Coordination complexes and applications of transition metal sulfide and selenide halides

Metal chalcogenide halides are less studied analogues of metal oxide halides, where the oxido-group is replaced by heavier Group 16 elements, specifically sulfur, selenium or tellurium. This article reviews the chemistry of neutral ligand complexes of molecular chalcogenide halides of the d-block metals. The majority of these complexes contain the higher oxidation states of niobium, tantalum and tungsten, with more limited examples of titanium, molybdenum and vanadium compounds. The synthesis, structures and properties are described, and areas in need of further study identified. The recent application of several examples as low pressure chemical vapour deposition reagents for the production of thin films of semiconducting metal dichalcogenide materials is also discussed.