Optical Properties, Thermal Stability, and Biological Activity of a Non-Centrosymmetric Hybrid Compound 3,4-Diaminopyridinium Perchlorate (3,4-DAPP)

In this work, a new hybrid compound3,4-diaminopyridinium perchlorate with the formula (C5H8N3)ClO4abbreviated 3,4-DAPP was synthesized in aqueous solution at room temperature by the slow evaporation method. It crystallizes in the monoclinic system,with a non-centrosymmetric space group P21with the following parameters: a=5.1261 (9), b=9.3003 (17),c=8.6659 (16) Å and β=102.595 (7) °. However, the supramolecular crystal structure was built from perchlorate anions (ClO4)- and organic diaminopyridinum cations (C5H8N3)+connected with hydrogen bonds to form a three-dimensional network. Fourier transform infrared (FTIR) and Raman spectra indicate that the vibrational modes correspond to both inorganic and organic entities. According to Hirschfeld’s analysis, the crystal packing is mainly stabilizedby the presence of hydrogen bonds O⋯H (50%), as well as the crystal void analysis indicates the mechanical stability of the structure. Furthermore, the thermal behavior studied by thermogravimetric (TGA-DTA) and differential scanning calorimetry (DSC) appears to have good stability up to 280°C. Finally, the optical properties were investigated by UV-Vis absorption and photoluminescence spectroscopy along with density-functional theory DFT calculations, whichexhibit emission property, and a band gap energy of 3.9 eV.Additionally, biological activity tests revealed that 3,4-DAPP exhibited moderate antibacterial activity, particularly against Bacillus cereus, though it was less effective than 3,4-diaminopyridine (3,4-DAP) against several other bacteria, indicating that the perchlorate group in 3,4-DAPP may reduce its antimicrobial efficacy.