Synthesis and characterization of Group 6 thiourea complexes for use as single-source precursors for metal disulfides
A series of Group 6 thiourea complexes was synthesized to assess their utility as single-source precursors for the production of metal disulfides. The majority of this study focuses on the coordination chemistry of tetramethylthiourea (TMTU) complexes of the form [M(CO)6-n(TMTU)n] where n = 1 or 2 and M = Mo or W. Attempted synthesis of the tris-TMTU complex, fac-[Mo(CO)3(TMTU)3], is also discussed. A section concerning bidentate cyclic thioureas and selenoureas is described in an appendix. Both mono-TMTU complexes are octahedral and demonstrate monodentate thiourea coordination with sulfur as the donor atom. The bis-TMTU complexes are also octahedral and display cis disposition of the thiourea ligands in the solid state. In solution, the bis-thiourea complexes undergo dissociation of one TMTU ligand to generate dimeric complexes. The mono- and bis-tetramethylthiourea complexes were thermolytically decomposed successfully in the solid state to afford metal disulfides, MoS2 and WS2, with typical recoveries of 30-40% for mono precursors and 80-90% for bis precursors. Complexes such as these represent an appealing approach to the production of metal disulfides at relatively mild conditions, with all examples providing the desired material after being heated at 300 °C for 1 hour in an inert atmosphere. They also offer the particular benefit of being soluble in volatile organic solvents, which contrasts with the majority of published MoS2 preparations which rely on either chemical vapor deposition or dip-coating using non-volatile solvents.