The preparation of a bismuth-based complex and the influence of double protonation

Abstract

Bismuth as a relatively non-toxic and inexpensive metal has a wide range of applications. There are numerous compounds based on bismuth that exhibit excellent semiconductive, photochromic, intensely luminous, and other properties. In this work, we synthesized a new bismuth-based complex (C10H8N2BiCl4, named complex 1) by a hydrothermal method. The crystal structure of complex 1 is resolved using single-crystal X-ray diffraction. When replacing water by methanol as solvent, the color of the obtained crystals (denoted as complex 2) changes from colorless to pink. The analysis of IR and XPS suggests that partial double protonation of the pyridine nitrogen occurs in complex 2. Because of partial double protonation, complex 2 displays visible light absorption and stronger fluorescence intensity. Further investigation found that complex 1 could change its color from colorless to pink in the presence of formic acid and acetic acid, suggesting that complex 1 can be used as formic acid (HCOOH) and acetic acid (CH3COOH) sensors. This work provides new insights into the exploration of bismuth-based complexes and provides a new way to broaden light absorption and enhance luminescence.