Synthesis, characterizations, molecular structure and DFT studies of 4-benzylidene-2-(2-chloro-phenyl)-5-methyl-2,4-dihydro-pyrazol-3-one

The title molecule 4-benzylidene-2-(2-chloro-phenyl)-5-methyl-2,4-dihydro-pyrazol-3-one, C₁₇H₁₃N₂OCl (I) is synthesized and characterized by IR, NMR and X-ray single crystal diffraction analysis. Molecular geometry, vibrational wave numbers, frontier molecular orbitals and Mulliken charges of the title compound have been calculated using density functional method B3LYP at 6-311g* basis set. Title compound crystallizes in the monoclinic space group P2_1/c with a = 10.343 (3) Å, b = 11.321 (3) Å, c = 12.486 (4) Å, β = 92.380 (5)°, V = 1460.8 (7) ų and Z = 4. The dihedral angles between the mean plane of chloro phenyl ring, phenyl ring with the mean plane of pyrazole ring are 65.91(15)° and 21.75(17)°, respectively. After optimization by DFT method, the twisting of the central pyrazole ring with chloro phenyl ring and phenyl ring turns out to be 51.96(16)° and 1.26(14)°, respectively. The drastic differences observed in the dihedral angle calculated after treating the molecule by DFT method support our observations that molecular packing is influenced by the collective effect of weak but significant C-H..N, C-Cl…π, C-H…Cl, C-H…O and π-π interactions in the solid state which are otherwise lacking in isolated state. The optimized geometric bond lengths, bond angles and torsional angles obtained by density function theory (DFT) show good agreement with experimental data. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. Pyrazole oxygen O₇ and chloro phenyl carbon C13 act as bifurcated donor and acceptor in half a dozen intermolecular interactions, thereby strengthening the molecular packing. (author)