Structural, vibrational properties, and thermal stability of L-valine-fumaric acid cocrystal: An experimental study combined with DFT calculations

• The L-valine-Fumaric acid (LVAF) cocrystal crystallizes in a monoclinic system (space group C2) with eight molecules per unit cell. • DFT-B3LYP modeling validated the X-ray diffraction data, confirming the cocrystal structure. • TG/DTA and DSC revealed stability, a transition around 471 K, and a decomposition/melting peak at 505 K. • Raman spectroscopy at ambient temperature, combined with theoretical analysis, detailed the cocrystal's vibrational properties. • High-temperature X-ray diffraction (HTXD) and Raman spectroscopy revealed a progressive loss of crystallinity from 471 K. • HTXD exhibits a generalized amorphization pattern at 505–513 K. Molecular solids, particularly multicomponent crystals, have garnered substantial interest in recent decades due to their unique properties and versatile applications across scientific fields. The L-valine-fumaric acid (LVFA) cocrystal was synthesized using the slow evaporation method and characterized using experimental and theoretical techniques to elucidate its structural, vibrational, and thermal properties. Powder X-ray diffraction (PXRD) confirmed its monoclinic symmetry (C2) with eight molecules per unit cell, while DFT-B3LYP calculations showed excellent agreement with the experimental XRD data. Raman spectroscopy, supported by theoretical vibrational analysis, enabled precise mode assignments and revealed key molecular interactions. Thermal analysis (TGA/DTA) shows an endothermic peak at 505 K, related to loss of mass. DSC revealed a baseline shift at 437 K, an endothermic event at 471 K, and decomposition/melting of the material at 505 K. High-temperature X-ray diffractograms showed loss of crystallinity from 471 K, leading to an amorphous pattern at 513 K, findings corroborated by High-temperature Raman spectroscopy. The correlations between thermal events, XRD, and Raman analysis provide valuable insights into the stability and phase behavior of the LVFA cocrystal, contributing to the design of hydrogen-bonded molecular solids with tailored properties.