The interaction between the Hg2+and OPD could be testified from analysis of the simulated and the experimental FT-IR spectra as shown in Fig. 3. Computationally, for conformational explorations, the structure of [2C6H8N2+ Hg2+] was obtained by extensive DFT calculations for the probable complexes. Experimen-tally, the complex of [C6H8N2+ Hg2+] was characterized by FT-IR spectroscopy. The Hg N stretching at the frequencies 180 cm−1,which is the reported value [32,33], is observed in the simulated and the experimental FT-IR spectra as shown in Fig. 3(a). The optimized structure of [2C6H8N2+ Hg2+] is shown in Fig. 3(b). The simulated and experimental results confirm the formation of Hg N bond, which is the reason for preventing aggregation of the AuNPs induced by OPD.