Organic Crystals: Comprehensive Understanding of Proton States of Naftopidil Salts via XPS

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