Cyclohexylammonium Hexaisothiocyanatonickelate(II) Dihydrate as a Single-Source Precursor for High Surface Area Nickel Oxide and Sulfide Nanocrystals

Cyclohexylammonium hexaisothiocyanatonickelate(II) dihydrate, (C6H11NH3)4[Ni(NCS)6]·2H2O, was synthesized, for the first time, by a four-step method in a yield of 95%. The compound was fully characterized by elemental microanalysis, Fourier transform infrared (FTIR), ultraviolet-visible-near infrared (UV-Vis-NIR), and nuclear magnetic resonance (NMR) spectroscopy and thermogravimetry. A single crystal X-ray diffraction (SXRD) gave the monoclinic space group P21/c with a = 15.8179 (5) Å, b = 10.6222 (3) Å, c = 13.8751 (4) Å, β = 109.362 (1)°, V = 2199.45 (11) Å3, Z = 2 (T = 293 K) for this novel hybrid organic–inorganic compound. The title compound was employed as a single-source precursor for the synthesis of mesoporous, high surface area nickel oxide (53 Å; 452 m2/g) and nickel sulfide (46 Å; 220 m2/g) via pyrolysis under air at 550 °C or helium atmosphere at 500 °C, respectively. X-ray powder diffraction (XRPD) demonstrated the nanocrystalline nature of both NiO and NiS with an average crystallite size of 16 and 54 nm, respectively. Scanning electron microscope (SEM) indicated the formation of agglomerated, quasi-spherical particles of nickel oxide and agglomerated flake-like structures of nickel sulfide. The high surface area, porosity, and nanocrystallinity of both NiO and NiS, obtained via this approach, are promising for a wide spectrum of applications.

Synthesis, X-ray Single-Crystal Structural Characterization, and Thermal Analysis of Bis(O-alkylxanthato)Cd(II) and Bis(O-alkylxanthato)Zn(II) Complexes Used as Precursors for Cadmium and Zinc Sulfide Thin Films

This work investigates tuning of the molecular structure of a series of O-alkylxanthato zinc and cadmium precursor complexes to enhance production of ZnS and CdS materials. The structures of several bis(O-alkylxanthato) cadmium(II) complexes (8-13) and bis(O-alkyl xanthato)zinc(II) complexes (18 and 19) are reported based on single crystal X-ray diffraction data. CdS and ZnS films were produced by the spin-coating of these metal complexes followed by their thermal decomposition to the corresponding metal sulfides. Thin films of CdS were deposited by spin-coating the bis(O-alkylxanthato) cadmium(II) precursors (7-13) on glass substrates, followed by annealing at 300 °C for 60 min. Thin films of ZnS were deposited by spin-coating bis(O-alkylxanthato) zinc(II) (14-20), followed by annealing at 200 °C for 60 min. The molecular complexes and solid state materials are characterized using a range of techniques including single-crystal X-ray diffraction, pXRD, EDS and XPS, DSC and TGA, UV-vis and PL spectroscopies, and electron microscopy. These techniques provided information on the influence of alkyl chain length on the thermal conditions required to fabricate metal sulfide films as well as film properties such as film quality, and morphology. For example, the obtained crystallite size of metal sulfide films formed is correlated to the hydrocarbon chain length of xanthate ligands in the precursor. The behavior of the complexes under thermal stress was therefore studied in detail. DTA and TGA profiles explain the relationship between hydrocarbon chain length, decomposition temperatures, and the energies required for decomposition. A higher decomposition temperature for complexes with longer hydrocarbon chains is observed compared to complexes with shorter hydrocarbon chains. Band-gap energies calculated from the optical absorption spectra alongside steady state and time-resolved photoluminescence studies are reported for CdS films.

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.

Aerosol-Assisted Chemical Vapor Deposition of ZnS from Thioureide Single Source Precursors

A family of 12 zinc(II) thoureide complexes, of the general form [{L}ZnMe], [{L}Zn{N(SiMe₃)₂}], and [{L}₂Zn], have been synthesized by direct reaction of the thiourea pro-ligands ⁱPrN(H)CS(NMe₂) H[L¹], CyN(H)CS(NMe₂) H[L³], ^tBuN(H)CS(NMe₂) H[L²], and MesN(H)CS(NMe₂) H[L⁴] with either ZnMe₂ (1:1) or Zn{N(SiMe₃)₂}₂ (1:1 and 2:1) and characterized by elemental analysis, NMR spectroscopy, and thermogravimetric analysis (TGA). The molecular structures of complexes [{L¹}ZnMe]₂ (1), [{L²}ZnMe]₂] (2), [{L³}ZnMe]_∞ (3), [{L⁴}ZnMe]₂] (4), [{L¹}Zn{N(SiMe₃)₂}]₂ (5), [{L²}Zn{N(SiMe₃)₂}]₂ (6), [{L³}Zn{N(SiMe₃)₂}]₂] (7), [{L⁴}Zn{N(SiMe₃)₂}]₂] (8), [{L¹}₂Zn]₂ (9), and [{L⁴}₂Zn]₂ (12) have been unambiguously determined using single crystal X-ray diffraction studies. Thermogravimetric analysis has been used to assess the viability of complexes 1-12 as single source precursors for the formation of ZnS. On the basis of TGA data compound 9 was investigated for its utility as a single source precursor to deposit ZnS films on silica-coated glass and crystalline silicon substrates at 150, 200, 250, and 300 °C using an aerosol assisted chemical vapor deposition (AACVD) method. The resultant films were confirmed to be hexagonal-ZnS by Raman spectroscopy and PXRD, and the surface morphologies were examined by SEM and AFM analysis. Thin films deposited from (9) at 250 and 300 °C were found to be comprised of more densely packed and more highly crystalline ZnS than films deposited at lower temperatures. The electronic properties of the ZnS thin films were deduced by UV-Vis spectroscopy to be very similar and displayed absorption behavior and band gap (E_g = 3.711-3.772 eV) values between those expected for bulk cubic-ZnS (E_g = 3.54 eV) and hexagonal-ZnS (E_g = 3.91 eV).

The deposition of cadmium selenide and cadmium phosphide thin films from cadmium thioselenoimidodiphosphinate by AACVD and the formation of an aromatic species

Aerosol-assisted chemical vapour deposition (AACVD) of Cd[(SPiPr2)(SePiPr2)N]2 yields hexagonal cadmium selenide and monoclinic cadmium phosphide films on glass substrates between 475 and 525 °C at different argon flow rates. The films were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS). All the results of XRD, EDAX and XPS are in agreement with our previous investigations on Cd[(SePiPr2)2N]2. A breakdown mechanism is proposed based on mass spectra and density functional theory calculations. A large peak at m/z 207 in the mass spectra, previously assigned by us as a new aromatic species, is also observed for this complex.

In situ study of the precursor conversion reactions during solventless synthesis of Co9S8, Ni3S2, Co and Ni nanowires

Synthesis of Co9S8, Ni3S2, Co and Ni nanowires by solventless thermolysis of a mixture of metal(ii) acetate and cysteine in vacuum is reported. The simple precursor system enables the nanowire phase to be tuned from pure metal (Co or Ni) to metal sulfide (Co9S8, Ni3S2) by varying the relative concentration of the metal(ii) acetate. The growth environment facilitates new insights through in situ characterization using field-emission scanning electron microscopy (FESEM) and thermogravimetric analysis with gas chromatography-mass spectrometry (TGA-GC-MS). Direct observation by FESEM shows the temperature at which nanowire growth occurs and suggests adatoms are incorporated into the base of the growing nanowire. TGA-GC-MS reveals the rates of precursor decomposition and identity of the volatilized ligand fragments during heat-up and at the nanowire growth temperature. Our results constitute a new approach for the selective fabrication of high quality Co9S8 and Ni3S2 nanowires and more importantly provides new understanding of precursor decomposition reactions that support symmetry-breaking growth in nanocrystals by heat-up synthesis.

Copper(i) tertiary phosphine xanthate complexes as single source precursors for copper sulfide and their application in the OER

Three heteroleptic bis(triphenylphosphine)copper(i) methyl pyridyl xanthate complexes used as single source precursors for copper sulfide and the resulting copper sulfides have been utilized for the electrocatalytic oxygen evolution reaction.

Precursor-mediated synthesis of Cu2−xSe nanoparticles and their composites with TiO2 for improved photocatalysis

Simple, but effective. Successful isolation and characterization of an intermediate during the reaction of ^tBu₂Se with Cu(TFA)₂ establishes the route for the formation of copper selenide NPs and Cu_2−xSe–TiO₂ composites as active photocatalysts.

On the phase control of CuInS2 nanoparticles from Cu-/In-xanthates

In this paper we report the synthesis characterisation of six In(iii) xanthate complexes that have been used for the synthesis of CuInS₂ nanoparticles in conjunction with a Cu(i)-xanthate – we have also demonstrated an ability to control the phase of the material through choice of solvent.

The deposition of thin films of cadmium zinc sulfide Cd1-x Zn x S at 250 °C from spin-coated xanthato complexes: a potential route to window layers for photovoltaic cells

Thin films of Cd_1-x Zn _x S (CZS) were prepared by a novel spin coating/melt method from cadmium ethylxanthato [Cd(C₂H₅OCS₂)₂] and zinc ethylxanthato [Zn(C₂H₅OCS₂)₂] in x ratios of 0-0.15 and of 1. A solution of the precursor(s) in THF was spin coated onto a glass substrate and then heated at 250 °C for 1 h under N₂. The thickness of the film formed can be controlled by varying the solution composition and/or the spin rate of the coating. A total metal precursor solution concentration of 50 mM was used in all cases. The films were characterized by p-XRD, SEM, EDX, ICP-AES, XPS, UV-Vis absorption spectroscopy, Raman spectroscopy and resistivity measurements. The band gaps of the films were between 2.35-2.58 and 3.75 eV (0 ≤ x ≤ 0.15 and at x = 1). The resistivity of Cd_1-x Zn _x S films was found to vary linearly with zinc contents, and the properties of the films suggest potential application to photovoltaics as window layers. This work is the first study to demonstrate Cd_1-x Zn _x S thin films by a spin coating/melt method from xanthato precursors.

A simple route to complex materials: the synthesis of alkaline earth – transition metal sulfides

A simple, low-temperature synthesis of a family of alkaline earth metal chalcogenide thin films is reported.

Aerosol-assisted CVD of cadmium diselenoimidodiphosphinate and formation of a new iPr2N2P3+ ion supported by combined DFT and mass spectrometric studies

Chemical vapour deposition and formation of a new ion involving Cd[(SePⁱPr₂)₂N]₂ is reported and discussed.

Electrically conducting palladium selenide (Pd4Se, Pd17Se15, Pd7Se4) phases: synthesis and activity towards hydrogen evolution reaction

Electrically conducting, continuous films of different phases of palladium selenides are synthesized by the thermolysis of single source molecular precursors.

Synthesis and structural characterization of monomeric mercury(ii) selenolate complexes derived from 2-phenylbenzamide ligands

The present work describes the synthesis and structural characterization of mercury selenolate complexes derived from 2-phenylbenzamide ligands and their isolation in monomeric form for the first time.

Synthesis of Crystalline Chalcogenides in Ionic Liquids

Crystalline chalcogenides belong to the most promising class of materials. In addition to dense solid-state structures, they may form molecular cluster arrangements and networks with high porosity, as in the so-called "zeotype" chalcogenidometalates. The high structural diversity comes along with interesting physical properties such as semi-/photoconductivity, ion transport capability, molecular trapping potential, as well as chemical and catalytic activity. The great interest in the development of new and tailored chalcogenides has provoked a continuous search for new and better synthesis strategies over the years. The trend has clearly been towards lower temperatures for both economic and ecological reasons as well as for better reaction control. This led to the application of ionic liquids as a designer-like medium for materials synthesis. In this Review, we summarize recent developments and present a survey of different chalcogenide families along with their properties.

Exploring the crystallization landscape of cadmium bis(N-hydroxyethyl, N-isopropyldithiocarbamate), Cd[S2CN(iPr)CH2CH2OH]2

Crystallization of Cd[S2CN(iPr)CH2CH2OH]2 from ethanol yields the coordination polymer [{Cd[S2CN(iPr)CH2CH2OH]2}·EtOH]∞ (1) within 3 h. When the solution is allowed to stand for another hour, the needles begin to dissolve and prisms emerge of the supramolecular isomer (SI), binuclear {Cd[S2CN(iPr)CH2CH2OH]2}2·2EtOH (2). These have been fully characterized spectroscopically and by X-ray crystallography. Polymeric 1 has 2-fold symmetry and features dithiocarbamate ligands coordinating two octahedral Cd atoms in a μ 2 κ 2-tridentate mode. Binuclear 2 is centrosymmetric with two ligands being μ 2 κ 2-tridentate as for 1 but the other two being κ 2-chelating leading to square pyramidal geometries. The conversion of the kinetic crystallization product, 1, to thermodynamic 2 is irreversible but transformations mediated by recrystallization (ethanol and acetonitrile) to related literature SI species, namely coordination polymer [{Cd[S2CN(iPr)CH2CH2OH]2}3·MeCN]∞ and binuclear {Cd[S2CN(iPr)CH2CH2 OH]2}2·2H2O·2MeCN, are demonstrated, some of which are reversible. Three other crystallization outcomes are described whereby crystal structures were obtained for the 1:2 co-crystal {Cd[S2CN(iPr)CH2CH2OH]2}2:2[3-(propan-2-yl)-1,3-oxazolidine-2-thione] (3), the salt co-crystal [iPrNH2(CH2CH2OH)]4[SO4]2{Cd[S2CN(iPr)CH2CH2OH]2}2 (4) and the salt [iPrNH2(CH2CH2OH)]{Cd[S2CN(iPr)CH2CH2OH]3} (5). These arise as a result of decomposition/oxidation of the dithiocarbamate ligands. In each of 3 and 4 the binuclear {Cd[S2CN(iPr)CH2CH2OH]2}2 SI, as in 2, is observed strongly suggesting a thermodynamic preference for this form.

Solution based CVD of main group materials

This critical review focuses on the solution based chemical vapour deposition (CVD) of main group materials with particular emphasis on their current and potential applications. Deposition of thin films of main group materials, such as metal oxides, sulfides and arsenides, have been researched owing to the array of applications which utilise them including solar cells, transparent conducting oxides (TCOs) and window coatings. Solution based CVD processes, such as aerosol-assisted (AA)CVD have been developed due to their scalability and to overcome the requirement of suitably volatile precursors as the technique relies on the solubility rather than volatility of precursors which vastly extends the range of potentially applicable compounds. An introduction into the applications and precursor requirements of main group materials will be presented first followed by a detailed discussion of their deposition reviewed according to this application. The challenges and prospects for further enabling research in terms of emerging main group materials will be discussed.

Intermolecular interactions in crystalline 1-(adamantane-1-carbonyl)-3-substituted thioureas with Hirshfeld surface analysis

The 1-acyl thiourea synthon is characterized through a complete Hirshfeld surface analysis for a series of six closely related 1-(adamantane-1-carbonyl) thioureas.

Soft template mediated synthesis of Bi–In–Zn–S and its efficient visible-light-driven decomposition of methylene blue

Bi–In–Zn–S nanostructures were successfully synthesized in PEG-PPG-PEG at various temperatures and are used as recyclable photocatalysts for the degradation of methylene blue under visible light (sunlight and 200 W tungsten lamp).

S4N4 as an intermediate in Ag2S nanoparticle synthesis

Hexamethyldisilazane assisted synthesis of Ag₂S nanoparticles is demonstrated. Mechanistic studies revealed that Ag₂S nanoparticles formed through S₄N₄ intermediates.

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.