Thioether complexes of WSCl4, WOCl4 and WSCl3 and evaluation of thiochloride complexes as CVD precursors for WS2 thin films

Abstract

The red-brown [(WSCl₄)₂{μ-RS(CH₂)₂SR}] (R = Me, Ph, ⁱPr) and [(WSCl₄)₂{μ-MeS(CH₂)₃SMe}] have been made by reaction of WSCl₄ with the thioether in a 2 : 1 molar ratio, in anhydrous CH₂Cl₂ solution, and characterised by microanalysis, IR, UV/Vis and ¹H NMR spectroscopy. The X-ray structures of the four dithioether complexes reveal square pyramidal WSCl₄ units and bridging dithioethers with WS trans to thioether sulfur. Paramagnetic W(V) complexes, [WSCl₃{RS(CH₂)₂SR}] (R = Me, ⁱPr), have been made similarly using a 1 : ≥1 ratio of reactants or longer reaction times. The W(VI) complexes, [WSCl₄(SMe₂)] and [WSCl₄(SeMe₂)], are also described. Analogous complexes of WOCl₄, [(WOCl₄)₂{RS(CH₂)₂SR}] (R = Ph, ⁱPr), have been made similarly from WOCl₄, but reactions using MeS(CH₂)_nSMe (n = 2, 3) led to reduction to W(V), forming [WOCl₃{MeS(CH₂)_nSMe], both of which were identified crystallographically. Curiously, they are geometric isomers: [WOCl₃{MeS(CH₂)₃SMe}] has the dithioether trans Cl/Cl whereas in [WOCl₃{MeS(CH₂)₂SMe}] it is trans O/Cl. Remarkably, low pressure chemical vapour deposition (CVD) experiments using the dinuclear W(VI) species, [(WSCl₄)₂{ⁱPrS(CH₂)₂SⁱPr}], as a single source precursor produced thin films of 4H-WS₂, identified by grazing incidence X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy; the tungsten thiochloride complex is the first single source low pressure CVD precursor for WS₂. In contrast, the mononuclear W(V) complex, [WSCl₃{ⁱPrS(CH₂)₂SⁱPr}], does not deposit WS₂ under similar conditions.