A series of pentavalent niobium and tantalum halide complexes with thio-, seleno- and telluro-ether ligands, [MCl5(E(n)Bu2)] (M = Nb, Ta; E = S, Se, Te), [TaX5(TeMe2)] (X = Cl, Br, F) and the dinuclear [(MCl5)2{o-C6H4(CH2SEt)2}] (M = Nb, Ta), has been prepared and characterised by IR, (1)H, (13)C{(1)H}, (77)Se, (93)Nb and (125)Te NMR spectroscopy, as appropriate, and microanalyses. Confirmation of the tantalum(V)-telluroether coordination follows from the crystal structure of [TaCl5(TeMe2)], which represents the highest oxidation state transition metal complex with telluroether coordination structurally authenticated. The Ta(V) monotelluroether complexes are much more stable than the Nb(V) analogues. In the presence of TaCl5 the ditelluroether, CH2(CH2Te(t)Bu)2, is decomposed; one of the products is the dealkylated [(t)BuTe(CH2)3Te][TaCl6], whose structure was determined crystallographically. Crystal structures of [(MCl5)2{o-C6H4(CH2SEt)2}] (M = Nb, Ta) show ligand-bridged species. The complexes bearing β-hydrogen atoms on the terminal alkyl substituents have also been investigated as single source reagents for the deposition of ME2 thin films via low pressure chemical vapour deposition. While the tantalum complexes proved to be unsuitable, the [NbCl5(S(n)Bu2)] and [NbCl5(Se(n)Bu2)] deposit NbS2 and NbSe2 as hexagonal platelets onto SiO2 substrates at 750 °C and 650 °C, respectively. Grazing incidence and in-plane X-ray diffraction confirm both materials adopt the 3R-polytype (R3mh), and the sulfide shows preferred orientation with the crystallites aligned predominantly with the c axis perpendicular to the substrate. Scanning electron microscopy and Raman spectra are consistent with the X-ray data.
. The thin films were characterised by grazing incidence and in-plane XRD, pole figure analysis, scanning electron microscopy and energy dispersive X-ray analysis.
The NbCl4 and BBr3, is a chain polymer with edge-linked NbBr6 octahedra and alternating long and short Nb-Nb distances, the latter ascribed to Nb─Nb bonds.
processes such as ion implantation can be used, but this approach tends to create undesirable defects, whose removal then requires additional annealing steps. Recently, lots of research attention has been focused on 2D materials, [1,2] as they not only exhibit great variety in electronic characteristics ranging from insulators to metals, but also possess unique properties related to their reduced dimensionality. While 2D materials can be doped with the same methods as bulk systems, there are approaches that are unique to them. Due to the surface-only geometry, the doping in 2D materials can also be attained by: 1) physical/chemical adsorption; 2) ionicliquid-gating; and 3) direct atomic substitution. [3,4] The surface adsorption and ionic-liquid-gating are basically equivalent to the implementation of charge transfer between the environment and the 2D materials, which are both very effective due the high surface to volume ratio of the 2D materials. However, the difficulties in integration of the system limit the practical applications of these approaches. The direct atomic substitution in 2D materials can be done via, e.g., sulfurization/selenization. [5] Alternatively, vacancies can be produced by irradiation [6,7] or thermal evaporation during annealing, [8] followed by the deposition of doping species. Direct substitution can also be achieved via ion implantation, but it is technically difficult, as it requires very low ion energies (below 100 eV) or needs an additional coating of buffer layer and The ORCID identification number(s) for the author(s) of this article can be found under
The coordination chemistry of neutral thio-, seleno-and telluroether ligands towards the hard s-block, f-block and higher oxidation state early d-block metals has developed significantly over the 15 or so years. This has revealed several hitherto unknown classes of complexes and new insights into the chemistries of these hard-soft metal-ligand combinations. This Perspective describes the synthetic routes used to access such complexes and draws out their key structural features and spectroscopic properties. Where appropriate, applications of these species are also highlighted, including their use as single source precursors for the chemical vapour deposition of semiconducting metal chalcogenide thin films and as pre-catalysts for olefin polymerisation reactions. IntroductionThioether and selenoether ligands, which are neutral sulfur and selenium donors respectively, were for many years viewed as modest σ-donor ligands that formed complexes with the softer later d-block elements in low or medium oxidation states, or with post transition metals such as silver or mercury.1,2Complexes of the early d-block metals were mostly limited to low valent organometallics or carbonyls. The chemistry of telluroethers was very little explored, in major part a reflection of their limited availability and, for the alkyl telluroethers in particular, their extremely malodorous nature. 2,3The R2Te ligands are also oxygen sensitive (in contrast to the air stable R2S or R2Se), modest reducing agents and prone to cleavage of the CTe bond upon reaction with some metal centres. Even today, their chemistry remains much less extensive than that of their lighter analogues. 4 Major developments in the syntheses and coordination chemistry of macrocyclic thioethers considerably extended the range and stability of complexes containing metal centres across the d-block. More recent work has resulted in complexes of chalcogenoethers with many of the p-block elements,
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