Single crystal XRD, vibrational spectra, quantum chemical and thermal studies on a new semi-organic crystal: 4-Aminium antipyrine chloride

• New semiorganic single crystal of 4-aminium antipyrine chloride was grown by slow evaporation method.
• The crystal and molecular structure identified by single crystal XRD.
• Theoretical calculation was attempted by the HF and DFT method.
• The chemical hardness, electro-negativity and chemical potential of the molecule were carried out by HOMO – LUMO plot.
• Thermal stability was analysed by TG/DTA studies.

The new semi-organic crystal of 4-aminium antipyrine chloride was grown as a single crystal by slow evaporation solution growth method. The crystal and molecular structure of the grown crystal was determined by single crystal diffraction techniques. The single crystal XRD studies reveal that the phenyl ring and pyrazolone ring of the cation has been inclined at an angle of 52.3 (1)°. The molecular aggregations were stabilized through intricate three dimensional hydrogen bonding network formed by the classical N–H⋯O and N–H⋯Cl hydrogen bonds. The cationic dimer R22(10) motif formed through N–H⋯O intermolecular hydrogen bonds was observed around the inversion center of the unit cell. The amino group from the cation and the chlorine anion was linked through N–H⋯Cl intermolecular hydrogen bond leading to a R24 (8) ring motif. These two ring motifs were extended along the a-axis of the unit cell and forms a hydrophilic layer at z = 0 and 1, which is sandwiched between the hydrophobic layer at z = 1/2. Geometry optimization of the molecules was done by Density Functional Theory (DFT) using the B3LYP function and Hartree–Fock (HF) level with 6-311++G(d,p) basis set. The optimized molecular geometry and computed vibrational spectra were compared with experimental results which show a significant agreement. The natural bond orbital (NBO) analysis was carried out to interpret hyperconjucative interaction and intramolecular charge transfer (ICT). The chemical hardness, electro-negativity and chemical potential of the molecule were carried out by HOMO-LUMO plot. The lower band gap value of the frontier orbitals shows the possible bioactivity of the molecule.

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