Fluidized Bed Chemical Vapor Deposition on Hard Carbon Powders to Produce Composite Energy Materials.

Herein, we report a general route for the uniform coating of hard carbon (HC) powders via fluidized bed chemical vapor deposition. Carbon-based fine powders are excellent substrate materials for many catalytic and electrochemical applications but intrinsically difficult to fluidize and prone to elutriation. The reactor was designed to achieve as much retention of powders as possible, supported by a computational fluid dynamics study to assess the hydrodynamic behavior for varying gaseous flow rates. Solutions of the tin seleno- and thio-ether complexes [SnCl4{nBuSe(CH2)3SenBu}] and [SnCl4{nBuS(CH2)3SnBu}] were used as single source precursors and injected at high temperature into a fluidized bed of HC powders under nitrogen flow. The method allowed for the synthesis of HC-SnSx-SnSe2 composites at the gram scale with potential applications in electrocatalysis and sodium-ion battery anodes.

Synthesis, Characterization, and Computational Studies on Gallium(III) and Iron(III) Complexes with a Pentadentate Macrocyclic bis-Phosphinate Chelator and Their Investigation As Molecular Scaffolds for 18F Binding.

With the aim of obtaining improved molecular scaffolds for 18F binding to use in PET imaging, gallium(III) and iron(III) complexes with a macrocyclic bis-phosphinate chelator have been synthesized and their properties, including their fluoride binding ability, investigated. Reaction of Bn-tacn (1-benzyl-1,4,7-triazacyclononane) with paraformaldehyde and PhP(OR)2 (R = Me or Et) in refluxing THF, followed by acid hydrolysis, yields the macrocyclic bis(phosphinic acid) derivative, H2(Bn-NODP) (1-benzyl-4,7-phenylphosphinic acid-1,4,7-triazacyclononane), which is isolated as its protonated form, H2(Bn-NODP)·2HCl·4H2O, at low pH (HClaq), its disodium salt, Na2(Bn-NODP)·5H2O at pH 12 (NaOHaq), or the neutral H2(Bn-NODP) under mildly basic conditions (Et3N). A crystal structure of H2(Bn-NODP)·2HCl·H2O confirmed the ligand's identity. The mononuclear [GaCl(Bn-NODP)] complex was prepared by treatment of either the HCl or sodium salt with Ga(NO3)3·9H2O or GaCl3, while treatment of H2(Bn-NODP)·2HCl·4H2O with FeCl3 in aqueous HCl gives [FeCl(Bn-NODP)]. The addition of 1 mol. equiv of aqueous KF to these chloro complexes readily forms the [MF(Bn-NODP)] analogues. Spectroscopic analysis on these complexes confirms pentadentate coordination of the doubly deprotonated (bis-phosphinate) macrocycle via its N3O2 donor set, with the halide ligand completing a distorted octahedral geometry; this is further confirmed through a crystal structure analysis on [GaF(Bn-NODP)]·4H2O. The complex adopts the geometric isomer in which the phosphinate arms are coordinated unsymmetrically (isomer 1) and with the stereochemistry of the three N atoms of the tacn ring in the RRS configuration, denoted (N)RRS, and the phosphinate groups in the RR stereochemistry, denoted (P)RR, (isomer 1/RR), together with its (N)SSR (P)SS enantiomer. The greater thermodynamic stability of isomer 1/RR over the other possible isomers is also indicated by density functional theory (DFT) calculations. Radiofluorination experiments on the [MCl(Bn-NODP)] complexes in partially aqueous MeCN/NaOAcaq (Ga) or EtOH (Ga or Fe; i.e. without buffer) with 18F- target water at 80 °C/10 min lead to high radiochemical incorporation (radiochemical yields 60-80% at 1 mg/mL, or ∼1.5 µM, concentration of the precursor). While the [Fe18F(n-NODP)] is unstable (loss of 18F-) in both H2O/EtOH and PBS/EtOH (PBS = phosphate buffered saline), the [Ga18F(Bn-NODP)] radioproduct shows excellent stability, RCP = 99% at t = 4 h (RCP = radiochemical purity) when formulated in 90%:10% H2O/EtOH and ca. 95% RCP over 4 h when formulated in 90%:10% PBS/EtOH. This indicates that the new "GaIII(Bn-NODP)" moiety is a considerably superior fluoride binding scaffold than the previously reported [Ga18F(Bn-NODA)] (Bn-NODA = 1-benzyl-4,7-dicarboxylate-1,4,7-triazacyclononane), which undergoes rapid and complete hydrolysis in PBS/EtOH (refer to Chem. Eur. J. 2015, 21, 4688-4694).

Effects of surfactant head group modification on vertically oriented mesoporous silica produced by the electrochemically assisted surfactant assembly method.

Production of mesoporous silica films with vertically oriented pores has been a challenge since interest in such systems developed in the 1990s. Vertical orientation can be achieved by the electrochemically assisted surfactant assembly (EASA) method using cationic surfactants such as cetyltrimethylammonium bromide (C16TAB). The synthesis of porous silicas using a series of surfactants with increasing head sizes is described, from octadecyltrimethylammonium bromide (C18TAB) to octadecyltriethylammonium bromide (C18TEAB). These increase pore size, but the degree of hexagonal order in the vertically aligned pores reduces as the number of ethyl groups increases. Pore accessibility is also reduced with the larger head groups.

Synthesis, spectroscopic and structural properties of Sn(II) and Pb(II) triflate complexes with soft phosphine and arsine coordination.

Reaction of the divalent M(OTf)2 (M = Sn, Pb; OTf = CF3SO3) with soft phosphine and arsine ligands, L, where L = o-C6H4(ER2)2 (E = P, R = Me or Ph; E = As, R = Me), MeC(CH2ER2)3 (E = P, R = Ph; E = As, R = Me), PhP(CH2CH2PPh2)2 or P(CH2CH2PPh2)3, affords complexes of stoichiometry M(L)(OTf)2 as white powders, which have been characterised via elemental analysis, 1H, 19F{1H}, 31P{1H} and 119Sn NMR spectroscopy, with the expected 31P-119Sn and 31P-207Pb couplings clearly evident. The crystal structures of nine of these pnictine complexes are reported, in each case revealing retention of one or both OTf anions, which gives rise to a diverse range of coordination environments including monomers, as well as varying degrees of oligomerisation to form weakly associated (OTf-bridged) dimers, trimers and polymers. 19F{1H} NMR spectra indicate that the OTf is essentially anionic (dissociated) in solution. Anion metathesis of [M(OTf)2{MeC(CH2PPh2)3}] with Na[BArF] (BArF = B{3,5-(CF3)2C6H3}4) yields the corresponding [M{MeC(CH2PPh2)3}][BArF]2 salts, the crystal structures of all three (M = Ge, Sn, Pb) reveal pyramidal dications with discrete [BArF]- anions providing charge balance. Density functional theory (DFT) calculations on these [M{MeC(CH2PPh2)3}]2+ (M = Ge, Sn, Pb) dications using the B3LYP-D3 functional show the presence of a directional lone pair, which is a mixture of valence s and pz character, with the valence p-orbital character decreasing down group 14. Natural bond orbital (NBO) analysis also shows that the natural charge at the metal centre increases and the charge on the P centre decreases upon going down group 14.

Structural Diversity in Divalent Group 14 Triflate Complexes Involving Endocyclic Thia-Macrocyclic Coordination.

A highly unusual series of M(II) (M = Ge, Sn, Pb) complexes with endocyclic thioether macrocyclic coordination and with coordination numbers ranging from three to nine have been prepared by the reaction of [9]aneS3 (1,4,7-trithiacyclononane), [12]aneS4 (1,4,7,10-tetrathiacyclododecane), or [24]aneS8 (1,4,7,10,13,16,19,22-octathiacyclotetracosane) with M(OTf)2 (M = Sn and Pb; OTf = CF3SO3-) or with GeCl2·dioxane and 2 mol equiv of TMSOTf (Me3SiO3SCF3) in a mixture of anhydrous CH2Cl2 and MeCN. The isolated bulk products are characterized by 1H, 13C{1H}, 19F{1H}, and 119Sn{1H} NMR and IR spectroscopy, high-resolution ESI+ MS, and microanalytical data. Crystal structures are also reported for [M(L)][OTf]2 (M = Ge, Sn, Pb; L = [9]aneS3, [12]aneS4) and for [M([24]aneS8)][OTf]2 (M = Sn, Pb). In all cases, the ligand is bound in an endocyclic fashion, but the coordination environment and number are highly dependent on the group 14 ion, the macrocyclic ring size, and the number of S-donor atoms it presents. Solution NMR spectroscopic data suggest that the metal-macrocycle coordination is retained in solution but that the triflate anions are extensively dissociated on the NMR timescale. Density functional theory calculations on the [M([9]aneS3)]2+ and [M([12]aneS4)]2+ (M = Ge, Sn, Pb) dications reveal that the HOMO is centered on the group 14 atom as a directional "lone pair"; it also retains a significant amount of positive charge.

Flexible Memristor Devices Using Hybrid Polymer/Electrodeposited GeSbTe Nanoscale Thin Films.

We report on the development of hybrid organic-inorganic material-based flexible memristor devices made by a fast and simple electrochemical fabrication method. The devices consist of a bilayer of poly(methyl methacrylate) (PMMA) and Te-rich GeSbTe chalcogenide nanoscale thin films sandwiched between Ag top and TiN bottom electrodes on both Si and flexible polyimide substrates. These hybrid memristors require no electroforming process and exhibit reliable and reproducible bipolar resistive switching at low switching voltages under both flat and bending conditions. Multistate switching behavior can also be achieved by controlling the compliance current (CC). We attribute the switching between the high resistance state (HRS) and low resistance state (LRS) in the devices to the formation and rupture of conductive Ag filaments within the hybrid PMMA/GeSbTe matrix. This work provides a promising route to fabricate flexible memory devices through an electrodeposition process for application in flexible electronics.

Neutral and Cationic Complexes of Silicon(IV) Halides with Phosphine Ligands.

The reaction of SiI4 and PMe3 in n-hexane produced the yellow salt, [SiI3(PMe3)2]I, confirmed from its X-ray structure, containing a trigonal bipyramidal cation with trans-phosphines. This contrasts with the six-coordination found in (the known) trans-[SiX4(PMe3)2] (X = Cl, Br) complexes. The diphosphines o-C6H4(PMe2)2 and Et2P(CH2)2PEt2 form six-coordinate cis-[SiI4(diphosphine)], which were also characterized by X-ray crystallography, multinuclear NMR, and IR spectroscopy. Reaction of trans-[SiX4(PMe3)2] (X = Cl, Br) with Na[BArF] (BArF = [B{3,5-(CF3)2C6H3}4]) produced five-coordinate [SiX3(PMe3)2][BArF], but while Me3SiO3SCF3 also abstracted chloride from trans-[SiCl4(PMe3)2], the reaction products were six-coordinate complexes [SiCl3(PMe3)2(OTf)] and [SiCl2(PMe3)2(OTf)2] with the triflate coordinated. X-ray crystal structures were obtained for [SiCl3(PMe3)2][BArF] and [SiCl2(PMe3)2(OTf)2]. The charge distribution across the silicon species was also examined by natural bond orbital (NBO) analyses of the computed density functional theory (DFT) wavefunctions. For the [SiX4(PMe3)2] and [SiX3(PMe3)2]+ complexes, the positive charge on Si decreases and the negative charge on X decreases going from X = F to X = I. Upon going from [SiX4(PMe3)2] to [SiX3(PMe3)2]+, i.e., removal of X-, there is an increase in positive charge on Si and a decrease in negative charge on the X centers (except for the case X = F). The positive charge on P shows a slight decrease.

Increasing the Diameter of Vertically Aligned, Hexagonally Ordered Pores in Mesoporous Silica Thin Films.

The variation in pore size in mesoporous films produced by electrochemically assisted self-assembly (EASA) with the surfactant chain length is described. EASA produces a hexagonal array of pores perpendicular to the substrate surface by using an applied potential to organize cationic surfactants and the resultant current to drive condensation in a silica sol. Here, we show that a range of pore sizes between 2 and 5 nm in diameter is available with surfactants of the form [Me3NCnH2n+1]Br, with alkyl chain lengths between C14 and C24. The film quality, pore order, pore size, and pore accessibility are probed with a range of techniques.

Tungsten(VI) selenide tetrachloride, WSeCl4 - synthesis, properties, coordination complexes and application of [WSeCl4(SenBu2)] for CVD growth of WSe2 thin films.

WSeCl4 was obtained in good yield by heating WCl6 and Sb2Se3in vacuo. Green crystals grown by sublimation were shown by single crystal X-ray structure analysis to contain square pyramidal monomers with apical WSe, and powder X-ray diffraction (PXRD) analysis confirmed this to be the only form present in the bulk sample. Density functional theory (DFT) calculations using the B3LYP-D3 functional replicated the structure, identified the key bonding orbitals, and were used to aid assignment of the IR spectrum of WSeCl4. Reaction of WSeCl4 with ligands L gave [WSeCl4(L)] (L = MeCN, DMF, thf, py, OPPh3, 2,2'-bipy, SeMe2, SenBu2), whilst the dimers [(WSeCl4)2(µ-L-L)] were formed with L-L = Ph2P(O)CH2P(O)Ph2, 1,4-dioxane and 4,4'-bipyridyl. The complexes were characterised by microanalysis, IR and 1H NMR spectroscopy, and single crystal X-ray structures determined for [WSeCl4(L)] (L = OPPh3, MeCN, DMF) and [(WSeCl4)2(µ-L-L)] (L-L = 1,4-dioxane, 4,4'-bipyridyl). All except the 2,2'-bipy complex, which is probably seven-coordinate, contain six-coordinate tungsten with the neutral donor trans to WSe. Alkylphosphines, including PMe3 and PEt3, decompose WSeCl4 upon contact, forming phosphine selenides (SePR3). In contrast, the selenoether complexes [WSeCl4(SeMe2)] and [WSeCl4(SenBu2)] were isolated and characterised. The crystal structure of the minor W(VI) by-product, [(WSeCl4)2(µ-SeMe2)], was determined and using SMe2, a few crystals of the W(V) species, [{WCl3(SMe2)}2(µ-Se)(µ-Se2)], were obtained and structurally characterised. The isolated W(VI) complexes are compared with those of WOCl4 and WSCl4 and the combination of experimental and computational data are consistent with WSeCl4 being a weaker Lewis acid and its complexes significantly less stable than those of the lighter analogues, especially in solution. Low pressure chemical vapour deposition (LPCVD) using [WSeCl4(SenBu2)] in the range 660-700 °C (0.1 mmHg) produced highly reflective thin films, which were identified to be WSe2 by grazing incidence X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. XRD analysis of the thinner films revealed them to be highly oriented in the <00l> direction.

Neutral and cationic germanium(IV) fluoride complexes with phosphine coordination - synthesis, spectroscopy and structures.

The neutral complexes trans-[GeF4(PiPr3)2] and [GeF4(κ2-L)] (L = CH3C(CH2PPh2)3 or P(CH2CH2PPh2)3) are obtained from [GeF4(MeCN)2] and the ligand in CH2Cl2. Treatment of [GeF4(PMe3)2] with n equivalents of TMSOTf (Me3SiO3SCF3) leads to formation of the series [GeF4-n(PMe3)2(OTf)n] (n = 1, 2, 3), each of which contains six-coordinate Ge(IV) with trans PMe3 ligands and X-ray structural data confirm that the OTf groups interact with Ge(IV) to varying degrees. Unexpectedly, [GeF3(PMe3)2(OTf)] undergoes reductive defluorination in solution, forming the Ge(II) complex, [Ge(PMe3)3][OTf]2 (and [FPMe3]+). The bulkier PiPr3 leads to formation of the ionic [GeF3(iPr3P)2][OTf], containing a [GeF3(iPr3P)2]+ cation. [GeF4{o-C6H4(PMe2)2}], containing the cis-chelating diphosphine, also reacts with n equivalents of TMSOTf to generate [GeF4-n{o-C6H4(PMe2)2}(OTf)n] (n = 1, 2, 3). As for the PMe3 system, the trifluoride, [GeF3{o-C6H4(PMe2)2}(OTf)], is unstable to reductive defluorination in solution, producing the pyramidal Ge(II) complex [Ge{(o-C6H4(PMe2)2}(OTf)][OTf], whose crystal structure has been determined. The [GeF3{Ph2P(CH2)2PPh2}(OTf)] and [GeF2{Ph2P(CH2)2PPh2}(OTf)2], obtained similarly from the parent tetrafluoride complex, are poorly soluble, however their structures were confirmed crystallographically. The complexes in this work have been characterised via variable temperature 1H, 19F{1H} and 31P{1H} NMR studies in solution, IR spectroscopy and microanalysis and through single crystal X-ray analysis of representative examples across each series. Trends in the NMR and structural parameters are also discussed.

Low-Pressure CVD of GeE (E = Te, Se, S) Thin Films from Alkylgermanium Chalcogenolate Precursors and Effect of Deposition Temperature on the Thermoelectric Performance of GeTe.

The homologous series [GenBu3(EnBu)] (E = Te, Se, S; (1), (3) and (4)) and [GenBu2(TenBu)2] (2) have been synthesized as mobile oils in excellent yield (72-93%) and evaluated as single-source precursors for the low-pressure chemical vapor deposition (LPCVD) of GeE thin films on silica. Compositional and structural characterizations of the deposits have been performed by grazing-incidence X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray analysis, and Raman spectroscopy, confirming the phase purity and stoichiometry. Electrical characterization via variable-temperature Hall effect measurements is also reported. Given the strong interest in GeTe and its alloys for thermoelectric applications, variable-temperature Seebeck data were also investigated for a series of p-type GeTe films. The data show that it is possible to tune the thermoelectric response through intrinsic Ge vacancy regulation by varying the deposition temperature, with the highest power factor (40 µW/K2cm@629 K) and effective ZT values observed for the films deposited at higher temperatures.

Tin(IV) fluoride complexes with neutral phosphine coordination and comparisons with hard N- and O-donor ligands.

The reactions of trans-[SnF4(PMe3)2] with one, two or three equivalents of Me3SiO3SCF3 (TMSOTF), respectively, in anhydrous CH2Cl2 form six-coordinate [SnF4-n(PMe3)2(OTf)n] (n = 1-3), which have been characterised by microanalysis, IR and multinuclear NMR (1H, 19F{1H}, 31P{1H} and 119Sn) spectroscopy. The crystal structure of [SnF3(PMe3)2(OTf)] reveals the three fluorines are in a mer-arrangement with mutually trans PMe3 ligands. The multinuclear NMR spectra confirm this structure is retained in solution, and show that [SnF2(PMe3)2(OTf)2] has trans-phosphines, while [SnF(PMe3)2(OTf)3] has trans PMe3 groups and hence mer-triflate ligands. The [SnF4-n(PMe3)2(OTf)n] are unstable in solution and the decomposition products include [Me3PF]+ and the tin(II) complexes [Sn(PMe3)2(OTf)2] and [Sn3F5(OTf)], both of the latter identified by their crystal structures. The reaction of trans-[SnF4(PiPr3)2] containing the bulkier phosphine, with one and two equivalents of TMSOTf produced unstable mono- and bis-triflates, which the NMR data also suggest contain weakly coordinated triflate, [SnF3(PiPr3)2(OTf)] and [SnF2(PiPr3)2(OTf)2], again with axial phosphines, although some OTf dissociation from the former to give [SnF3(PiPr3)2]+ may occur in solution at room temperature. The new phosphine complexes of SnF4, trans-[SnF4(PiPr3)2] and (cis) [SnF4(κ2-triphos)] (triphos = CH3C(CH2PPh2)3) have also been fully characterised, including the crystal structure of [SnF4(κ2-triphos)]. Attempts to promote P3-coordination by further treatment of this complex with TMSOTf were unsuccessful. The [SnF4(L)2] (L = dmso, py, pyNO, DMF, OPPh3) complexes, which exist as mixtures of cis and trans isomers, react with one equivalent of TMSOTf, followed by addition of one equivalent of L, to form the ionic [SnF3(L)3][OTf] complexes, which were characterised by microanalysis, IR and multinuclear NMR spectroscopy. In nitromethane solution they are a mixture of mer and fac isomers based upon multinuclear NMR data (1H, 19F{1H}, 119Sn). Reaction of [SnF4(OPPh3)2] with two equivalents of TMSOTf and further OPPh3 produced [SnF2(OPPh3)4][OTf]2, which is a mixture of cis and trans isomers in solution. The crystal structure of [SnF2(OPPh3)4][OTf]2 confirms the trans isomer in the solid state, with the triflate ionic. These complexes are rare examples of fluorotin(IV) cations with neutral monodentate ligands.

Tungsten disulfide thin films via electrodeposition from a single source precursor.

We report a simple process for the electrodeposition of tungsten disulfide thin films from a CH2Cl2-based electrolyte using a tailored single source precursor, [NEt4]2[WS2Cl4]. This new precursor incorporates the 1 : 2 W : S ratio required for formation of WS2, and eliminates the need for an additional proton source in the electrolyte to remove excess sulfide. The electrochemical behaviour of [NEt4]2[WS2Cl4] is studied by cyclic voltammetry and electrochemical quartz crystal microbalance techniques, and the WS2 thin films are grown by potentiostatic electrodeposition.

Pyramidal Dicationic Ge(II) Complexes with Homoleptic Neutral Pnictine Coordination: A Combined Experimental and Density Functional Theory Study.

An unusual series of Ge(II) dicationic species with homoleptic phosphine and arsine coordination, [Ge(L)][OTf]2, L = 3 × PMe3, triphos (MeC(CH2PPh2)3), triars (MeC(CH2AsMe2)3), or κ3-tetraphos (P(CH2CH2PPh2)3) (OTf- = O3SCF3-) have been prepared by reaction of [GeCl2(dioxane)] with L and 2 mol equiv of Me3SiOTf in anhydrous CH2Cl2 (or MeCN for L = triars, triphos). X-ray crystal structures are reported for [Ge(PMe3)3][OTf]2, [Ge(triars)][OTf]2, and [Ge(κ3-tetraphos)][OTf]2, confirming homoleptic P3- or As3-coordination at Ge(II) in each case and with the discrete OTf- anions providing a charge balance. The Ge-P/As bond lengths are significantly shorter than those in neutral germanium(II) dihalide complexes with diphosphine or diarsine coordination. Solution NMR spectroscopic data indicate that the complexes are labile in solution. Using excess AsMe3 and [GeCl2(dioxane)] gives only the neutral product, [Ge(AsMe2)2(OTf)2], the crystal structure of which shows four coordination at Ge(II), via two As donor atoms and an O atom from two κ1-OTf- ligands; further weak, long-range intermolecular interactions give a chain polymer. The electronic structure of the [Ge(PMe3)3]2+ dication has been investigated using density functional theory (DFT) calculations. The computed geometrical parameters for this dication are in good agreement with the experimental X-ray crystallographic values in [Ge(PMe3)3][OTf]2. The results also indicate that the pyramidal arrangement of the [Ge(PMe3)3]2+ (computed P-Ge-P angle 96.8° at the B3LYP-D3 level) arises from a balance between electronic energy (Eelec) contributions, which favor a lower P-Ge-P angle, and nuclear-nuclear contributions (Enn), which favor a higher P-Ge-P angle, to the total energy (ETOT). An Atoms in Molecules (AIM) analysis reveals that one reason why Eelec decreases as the P-Ge-P angle decreases is because of C···H and H···H interactions between atoms on different CH3 groups. The stability of the [Ge(PMe3)3]2+ dication is enhanced by the distribution of a significant part of the positive charge on Ge2+ to the atomic centers of the PMe3 ligands. Similar results were obtained for [Ge(AsMe3)3][OTf]2, showing the tris-AsMe3 complex to be less stable compared to the PMe3 analogue. Related calculations were also performed for the neutral [Ge(PMe3)2(OTf)2] and [Ge(AsMe3)2(OTf)2] complexes.

Synthesis, properties and structural features of molybdenum(v) oxide trichloride complexes with neutral chalcogenoether ligands.

Complexes of oxotrichloromolybdenum(v) with neutral group 16 donor ligands, [MoOCl3(L-L)] (L-L = RS(CH2)2SR, R = iPr, Ph; MeS(CH2)3SMe; MeSe(CH2)2SeMe; MeSe(CH2)3SeMe), [{MoOCl2(EMe2)}2(µ-Cl)2] (E = S, Se, Te), [(MoOCl3)2{o-C6H4(EMe)2}]n (E = Se or Te) and [(MoOCl3)2{MeTe(CH2)3TeMe}]n, have been obtained by reaction of the ligands with [MoOCl3(thf)2] or MoOCl3 in either CH2Cl2 or toluene, and characterised by microanalysis, IR and UV-visible spectroscopy and magnetic measurements. The telluroethers are the first examples containing Mo in a positive oxidation state. X-ray crystal structures are reported for the six-coordinate fac-[MoOCl3{MeS(CH2)3SMe}], mer-[MoOCl3{iPrS(CH2)2SiPr}] and mer-[MoOCl3{MeSe(CH2)2SeMe}], as well as the six-coordinate chloride-bridged dimers, [{MoOCl2(SMe2)}2(µ-Cl)2] and [{MoOCl2(SeMe2)}2(µ-Cl)2]. The structure of the mixed-valence decomposition product, [MoIVCl{o-C6H4(TeMe)2}2(µ-O)MoVOCl4], was also determined. In toluene solution MoOCl4 is reduced by MeS(CH2)3SMe to produce the Mo(v) complex, [MoOCl3{ MeS(CH2)3SMe}]. Crystal structures of the previously unknown diphosphine analogue, [MoOCl3{Me2P(CH2)2PMe2}], and the mixed-valence derivative [MoIVCl{Me2P(CH2)2PMe2}2(µ-O)MoVOCl4] are also reported for comparison and help to clarify earlier contradictory literature reports. In contrast to the dimeric EMe2 complexes, [{MoOCl2(EMe2)}2(µ-Cl)2], PMe3 forms the monomeric complex, fac-[MoOCl3(PMe3)2].

Low temperature CVD of thermoelectric SnTe thin films from the single source precursor, [nBu3Sn(TenBu)].

This work has demonstrated that the single source precursor [nBu3Sn(TenBu)], bearing n-butyl groups and containing the necessary 1 : 1 Sn : Te ratio, facilitates growth of continuous, stoichiometric SnTe thin films. This single source CVD precursor allows film growth at significantly lower temperatures (355-434 °C at 0.01-0.05 Torr) than required for CVD from SnTe powder. This could be advantageous for controlling the surface states in topological insulators. The temperature-dependent thermoelectric performance of these films has been determined, revealing them to be p-type semiconductors with peak Seebeck coefficient and power factor values of 78 µV K-1 and 8.3 µW K-2 cm-1, respectively, at 615 K; comparing favourably with data from bulk SnTe. Further, we have demonstrated that the precursor facilitates area selective growth of SnTe onto the TiN regions of SiO2/TiN patterned substrates, which is expected to be beneficial for the fabrication of micro-thermoelectric generators.

Large-Area Electrodeposition of Few-Layer MoS2 on Graphene for 2D Material Heterostructures.

Heterostructures involving two-dimensional (2D) transition metal dichalcogenides and other materials such as graphene have a strong potential to be the fundamental building block of many electronic and optoelectronic applications. The integration and scalable fabrication of such heterostructures are of the essence in unleashing the potential of these materials in new technologies. For the first time, we demonstrate the growth of few-layer MoS2 films on graphene via nonaqueous electrodeposition. Through methods such as scanning and transmission electron microscopy, atomic force microscopy, Raman spectroscopy, energy- and wavelength-dispersive X-ray spectroscopies, and X-ray photoelectron spectroscopy, we show that this deposition method can produce large-area MoS2 films with high quality and uniformity over graphene. We reveal the potential of these heterostructures by measuring the photoinduced current through the film. These results pave the way toward developing the electrodeposition method for the large-scale growth of heterostructures consisting of varying 2D materials for many applications.

Thermoelectric Properties of Bismuth Telluride Thin Films Electrodeposited from a Nonaqueous Solution.

We report the thermoelectric properties of Bi2Te3 thin films electrodeposited from the weakly coordinating solvent dichloromethane (CH2Cl2). It was found that the oxidation of porous films is significant, causing the degradation of its thermoelectric properties. We show that the morphology of the film can be improved drastically by applying a short initial nucleation pulse, which generates a large number of nuclei, and then growing the nuclei by pulsed electrodeposition at a much lower overpotential. This significantly reduces the oxidation of the films as smooth films have a smaller surface-to-volume ratio and are less prone to oxidation. X-ray photoelectron spectroscopy (XPS) shows that those films with Te(O) termination show a complete absence of oxygen below the surface layer. A thin film transfer process was developed using polystyrene as a carrier polymer to transfer the films from the conductive TiN to an insulating layer for thermoelectrical characterization. Temperature-dependent Seebeck measurements revealed a room-temperature coefficient of -51.7 µV/K growing to nearly -100 µV/K at 520 °C. The corresponding power factor reaches a value of 88.2 µW/mK2 at that temperature.

Tertiary Phosphine and Arsine Complexes of Phosphorus Pentafluoride: Synthesis, Properties, and Electronic Structures.

The reaction of PMe3 or PPh3 with PF5 in anhydrous CH2Cl2 or hexane forms the white, moisture-sensitive complexes [PF5(PR3)] (R = Me, Ph). Similar reactions involving the diphosphines o-C6H4(PR2)2 afford the complexes [PF4{o-C6H4(PR2)2}][PF6]. The X-ray structures of [PF5(PR3)] and [PF4{o-C6H4(PMe2)2}][PF6] show pseudo-octahedral fluorophosphorus centers. Multinuclear NMR spectra (1H, 19F{1H}, 31P{1H}) show that in solution in CH2Cl2/CD2Cl2 the structures determined crystallographically are the only species present for [PF5(PMe3)] and [PF4{o-C6H4(PMe2)2}][PF6] but that [PF5(PPh3)] and [PF4{o-C6H4(PPh2)2}][PF6] exhibit reversible dissociation of the phosphine at ambient temperatures, although exchange slows at low temperatures. The complex 19F{1H} and 31P{1H} NMR spectra have been analyzed, including those of the cation [PF4{o-C6H4(PMe2)2}]+, which is a second-order AA'XX'B2M spin system. The unstable [PF5(AsMe3)], which decomposes in a few hours at ambient temperatures, has also been isolated and spectroscopically characterized; neither AsPh3 nor SbEt3 forms similar complexes. The electronic structures of the PF5 complexes have been explored by DFT calculations. The DFT optimized geometries for [PF5(PMe3)], [PF5(PPh3)], and [PF4{o-C6H4(PMe2)2}]+ are in good agreement with their respective crystal structure geometries. DFT calculations on the PF5-L complexes reveal the P-L bond strength falls with L in the order PMe3 > PPh3 > AsMe3, consistent with the experimentally observed stabilities, and in the PF5-L complexes, electron transfer from L to PF5 on forming these complexes also follows the order PMe3 > PPh3 ≈ AsMe3.