This paper describes the synthesis of three iso-structural Zn(II), Cd(II), and Hg(II) complexes with 1-benzyl-2-phenyl-1H-benzimidazole (BPB). Single crystal X-ray determination of CdBPB and HgBPB were done along with Structural analysis of ZnBPB by X-ray powder diffraction data. Raman spectroscopic studies for BPB and the metal complexes were done. 1H and 13C NMR data for the free BPB were also collected. The study further included the photoluminescence behaviour of the three metal complexes.
The authors mention BFB many times, but they have not given the full name of the ligand. The only guess can be made from “The BFB can also be obtained using basic solution  or microwave radiation ” mentioned in section 2.2.
The 1H and 13C NMR data for the free BPB can be reproduced easily with accurate assignments as given in table 3. The physical characteristics of the ligand and the complexes and their respective melting points can be reproduced.
Photoluminescence spectra in solid state do show the behaviour discussed in section 3.4, but in methanolic solution, the emission at 396 nm is still visible. So the explanation “All observed peaks can be attributed to π→π* intra-ligand or ligand-to-metal charge transfer mechanisms” does not hold.
Photoluminescence spectra should be studied in methanolic solution. It is recommended to assign the emission band at 396 nm as ligand-to-metal charge transfer only.
Photoluminescence spectra and X-ray data for the ligand should be tallied in order to find any relation between π- π stacking and fluorescence.