Synthesis and X-ray Characterization of 4,5-Dihydropyrazolyl-Thiazoles Bearing a Coumarin Moiety: On the Importance of Antiparallel pi-Stacking

The synthetic protocol and solid state characterization of two new coumarin-pyrazolylthiazole hybrids (1-2) are detailed in this manuscript. Synthesized compounds were characterized applying nuclear magnetic resonance, Fourier-transform infrared spectroscopy and single-crystal X-ray diffraction techniques. A detailed structural analysis of 3-(2-(5-(4-bromophenyl)-3-(4-fluorophenyl)-4,5-ciihydropyrazol-1-ypthiazol-4-yl)-2H-chromen-2-one (1) and 3-(2-(3,5-bis(4-bromophenyl)-4,5-ciihydropyrazol-1-yl)thiazol-4-yl)-2H-chromen-2-one (2) is reported along with a detailed description of the noncovalent interactions and their evaluation using Hirshfeld surface analysis, emphasizing the structure-directing role of C-H center dot center dot center dot O, Br center dot center dot center dot pi and pi-pi interactions. Finally, DFT energetics, molecular electrostatic potential (MEP), quantum theory of "atoms-in-molecules" (QTAIM) and non-covalent interaction plot (NClplot) index computations have been used to further investigate the relative importance of two different pi-stacking complexes observed in the solid state of both compounds, which are recurrent binding motifs in their crystal packing.