Crystal structure, spectroscopy, DFT studies and thermal characterization of Cobalt(II) complex with 2-protonated aminopyridinium cation as ligand

• A novel cluster (2-HAMP)2[CoBr4] has been synthesized and fully characterized.
• The compound was characterized by X-ray, IR, Raman, TG-DTA techniques.
• Theoretical study was attempted by the Density Functional Theory.
• Charge transfer characteristics were examined by HOMO–LUMO.
• High temperature phase transitions were characterized by X-ray powder diffraction as a function of temperature.

Single crystals of a new organic–inorganic hybrid compound (2-HAMP)2[CoBr4], (2-HAMP = 2-protonated aminopyridinium cation) was synthesized and characterized by X-Ray diffraction at room temperature, DTA–TG measurement, FT-IR and FT-Raman spectroscopies and optical absorption. Its crystal structure is a packing of alternated organic and inorganic layers parallel to (a, b) plane. The different components are connected by a network of N/C–H⋯Br hydrogen bonds and halogen⋯halogen interactions. These hydrogen bonds give notable vibrational effects. Theoretical calculations were performed using density functional theory (DFT) for studying the molecular structure, vibrational spectra and optical properties of the investigated molecule in the ground state. The optimized geometrical parameters obtained by DFT calculations are in good agreement with single crystal XRD data. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) results complements with the experimental findings. The simulated spectra satisfactorily coincide with the experimental UV–Visible spectrum. The results show good consistent with the experiment and confirm the contribution of metal orbital to the HOMO–LUMO boundary. Thermal analysis studies indicate the presence of three phase transitions at 68, 125 and 172 °C, which are confirmed by X-ray powder diffraction as a function of temperature.

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