Treatment of BiBr3 with super bulky [(IPaul)Se] (L1) ([(IPaul)Se] = 1,3-bis(2,4-methyl-6-diphenyl phenyl)imidazole selone) or IPr*Se (L2) (IPr*Se = 1,3-bis(2,6-diphenylmethylphenyl)imidazole selone) in toluene afforded the dinuclear complex [(L1)BiBr2(µ-Br)]2 (1) and mononuclear complex [(L2)BiBr3] (2), whose structures have been determined by an X-ray crystallographic study. The complexes were characterized by a combination of 1H NMR and 13C{1H} NMR spectroscopy. The thermal stability of 1 and 2 was compared using TGA. The steric controlled super bulky ligand systems allow for the first structural isolation of a novel super bulky dinuclear complex 1 with edge shared octahedral geometry and mononuclear super bulky complex 2 with mono capped seesaw geometry. The sterically more crowded complex 2 showed the long Bi-Se bond distance (3.192(3) Å) compared to 1 (2.902(5) Å). © 2020 Elsevier Ltd