Single-Source Routes to Cobalt Sulfide and Manganese Sulfide Thin Films

Diaryl dithiocarbamates: synthesis, oxidation to thiuram disulfides, Co(III) complexes [Co(S2CNAr2)3] and their use as single source precursors to CoS2

Air and moisture stable diaryl dithiocarbamate salts, Ar₂NCS₂Li, result from addition of CS₂ to Ar₂NLi, the latter being formed upon deprotonation of diarylamines by ⁿBuLi. Oxidation with K₃[Fe(CN)₆] affords the analogous thiuram disulfides, (Ar₂NCS₂)₂, two examples of which (Ar = p-C₆H₄X; X = Me, OMe) have been crystallographically characterised. The interconversion of dithiocarbamate and thiuram disulfides has also been probed electrochemically and compared with that established for the widely-utilised diethyl system. While oxidation reactions are generally clean and high yielding, for Ph(2-naphthyl)NCS₂Li an ortho-cyclisation product, 3-phenylnaphtho[2,1-d]thiazole-2(3H)-thione, is also formed, resulting from a competitive intramolecular free-radical cyclisation. To demonstrate the coordinating ability of diaryl dithiocarbamates, a small series of Co(III) complexes have been prepared, with two examples, [Co{S₂CN(p-tolyl)₂}₃] and [Co{S₂CNPh(m-tolyl)}₃] being crystallographically characterised. Solvothermal decomposition of [Co{S₂CN(p-tolyl)₂}₃] in oleylamine generates phase pure CoS₂ nanospheres in an unexpected phase-selective manner.

Dithiocarbamate Complexes as Single Source Precursors to Nanoscale Binary, Ternary and Quaternary Metal Sulfides

Nanodimensional metal sulfides are a developing class of low-cost materials with potential applications in areas as wide-ranging as energy storage, electrocatalysis, and imaging. An attractive synthetic strategy, which allows careful control over stoichiometry, is the single source precursor (SSP) approach in which well-defined molecular species containing preformed metal-sulfur bonds are heated to decomposition, either in the vapor or solution phase, resulting in facile loss of organics and formation of nanodimensional metal sulfides. By careful control of the precursor, the decomposition environment and addition of surfactants, this approach affords a range of nanocrystalline materials from a library of precursors. Dithiocarbamates (DTCs) are monoanionic chelating ligands that have been known for over a century and find applications in agriculture, medicine, and materials science. They are easily prepared from nontoxic secondary and primary amines and form stable complexes with all elements. Since pioneering work in the late 1980s, the use of DTC complexes as SSPs to a wide range of binary, ternary, and multinary sulfides has been extensively documented. This review maps these developments, from the formation of thin films, often comprised of embedded nanocrystals, to quantum dots coated with organic ligands or shelled by other metal sulfides that show high photoluminescence quantum yields, and a range of other nanomaterials in which both the phase and morphology of the nanocrystals can be engineered, allowing fine-tuning of technologically important physical properties, thus opening up a myriad of potential applications.

Understanding the role of zinc dithiocarbamate complexes as single source precursors to ZnS nanomaterials

Zinc sulfide is an important wide-band gap semi-conductor and dithiocarbamate complexes [Zn(S2CNR2)2] find widespread use as single-source precursors for the controlled synthesis of ZnS nanoparticulate modifications. Decomposition of [Zn(S2CNiBu2)2] in oleylamine gives high aspect ratio wurtzite nanowires, the average length of which was increased upon addition of thiuram disulfide to the decomposition mixture. To provide further insight into the decomposition process, X-ray absorption spectroscopy (XAS) of [Zn(S2CNMe2)2] was performed in the solid-state, in non-coordinating xylene and in oleylamine. In the solid-state, dimeric [Zn(S2CNMe2)2]2 was characterised in accord with the single crystal X-ray structure, while in xylene this breaks down into tetrahedral monomers. In situ XAS in oleylamine (RNH2) shows that the coordination sphere is further modified, amine binding to give five-coordinate [Zn(S2CNMe2)2(RNH2)]. This species is stable to ca. 70 °C, above which amine dissociates and at ca. 90 °C decomposition occurs to generate ZnS. The relatively low temperature onset of nanoparticle formation is associated with amine-exchange leading to the in situ formation of [Zn(S2CNMe2)(S2CNHR)] which has a low temperature decomposition pathway. Combining these observations with the previous work of others allows us to propose a detailed mechanistic scheme for the overall process.

Synthesis of ternary sulfide nanomaterials using dithiocarbamate complexes as single source precursors

We report the use of cheap, readily accessible and easy to handle di-isobutyl-dithiocarbamate complexes, [M(S2CNiBu2) n ], as single source precursors (SSPs) to ternary sulfides of iron-nickel, iron-copper and nickel-cobalt. Varying decomposition temperature and precursor concentrations has a significant effect on both the phase and size of the nanomaterials, and in some instances meta-stable phases are accessible. Decomposition of [Fe(S2CNiBu2)3]/[Ni(S2CNiBu2)2] at ca. 210-230 °C affords metastable FeNi2S4 (violarite) nanoparticles, while at higher temperatures the thermodynamic product (Fe,Ni)9S8 (pentlandite) results. Addition of tetra-isobutyl-thiuram disulfide to the decomposition mixture can significantly affect the nature of the product at any particular temperature-concentration, being attributed to suppression of the intramolecular Fe(iii) to Fe(ii) reduction. Attempts to replicate this simple approach to ternary metal sulfides of iron-indium and iron-zinc were unsuccessful, mixtures of binary metal sulfides resulting. Oleylamine is non-innocent in these transformations, and we propose that SSP decomposition occurs via primary-secondary backbone amide-exchange with primary dithiocarbamate complexes, [M(S2CNHoleyl) n ], being the active decomposition precursors.

Shining a light on transition metal chalcogenides for sustainable photovoltaics

Transition metal chalcogenides are an important family of materials that have received significant interest in recent years as they have the potential for diverse applications ranging from use in electronics to industrial lubricants. One of their most exciting properties is the ability to generate electricity from incident light. In this perspective we will summarise and highlight the key results and challenges in this area and explain how transition metal chalcogenides are a good choice for future sustainable photovoltaics.

Co9S8nanoflakes on graphene (Co9S8/G) nanocomposites for high performance supercapacitors

Co₉S₈/graphene nanocomposites (Co₉S₈/G) at various concentrations of graphene and Co₉S₈were prepared and tested for its electrochemical behaviour for supercapacitors.

COBALT(II)/NICKEL(II) COMPLEXES OF DITHIOACETYLACETONE [M(SacSac)2](M = Co, Ni) AS SINGLE SOURCE PRECURSORS FOR COBALT/NICKEL SULFIDE NANOSTRUCTURES

Cobalt(II)/Nickel(II) complexes of 4-thiopent-3-ene-2-thione (SacSac), [ M(SacSac) 2]( M = Co, Ni ) have been used as single source precursors (SSPs) for the preparation of cobalt/nickel sulfide thin films by aerosol-assisted chemical vapor deposition (AACVD). Cobalt or nickel sulfide nanoparticles were grown by thermal decomposition of the precursor in hot trioctylphosphine oxide (TOPO) or hexadecylamine (HDA). XRD analysis showed that all samples of cobalt or nickel sulfide are of the sulfur deficient phases ( Ni9S8, Co9S8, Ni7S6 , or Ni3S2 ). SEM and TEM analysis showed that nickel sulfide formed nanowires, nanorods and spheres; cobalt sulfide formed plate like structures and spheres. The chemical compositions of the nanoparticles can be controlled by varying temperature or the capping agents.

Single-molecule precursor-based approaches to cobalt sulphide nanostructures

Cobalt complexes of 1,1,5,5-tetramethyl-2,4-dithiobiuret, [Co{N(SCNMe(2))(2)}(3)] (1), and 1,1,5,5-tetraisopropyl-2-thiobiuret, [Co{N(SOCN(i)Pr(2))(2)}(2)] (2), have been synthesized and characterized. Both complexes were used as single-molecule precursors for the preparation of cobalt sulphide nanoparticles by thermolysis in hexadecylamine, octadecylamine or oleylamine. The powder X-ray diffraction pattern of as-prepared nanoparticles showed the hexagonal phase of Co(1-x)S from complex 1 and mixtures of cubic and hexagonal Co(4)S(3) from complex 2. Transmission electron microscopy images of material prepared from complex 1 showed spherical and trigonally shaped particles in the size range of 10-15 nm; whereas spheres, rods, trigonal prisms and pentagonally and hexagonally faceted crystallites were observed from complex 2. This observation is the first of the Co(4)S(3) phase in a nanodispersed form.

Ligand influence on the formation of P/Se semiconductor materials from metal-organic complexes

The complexes [Ni{(SeP(i)Pr(2))(2)N}(2)] (2), [Ni(Se(2)P(i)Pr(2))(2)] (), and [Co(Se(2)P(i)Pr(2))(2)] (4) were synthesised and the X-ray single crystal structures of (1) and (2) were determined. Thin films of nickel selenide, cobalt selenide and cobalt phosphide have been deposited by the chemical vapour deposition method using imidodiselenophosphinato-nickel(ii) (1), -cobalt(ii) [Co{(SeP(i)Pr(2))(2)N}(2)] (3), diselenophosphinato-nickel(ii) (2), -cobalt(ii) (4) and diselenocarbamato-nickel(ii) [Ni(Se(2)CNEt(2))(2)] (5), and -cobalt(iii) [Co(Se(2)CNEt(2))(3)] (6) precursors.