Omadacycline dihydrate, C 29 H 40 N 4 O 7 ·2H 2 O, from X-ray powder diffraction data.

The crystal structure of the title compound {systematic name: (4 S ,4a S ,5a R ,12a R )-4,7-bis-(di-methyl-amino)-9-[(2,2-di-methyl-propyl-amino)-meth-yl]-1,10,11,12a-tetra-hydroxy-3,12-dioxo-4a,5,5a,6-tetra-hydro-4 H -tetra-cene-2-carb-oxamide dihydrate, C 29 H 40 N 4 O 7 ·2H 2 O} has been solved and refined using synchrotron X-ray powder diffraction data: it crystallizes in space group R 3 with a = 24.34430 (7), c = 14.55212 (4) Å, V = 7468.81 (2) Å 3 and Z = 9. Most of the hydrogen bonds are intra-molecular, but two classical N-H⋯O inter-molecular hydrogen bonds (along with probable weak C-H⋯O and C-H⋯N hydrogen bonds) link the mol-ecules into a three-dimensional framework. The framework contains voids, which contain disordered water mol-ecules. Keto-enol tautomerism is apparently important in this mol-ecule, and the exact mol-ecular structure is ambiguous.