A method of forming a transition metal containing films on a substrate by a cyclical deposition process is disclosed. The method may include: contacting the substrate with a first vapor phase reactant comprising a transition metal halide compound comprising a bidentate nitrogen containing adduct ligand; and contacting the substrate with a second vapor phase reactant. A method for supplying a transition metal halide compound comprising a bidentate nitrogen containing ligand to a reaction chamber is disclosed, along with related vapor deposition apparatus.