Low-energy electron scattering by methane,arsine and phosphine

We present cross sections for the elastic scattering of low-energy electrons by phosphine (PH₃) and arsine (AsH₃), and for electron-impact excitation of the (1t ₂ 3sa ₁)³ T ₂ and¹ T ₂ states in methane (CH₄). These results were calculated using the Schwinger multichannel method as implemented on distributed-memory parallel computers. The PH₃ and AsH₃ cross sections show a pronounced low-energy shape resonance which may provide a pathway to dissociative attachment. The^1,3 T ₂ cross sections for CH₄ correlate fairly well with recent measurements of CH₂ production via electron-impact dissociation of methane.Contribution No. 8587     

Single-Source III/V Precursors: A New Approach to Gallium Arsenide and Related Semiconductors

Until recently, the production of gallium arsenide, indium phosphide, and related compound semiconductors has fallen in the domain of the materials scientist and the electrical engineer. By clever use of classical chemistry, exemplified by the thermal reaction of Me₃Ga and AsH₃, it is possible to make semiconductors on a commercial scale. However, there are some drawbacks associated with the existing methodology, including the environmental and health hazards of handling pyrophoric and toxic starting materials as well as stoichiometry control problems and undesirable side reactions. Can the synthetic inorganic and organometallic chemist play a useful role in this important area by designing and developing new reagents for the production of semiconductor materials? We believe the answer is yes, and in this article we discuss a new approach to the preparation of GaAs and InP thin films based on single-source precursors. These compounds feature strong σ-bonding between the group III and V elements, together with substituents that are capable of facile thermal elimination. The III/V precursors are more stable toward air and moisture and considerably less toxic than either adducts or mixtures of group III and V compounds.     

In-vitro prenatal toxicity of trimethylarsine,trimethylarsine oxide and trimethylarsine sulfide

The embryolethality and the embryotoxicity of trimethylarsine, trimethylarsine oxide and trimethylarsine sulfide were investigated employing Sprague–Dawley rat embryos with intact yolk sacs. The embryos were removed on day 11 of gestation and grown in a culture medium (Way-mouth's 725/1) spiked with the arsenic compounds to concentrations in the range 4–100 mM in the presence or absence of rat liver (S-9) homogenate. After 24 h the yolk-sac circulation and heart beat were monitored (indicator of embryolethality), the crown-to-rump lengths were measured, the neural structures (somites) counted, and the development of the limb buds evaluated (indicators of embryotoxicity). At a trimethylarsine concentration of 18.7 mM 78% of the embryos were dead when no S-9 was present. In the presence of S-9 all embryos survived but were necrotic and malformed. Signs of embryotoxicity were observed at concentrations of 18.7 and 9.3 mM. At the 4.7 mM concentration the embryos grew as well as the control embryos. Trimethylarsine oxide v as lethal at 100 mM and severely embryotoxic at 50 and 25 mM. At all but the lowest concentration (4.5 mM) the embryos looked sick, and were frequently necrotic, deformed and underdeveloped. Trimethylarsine sulfide exhibited severe embryotoxicity at 50 mM concentration in the absence and in the presence of S-9. Signs of acute toxicity were observable at 9 mM concentrations of trimethylarsine and trimethylarsine oxide. Compared with other environmental toxicants that show effects at concentrations orders of magnitude smaller, these arsenic compounds cannot be classified as very toxic.     

Metal localized emission in d6 phosphine and arsine complexes

Emission and absorption spectra (liquid nitrogen temperature) are reported for the bis diphenylphosphinoethane (dppe) and bis diphenylarsinoethane complexes of the Rh(III) and Ir(III) d⁶ ions. No emission was detected for the analogous Ru(II) complexes. The emission observed is broad, structureless and exhibits a large Stokes shift. Emission lifetimes are all ≈ μsec magnitude. From these data the emission can be assigned as a metal localized ³E → ¹A₁ emission.     

On the aromaticity and Meisenheimer rearrangement of strained heterocyclic amine, phosphine, and arsine oxides

A theoretical investigation (AIM and ELF analyses together with NMR chemical shifts) has been conducted for three-membered heterocycle (N, P, and As) oxides. An aromatic stabilization was found for the P and As rings. However, the N derivatives displayed a net negative hyperconjugation in the N-O bond formation, without ring aromaticity observed for their electronic properties. The calculated delta(C) and delta(H) shifts also supported the ring delocalization for the P and As unsaturated heterocycle oxides (delta(C) approximately 165 and delta(H) approximately 9 ppm). In addition, these values for 1H-azirine oxide resembled standard C=C double bond values (delta(C) approximately 130 and delta(H) approximately 7 ppm). The different behavior for the N oxides was also observed in their Meisenheimer rearrangement (MR). All the reaction paths, yielding the corresponding hydroxyl structures, were exothermic (G2 method). However, the N derivatives showed the lowest values for activation enthalpy, DeltaH(). The C=C bond influence in the MR was slight, with the same DeltaH values for the saturated and unsaturated paths. This rearrangement for the P and As oxides yielded TSs closer to the reactives; however, the corresponding TSs resembled the products for the N-derivatives. The different reaction paths have been examined by their corresponding AIM and ELF analyses at the B3LYP/6-311G level.     

Ligating properties of tertiary phosphine/arsine sulphides or selenides,part V. Complexes of ditertiaryphosphine disulphides and diselenides with platinum(II) and platinum(IV) halides

Summary Platinum(IV)/platinum(II) chloride and bromide form 1 : 1, 1 : 2 or 3 : 2 (metal: ligand) addition compounds with 1,2-ethylene-, 1,3-propylene-and 1,4-butylene-bisdiphenyl-phosphine sulphide or selenide and 1,6-hexamethylene-bisdiphenylphosphine selenide. The adducts have been characterized by elemental analysis, i.r. and reflectance spectra, and molar conductance data. All adducts have been assigned bridged square planar or octahedral arrangements around platinum(II) or platinum(IV) ions respectively. Both oxidation states of platinum conform to class b behaviour with respect to the soft donor sulphur and selenium atoms of the ligands.Reprints of this article are not available.     

Synthesis, characterization, and reactivity of half-sandwich Ru(II) complexes containing phosphine, arsine, stibine, and bismutine ligands

The synthesis and some reactions of the Ru(II) and Ru(IV) half-sandwich complexes [RuCp(EPh₃)(CH₃CN)₂]⁺ (E=P, As, Sb, Bi) and [RuCp(EPh₃)(η³-C₃H₅)Br]⁺ have been investigated. The chemistry of this class of compounds is characterized by a competitive coordination of EPh₃ either via a RuE or a η⁶-arene bond, where the latter is favored when the former is weaker, that is in going down the series. Thus in the case of Bi, the starting material [RuCp(CH₃CN)₃]⁺ does not react with BiPh₃ to give [RuCp(BiPh₃)(CH₃CN)₂]⁺ but instead gives only the η⁶-arene species [RuCp(η⁶-PhBiPh₂)]⁺ and [(RuCp)₂(μ-η⁶,η⁶-Ph₂BiPh)]²⁺. Similarly, the EPh₃ ligand can be replaced by an aromatic solvent or an arene substrate. Thus, the catalytic performance of [RuCp(EPh₃)(CH₃CN)₂]⁺ for the isomerization of allyl-phenyl ethers to the corresponding 1-propenyl ethers is best with E=P, while the conversion drops significantly using the As and Sb derivatives. By the same token, only [RuCp(PPh₃)(CH₃CN)₂]⁺ is stable in a non-aromatic solvent, whereas both [RuCp(AsPh₃)(CH₃CN)₂]⁺ and [RuCp(SbPh₃)(CH₃CN)₂]⁺ rearrange upon warming to [RuCp(η⁶-PhEPh₂)]⁺ and related compounds. In addition, the potential of [RuCp(EPh₃)(CH₃CN)₂]⁺ as precatalysts for the transfer hydrogenation of acetophenone and cyclohexanone has been investigated. Again aromatic substrates are clearly less suited than non-aromatic ones due to facile η⁶-arene coordination leading to catalyst's deactivation.     

Synthesis,structure, and redox properties of the extremely crowded triarylpnictogens: tris(2,4,6-triisopropylphenyl)phosphine,arsine, stibine,and bismuthine

A series of the extremely crowded triarylpnitogens, tris(2,4,6-triisopropylphenyl)phosphine (1), arsine (2), stibine (3), and bismuthine (4), were synthesized by the reaction of 2,4,6-triisopropylphenylcopper(I) with the corresponding pnictogen trichlorides. Introducion of the three bulky aryl groups resulted in the unusual structures and redox properties, which were studied by X-ray crystallography and cyclic voltammetry. The triarylpnictogens 1, 2, and 3 had extremely large bond angles around pnictogen atoms (1: 111.5 degrees , 2: 109.2 degrees , 3: 106.7 degrees ), and not only 1 and 2, but also stibine 3 displayed a reversible redox wave in the cyclic voltammograms at very low potentials (1: 0.16 V, 2: 0.50 V, 3: 0.57 V vs Ag/Ag+), which suggests considerable stability of the corresponding cation radicals.     

Chemistry of iron complexes. Part V. Electron spin resonance spectra of some iron(III) complexes and X-Ray diffraction (powder) data of iron(II) complexes employing tertiary phosphine/arsine oxides

Summary Electron spin resonance spectra (X-band, 9.3 GHz) of iron(III) chloride complexes with tri-p-tolylarsine oxide (T₃AO), methylenebis(diphenylphosphine oxide) (mdpo) and 1,4-tetramethylenebis(diphenylphosphine oxide) (tmdpo) support their structures as [Fe(L-L)₂Cl₂][FeCl₄] (L-L=mdpo or tmdpo) and [Fe(T₃AO)₂Cl₂(OH₂)₂][FeCl₄]2H₂O. The x-ray powder diffraction patterns of some iron(II) iodide complexes with mdpo, tmdpo, dmdpo, dmdao and tmdao [dmdpo-1,2-dimethylenebis(diphenylphosphine oxide); dmdao and tmdao are the arsine analogs of dmdpo and tmdpo] show that the complexes are crystalline but not isomorphous.     

(H2NC4H8NCH2CH2NH2)(HNCH2CH2NH2)3Zn2Ge2Se8: A new,templated one-dimensional ternary semiconductor stabilized by mixed organic cations

The novel, 1D semiconductor (H₂NC₄H₈NCH₂CH₂NH₂)(HNCH₂CH₂NH₂)₃Zn₂Ge₂Se₈ has been synthesized under solvothermal conditions using N-(2-aminoethyl)piperazine as solvent and templating agent at 200 °C. The material was characterized by single crystal and powder X-ray diffraction, IR and Raman spectroscopy and thermogravimetric analysis. The compound consists of 1D anionic [Zn₂Ge₂Se₈]⁴⁻ chains made of alternating edge-shared [ZnSe₄] and [GeSe₄] tetrahedra that charged balanced by one N-(2-aminoethyl)piperazinium and three piperazinium cations. The optical properties were investigated with solid state UV–Vis/near IR spectroscopy and the results show that the solid is a medium gap semiconductor with an absorption edge at 1.8 eV.     

Tetradentate Schiff-base ruthenium(III) complexes containing triphenylphosphine/arsine as coligands: study of physico-chemical,spectrometric, catalytic,and biocidal activities

A series of air-stable, low-spin Ru(III) octahedral complexes [RuX(EPh₃)L] (where X = Cl/Br; E = P/As; and L = dibasic tetradentate Schiff base derived by condensation of ethylenediamine with acetoacetanilide/acetoacetotoluidide/ethylacetoacetate in 1 : 2 molar ratio in ethanol) have been synthesized from RuX₃(EPh₃)₃ (where X = Cl/Br and E = P/As) with Schiff bases in 1 : 1 molar ratio in benzene for 6 h. These complexes were characterized by elemental analysis, spectral methods (Fourier transform infrared (FT-IR), UV-Vis, ¹H- and ¹³C-nuclear magnetic resonance (NMR) for the ligands, and electron paramagnetic resonance (EPR)), and are examined electrochemically. The complexes were efficient catalysts for oxidation of primary and secondary alcohols in their corresponding aldehydes and ketones in the presence of molecular oxygen. These complexes were also tested for their antibacterial and antifungal activities.     

Electrochemical studies of group III alkyl derivatives: II. Synthesis of adducts of trimethylindium and trimethylgallium

Electrolysis of methylmagnesium chloride or dimethylmagnesium in tetrahydrofuran (thf) with an indium anode yields the spectroscopically characterised adduct Me₃In · thf directly; the adducts Me₃In · L (L = NEt₃, PMe₃, PEt₃) are obtained by direct addition of excess L to Me₃In · thf.     

Synthesis of ternary and quaternary CuInxGa1−xSe2 (0 ≤ x ≤ 1) semiconductor nanocrystals

Semiconducting CuIn_xGa_1−xSe₂ nanocrystals (20–30 nm) have been synthesized over the whole composition range using a facile solution-based method. Depending on the synthesis conditions, the nanocrystals exhibit a cubic or spherical morphology with a narrow size distribution. The band gap increases with increasing Ga concentration and the values are close to those observed in the bulk.     

A study of arsenic(III) and arsenic(V) reduction and of arsine decomposition in hydride-generation atomic absorption spectrometry

The difference in behaviour of arsenic(III) and arsenic(V) in their conversion to arsine by reduction with sodium tetrahydroborate, and the role of the addition of oxygen and hydrogen to the carrier gas in the production of arsenic atoms are described.     

Ligating properties of tertiary phosphine/arsine sulphides or selenides. Part VII. Synthesis and characterisation of palladium(II) complexes with some mono- and ditertiary phosphine sulphides or selenides

Summary Palladium(II) halides react with triphenylphosphine sulphide or selenide, 1,1-methylenebis(diphenylphosphine sulphide or selenide) (MDPS or MDPSe), 1,3-trimethylene-bis-(diphenylphosphine selenide) (PDPSe) or tetramethyldiphosphine disulphide (TMDPS) forming complexes [PdBr₂ · 2L], [2PdBr₂ · 3L] (L=Ph₃PS or Ph₃PSe), [PdX₂ · L] (X=Cl, L =PDPSe; X=Br, L=MDPS or MDPSe; X=Cl or Br, L=TMDPS) and [3PdBr₂ · 2TMDPS]. Characterisation and stereochemical assignments have been made through elemental analyses, i.r., far i.r. and electronic spectra, magnetic susceptibility and molar conductance data and tga studies. Bidentate ligand complexes have higher thermal stability than the monodentate ligand complexes. Chelation or bridging modes of the bidentate ligands have been demonstrated.     

Infrared matrix isolation spectroscopy of trimethylgallium,trimethylaluminium and triethylaluminium

Infrared spectra (4000-300 cm⁻¹) of the title aluminium trialkyls are reported both for the dimers and the monomers. Spectra of monomeric (CH₃)₃Al and (CH₃CH₂)₃Al, obtained by dissociation of the dimers at 300 and 80°C, respectively, are reported for the first time. The spectra of matrix isolated (CH₃)₃Al and (CH₃)₃Ga are discussed in terms of a planar skeleton with rotational tunnelling of the methyl groups, i.e. symmetry group G₃₂₄ or effective point symmetry D_3h. Monomeric (CH₃CH₂)₃Al has been treated in a similar manner although the assignments of the ethyl modes are more complex. The interpretation of the spectra is supplemented with normal coordinate calculations. Controlled dimerization of matrix isolated monomeric (CH₃)₃Al by annealing indicates a mechanism proceeding via a single-bridged intermediate.     

Synthesis and structure of dimeric Rh-bis(tertiary phosphine) complexes,exceptionally useful synthetic precursors

Removal of the MeOH and hydrogen from the known cis,trans,cis-Rh^III-dihydrido complexes 〚Rh(H)₂(PR₃)₂(MeOH)₂〛PF₆ (R = Ph, p-tolyl) results in formation of the dimeric species 〚Rh₂(PR₃)₄〛〚PF₆〛₂; X-ray analysis shows the complexes to be 〚(Ph₃P)Rh(μ-PhPPh₂)〛₂〚PF₆〛₂ (and the p-tolyl analogue) containing bridged η⁶-arene moieties, while ¹H and ¹³C NMR data in CD₂Cl₂ provide evidence for η⁴-coordination of the arene within the dimer. In more strongly coordinating solvents, formation of cis-〚Rh(PR₃)₂(solvent)₂〛PF₆ is observed, while formation of 〚(PR₃)₂Rh(η⁶-toluene)〛PF₆ is evident in toluene solution, and this exists in equilibrium with the bis(solvent) species in the presence, for example, of acetone or MeOH. At ambient conditions, none of the arene-containing complexes effected catalytic H₂-hydrogenation of toluene.