Chalcogenoether complexes of Nb(v) thio- and seleno-halides as single source precursors for low pressure chemical vapour deposition of NbS2 and NbSe2 thin films

Abstract

NbSCl₃ was obtained via reaction of NbCl₅ with S(SiMe₃)₂ in anhydrous CH₂Cl₂, whilst in MeCN solution the same reaction gives [NbSCl₃(MeCN)₂]. [NbSeCl₃(MeCN)₂] was obtained similarly from NbCl₅ with Se(SiMe₃)₂. The chalcogenoether complexes, [NbSCl₃(ER₂)] (E = S: R = Me, ⁿBu; E = Se: R = ⁿBu), were obtained from reaction of NbCl₅, ER₂ and S(SiMe₃)₂ in CH₂Cl₂. The structure of the [Nb₂S₂Cl₆(SMe₂)₂] reveals a Cl-bridged dimer with the SMe₂ ligands disposed syn. The Cl bridges are highly asymmetric, with the long Nb–Cl bond trans NbS. The complexes, [NbSCl₃(L–L)] (L–L = MeSCH₂CH₂SMe, MeS(CH₂)₃SMe, ⁱPrSCH₂CH₂SⁱPr, MeSe(CH₂)₃SeMe and ⁿBuS(CH₂)₃SⁿBu), were obtained from reaction of L–L with preformed [NbSCl₃(MeCN)₂]. The structures of the Me-substituted complexes reveal distorted octahedral monomers with the neutral ligands trans to S/Cl. Solution ¹H and ⁷⁷Se{¹H} NMR data showed that the neutral ligands are partially dissociated and undergoing fast exchange at ambient temperatures in CH₂Cl₂ solution, consistent with weak Lewis acidity for NbSCl₃. The complexes containing ⁿBu-substituted ligands have been used as single source precursors for low pressure chemical vapour deposition (CVD) of 3R-NbS₂ thin films. 2H-NbSe₂ thin films were also obtained via low pressure CVD using [NbSe₂Cl₃(SeⁿBu₂)]. The thin films were characterised by grazing incidence and in-plane XRD, pole figure analysis, scanning electron microscopy and energy dispersive X-ray analysis.