6-Methyluracil: a redetermination of polymorph (II)

Gustavo Portalone
2019 IUCrData  
6-Mehyluracil, C5H6N2O2, exists in two crystalline phases: form (I), monoclinic, space group P21/c [Reck et al. (1988). Acta Cryst. A44, 417–421]. and form (II), monoclinic, space group C2/c [Leonidov et al. (1993). Russ. J. Phys. Chem. 67, 2220–2223]. The structure of polymorph (II) has been redetermined providing a significant increase in the precision of the derived geometric parameters. In the crystal, molecules form ribbons approximately running parallel to the c-axis direction through
more » ... rection through N—H...O hydrogen bonds. The radical differences observed between the crystal packing of the two polymorphs can be responsible in form (II) for an increase in the contribution of polar canonical forms C—(O−)=N—H+ relative to the neutral canonical form C(=O)—N—H induced by hydrogen-bonding interactions.
doi:10.1107/s2414314619008617 fatcat:zyny5pblw5bhpbwancr5z5pexe