Supramolecular architecture of picric acid and pyrazoles: syntheses, structural, computational and thermal studies

The salts comprised of picric acid [(OH)(NO2)3C6H2] and different ditopic pyrazoles PzR1,R2H (where R1 = R2 = H for 1, R1 = R2 = Me for 2, R1 = Ph, R2 = Me for 3) and 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (Me4bpz) 4 are reported. Due to presence of different substituents on pyrazole, each salt contains infinite three-dimensional structure held together by primary N–H…O, O–H…N, O–H…O hydrogen bonds and secondary C–H…O interactions. The structure and harmonic vibration frequencies of the complexes were calculated in terms of the density functional theory. The orientation of molecule remains same in both the solid phase and the gaseous phase. The thermal decomposition of these salts was studied by thermogravimetry and differential thermogravimetric analysis. Kinetic parameters were evaluated using model-fitting and isoconversional methods.