The crystal structure of oseltamivir phosphate has been refined using synchrotron X-ray powder diffraction data and optimized using density functional techniques. Oseltamivir phosphate crystallizes in space group P21212 (#18) with a = 24.0079(3), b = 24.6716(2), c = 7.45254(5) Å, V = 4414.24(5) Å3 at 295 K, and Z = 8. Prominent in the crystal structure are hydrogen bonds between the phosphate groups and the ammonium groups of the oseltamivir cations. The strong hydrogen bonds link the cations and the anions into columns parallel to the c-axis, with van der Waals interactions between the columns. Thermal expansion between 120 and 295 K is anisotropic. The powder pattern is included in the Powder Diffraction File™ as entry 00-068-1107.
