A new polymorph of 5-nitro-uracil monohydrate

Area of Science:

• Crystallography
• Chemical Physics
• Materials Science

Background:

• 5-nitrouracil is a derivative of uracil with potential biological and chemical applications.
• Understanding the solid-state structure of such compounds is crucial for predicting their properties and reactivity.
• Polymorphism in crystalline compounds can significantly influence their physical characteristics.

Purpose of the Study:

• To elucidate the crystal structure of 5-nitrouracil monohydrate.
• To characterize the hydrogen bonding network and molecular arrangement in the crystal lattice.
• To compare the structural features, specifically the nitro group orientation, with other known polymorphs of 5-nitrouracil.

Main Methods:

• Single-crystal X-ray diffraction was employed to determine the three-dimensional molecular structure.
• Analysis of intermolecular interactions, including hydrogen bonds, was performed.
• Geometric parameters, such as planarity of the pyrimidine ring and torsion angles, were calculated.

Main Results:

• The crystal structure of 5-nitrouracil monohydrate (C(4)H(3)N(3)O(4)·H(2)O) was successfully determined.
• Molecules of 5-nitrouracil form centrosymmetric hydrogen-bonded dimers.
• These dimers are further interconnected by water molecules into an extensive three-dimensional hydrogen-bonded network.
• The pyrimidine ring exhibits near planarity, with a nitro group rotation of 12.4(1)° relative to the ring plane.
• This rotation angle differs significantly from a previously reported polymorph (5°).

Conclusions:

• The crystal structure of 5-nitrouracil monohydrate reveals a complex hydrogen bonding network facilitating a 3D supramolecular architecture.
• The observed nitro group torsion angle provides a key structural differentiator between this hydrate form and other polymorphs.
• These findings contribute to the understanding of structure-property relationships in nitrouracil derivatives.