Synthesis and properties of MoCl4 complexes with thio- and seleno-ethers and their use for chemical vapour deposition of MoSe2 and MoS2 films

Treatment of trans-[MoCl4(MeCN)(2)] with L (L = Me2S, Me2Se, THT, 1/2MeSCH(2)CH(2)SMe) in CH2Cl2 solution, or reaction of MoCl5 with excess L' (L' = (Bu2S)-Bu-n, (Bu2Se)-Bu-n, 1/2MeSCH(2)CH(2)SMe, 1/2(i)PrSCH(2)CH(2)S(i)Pr, 1/2MeSCH(2)CH(2)CH(2)SMe, 1/2MeSeCH(2)CH(2)CH(2)SeMe) in MeCN, produces the Mo(IV) complexes, [MoCl4(L)(2)] and [MoCl4(L')(2)], respectively, in good yield. The new complexes have been characterised by IR and UV-vis spectroscopy, elemental analysis and magnetic measurements, whilst crystal structure analyses of trans-[MoCl4(Me2S)(2)], cis-[MoCl4{RS(CH2)(2)SR}] (R = Me, Pr-i) and cis-[MoCl4{MeS(CH2)(3)SMe}] confirmed their identities and distorted octahedral geometries. The potential of [MoCl4(nBu(2)E)(2)] (E = S, Se) as the first examples of molybdenum halide derived single source CVD precursors for the growth of MoE2 thin films was first probed by TGA, which showed multi-step decomposition processes, with the masses of the final residues consistent with MoSe2 (E = Se) and MoCl4 (E = S), respectively. Low pressure CVD experiments conducted at 750 degrees C (E = S) and 525 degrees C (E = Se) gave silvery and golden yellow films, respectively. Grazing incidence and in plane XRD data confirmed these to be 2H-MoE2, whilst the texture of the MoSe2 was investigated using pole figure measurements. SEM and EDX data, optical and Raman data on the films are also reported.