Synthesis, crystal structure, optoelectric properties and theoretical study of three perovskite-like iodobismuthate charge-transfer salts based on butylpyridinium

Three new perovskite-like iodobismuthate hybrids with two butylpyridinium cations, namely (BPY) 3 (Bi 2 I 9 ) ( 1 ), (BPY) 5 (Bi 2 I 11 ) ( 2 ) and (BMPY) 3 (Bi 2 I 9 ) ( 3 ) (BPY ​= ​1-butylpyridinium, BMPY ​= ​1-butyl-4-methylpyridinium), were synthesized by reacting of BiI 3 and butylpyridinium. Single-crystal X-ray diffraction analysis revealed that these three hybrids exhibit two types of di-nuclear cluster structures, face-sharing Bi 2 I 9 3− cluster for 1 and 3 , and vertex-sharing Bi 2 I 11 5− cluster for 2 . Their optical band gaps were determined as 2.06 ​eV( 1 ), 2.01 ​eV( 2 ), 1.86 ​eV( 3 ), respectively. DFT calculation reveals that their valence band tops and conduction band bottoms are composed of the states of iodine and pyridinium cations, respectively. Therefore these materials were classified as charge-transfer salts. Compared with similar iodobismuthates, their band gaps are significantly reduced. In addition, it is found that the band gaps should be affected by supramolecular interaction between cations in 2 and also by the conformational multiplicity of cations in structure 3 . Photocurrent response test showed that these charge-transfer salts have rapid and consistent photocurrent response. This result indicated their potential applications as a photocatalyst or a photovoltaic absorber.