Alloying barbituric and thiobarbituric acids: from solid solutions to a highly stable keto co-crystal form

Area of Science:

• Solid-state chemistry
• Crystallography
• Materials science

Background:

• Barbituric acid (BA) and thiobarbituric acid (TBA) are isomorphous compounds.
• Understanding their solid solutions is crucial for materials design.

Purpose of the Study:

• To investigate the formation and stability of solid solutions between BA and TBA.
• To characterize the resulting co-crystal and its thermal properties.

Main Methods:

• Crystallization of BA-TBA mixtures.
• X-ray diffraction for structural analysis.
• Differential scanning calorimetry (DSC) for thermal analysis.

Main Results:

• Solid solutions of general formula BAxTBA1-x were formed for x < 0.8.
• A stable co-crystal, BA0.5TBA0.5, was identified, isomorphous with parent compounds.
• The BA0.5TBA0.5 co-crystal melts at 265 °C, higher than BA and TBA.
• Solid solutions with x < 0.5 convert to the BA0.5TBA0.5 co-crystal over time or with increased temperature.

Conclusions:

• The BA-TBA system exhibits complex solid solution behavior with a stable co-crystal formation.
• The co-crystal demonstrates improved thermal stability, suggesting potential applications in materials science.