A structural comparative study of charge transfer compounds: Synthesis, crystal structure, IR, Raman-spectroscopy, DFT computation and hirshfeld surface analysis

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The present work focuses on the crystal structure analysis, vibrational spectroscopy investigation and DFT calculation. Two new charge transfer compounds; bis (creatininium) fumarate fumaric acid (I) and creatininium 3,5-dicarboxybenzoate monohydrate (II), have been synthesized, their Raman and IR modes of vibrations have been assigned and their crystal structures have been studied by means of single crystal X-ray diffraction. Complementary Hirshfeld surface analysis were carried out to investigate and quantify the contributions of the different intermolecular interactions within the crystal. This analysis revels that the main contributions in both compounds are provided by the O/H and H/H interactions that represent ~70 (for I) and ~75% (for II) of the total contributions to the Hirshfeld surface. The results of the theoretically predicted structural parameters and vibrational frequencies are in good agreements with the experimental investigations. These results show that both compounds exhibit similar features, however the energy gap between EHOMO and ELUMO obtained from the molecular orbital analysis indicates that compound (I) is characterized by a molecular structural more favourable for charge transfer.