Investigation of stable solid diazonium salt by molecular structure, Hirshfeld surface analysis, optical and electrochemical studies, and applications

The title compound is a new pyrazolone derivative which was synthesized starting from p -sulphophenyl-3-methyl-5-pyrazolone ( 1 ) by nitrosation at low temperature to afford the corresponding p -sulphophenyl-3-methyl-4-nitroso-5-pyrazolone which can exist both in nitroso ( 2a ) and oxime tautomeric forms ( 2b ). Reduction of the latter using zinc with hydrochloric acid furnished the 4-amino- p -sulphophenyl-3-methyl-5-pyrazolone ( 3 ). The diazotization of ( 3 ) under careful control of temperature and pH afforded the p -sulphophenyl-3-methyl-5-pyrazolone diazonium salt ( 4 ) which was re-crystallized from acidified ethanol to afford crystal suitable for X-ray studies. UV–visible spectrum and cyclic voltammetric studies were also carried out indicating λ max at 420 nm and HOMO-LUMMO energy gap was also calculated ( E g ) of 2.95 eV. The molecular and crystal structures of the compound were clarified by single crystal X-ray diffraction indicated that it crystallizes as the sodium salt in the triclinic space group P -1 , with the 4-azo-pyrazolone and the sulphophenyl groups being nearly coplanar. To get an insight to the intermolecular interactions in the crystal, a Hirshfeld surface analysis was also carried out. Graphical abstract