The crystal structure of a second polymorph of sodium di-hydrogen citrate, Na(+)·H2C6H5O7 (-), has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The powder pattern of the commercial sample used in this study did not match that corresponding to the known crystal structure [Glusker et al. (1965). Acta Cryst. 19, 561-572; refcode NAHCIT]. In this polymorph, the [NaO7] coordination polyhedra form edge-sharing chains propagating along the a axis, while in NAHCIT the octa-hedral [NaO6] groups form edge-sharing pairs bridged by two hy-droxy groups. The most notable difference is that in this polymorph one of the terminal carboxyl groups is deprotonated, while in NAHCIT the central carboxyl-ate group is deprotonated, as is more typical.
Keywords: citrate; crystal structure; density functional theory; polymorphs; powder diffraction; sodium.