Bidentate and tridentate coordination modes of bis(3-methylindolyl)-2-(1-methylimidazolyl)methane in complexes of aluminum and gallium

•A new indole-based ligand with an imidazole donor has been synthesized.•The ligand adopts a bidentate or tridentate coordination mode when bound to aluminum or gallium.•Bimetallic complexes are obtained from the ligand and two equivalents of trialkylaluminum.•Structures of three complexes and the ligand were confirmed by X-ray crystallography.