb+ cations; the Na+ cation is coordinated only to citrate O atoms. Both structures contain an intramolecular O-H center dot center dot center dot O hydrogen bond between the hydroxy group and one of the terminal carboxylate groups. In the structure of the dihydrate, each hydrogen atom of the water molecules participates in a hydrogen bond to an ionized carboxylate group.