Organic Crystals:\nComprehensive Understanding of Proton\nStates of Naftopidil Salts via XPS

In this study, 18 Naftopidil (NFPD) binary salts were\nsynthesized\nand then analyzed via X-ray photoelectron spectroscopy (XPS). Among\nthese salts, nine known binary salts were initially investigated via\nSCXRD, where in every binary complex, the carboxylic acid (−COOH)\nproton is transferred to N of NFPD. Afterward, these nine NFPD salts\nwere examined via XPS, where N 1s binding energies of salts showed\na significant binding energy (BE) shift (2.1 to 2.6 eV) compared to\nthe neutral N 1s binding energy of NFPD. Later, nine novel complexes\nwere synthesized and explored via XPS. Interestingly, these new crystalline\nmaterials also manifest considerable N 1s BE shifts (1.9 to 2.4 eV)\ncompared to the neutral N 1s binding energy of NFPD. After a detailed\nevaluation of XPS experimental results, new complexes were predicted\nas NFPD salts, and SCXRD studies further confirmed these results.\nMoreover, all these crystalline materials were also characterized\nby powder X-ray diffraction and Fourier transform infrared (FT-IR)\nspectroscopy. Intermolecular interactions are further studied by Hirshfeld\nsurface analysis.