The Autoxidation of Triaryl Trithioarsenites, (ArS)3As: Evidence for Binding and Activation of Triplet Dioxygen by Arsenic(III)

Triaryl trithioarsenites, (ArS)₃As, are oxidized by air to As ₂ O ₃ and ArSSAr. In two cases the parent “thiol” (pyrid-2-thione and 1-hydroxypyrid-2-thione) is coproduced. The oxidation, in nonprotic solvents, is favored by electron-withdrawing groups at the para position of the phenyl group. The products obtained in nonprotic solvents were rationalized by assuming that the binding of the triplet dioxygen to arsenic(III) gives a triplet diradical, (ArS) ₃ A?─O─?, or an arsenadioxirane, (ArS) ₃ As(O ₂ ), intermediate, which decomposes after nucleophilic attack by another (ArS) ₃ As molecule. In protic solvents a zwitterion, (ArS) ₃ As⁺─O─O^?, and in the presence of moisture a hydroperoxy arsenic(V) compound, (ArS)₃As(OH)─O─OH, may be intermediates in the air oxidation of some aromatic trithioarsenites. These data tend to indicate that arsenic(III) bound to suitable groups can directly bind dioxygen, a property which may have implications in chemotherapy and carcinogenesis.     

On the Reaction of Triaryl Trithioarsenites, (ArS)3As,with Iodine

Iodine in dry nonprotic solvents oxidizes triaryl trithioarsenites, (ArS)₃As, to As(III) iodide, AsI₃, and disulfides, ArSSAr. The reaction most likely involves arylsulfenyl iodide, ArSI, as an intermediate. With triphenyl and tris(4-chlorophenyl) trithioarsenites, AsI₃ is prepared in very good yields. When the disulfide, which is produced, has MeCONH─ or ─NH─CMe₂─OH groups, then it acts as a Lewis base towards AsI₃ forming complexes with stoichiometry 2AsI₃·3ArSSAr. Probable coordination modes of the AsI₃ are discussed.     

On the Reaction of Dithioarsonites,L‐As(SPh)2 (L = Ar,R), with Octasulfur in the Presence of Triethylamine as an Activator. The Crystal Structure of the Sesquisulfide (2‐O2N‐C6H4‐As)2S3

Octasulfur (elemental sulfur) does not react at room temperature with a variety of As^III compounds of the type Ar‐As(SPh)₂ and R‐As(SPh)₂. However, in the presence of catalytic amounts of triethylamine, which probably acts as an activator of octasulfur, reactions do take place. The products isolated from the aromatic dithioarsonites are not the expected Ar‐As(S)(SPh)₂ but the sulfide, cyclo‐(PhAsS)₄, and the sesquisulfides, (ArAs)₂S₃, which are the same with those obtained by reduction of arylarsonic acids with hydrogen sulfide. The action of S₈/Et₃N on aliphatic dithioarsonites did not give any As^V products but gave mixtures of non‐separable oligomeric (RAsS)_x. Probable mechanistic routes for these reactions are proposed. The known cyclo‐(PhAsS)₄ and (PhAs)₂S₃ and the new (2‐O₂N‐C₆H₄‐As)₂S₃ have been structurally characterized: (2‐O₂N‐C₆H₄‐As)₂S₃, monoclinic, C2/c, a = 13.564(9)Å, b = 7.982(6)Å, c = 16.67(1)Å, β = 117.63(2)°, V = 1599(2)ų, Z = 4, wR2 0.0640. The 1, 4‐diarsa‐2, 3, 5‐trithiacyclopentane ring is puckered and the two As^III atoms are pseudo tetrahedral.     

Enhanced Anticancer Cells Effects of Optimized Suspension Stable As2O3‐Loaded Poly(lactic‐co‐glycolic acid) Nanocapsules

This study is to prepare a nanosuspension based on poly(lactic‐co‐glycolic acid) (PLGA) for delivery, controlled release and enhanced anti‐solid tumor effects of As₂O₃. As₂O₃‐loaded PLGA nanocapsules (As₂O₃‐PLGA NCs) were prepared by double emulsion‐solvent evaporation method and were optimized by univariate analysis in combination with orthogonal experimental according to several factors. The optimized As₂O₃‐PLGA NCs presented suitable physical stability, favorable size of (200.2±10.6) nm (PDI=0.117±0.008), spherical shape, and high encapsulation efficiency (92.48%±2.14%). The in vitro suspension stability of the NCs was excellent. The release of As₂O₃ from the NCs showed pH responsive release characteristics. The NCs can be efficiently taken up by SMMC‐7721 cell and showed excellent antitumor efficacy against SMMC‐7721 cell line. Then, As₂O₃‐PLGA NCs could be considered as a promising formulation for the pH dependent release of As₂O₃ in cancer cells and enhance the anti‐solid tumor effects of As₂O₃.     

The Reaction of Bunsen's Cacodyl Disulfide,Me2As(S)‐S‐AsMe2, with Iodine: Preparation and Properties of Dimethylarsinosulfenyl Iodide,Me2As‐S‐I

Bunsen's cacodyl disulfide, Me₂As(S)‐S‐AsMe₂ ( 1 ), reacted with iodine giving the novel dimethylarsinosulfenyl iodide, Me₂As‐S‐I ( 3 ) although theoretical calculations indicated that the As^V compound Me₂As(S)‐I ( 4 ) was more stable in the gas phase. The oily product was stable neat and as a solution in CDCl₃ at +4 °C and –20 °C for at least 15 d. Light, H₂O, H₂O₂, and Zn dust, but not NaI or Ag, decomposed it. Compound 3 did not interact with Ph₃N, with Ph₂NH and PhNH₂ it interacted but not reacted. 3 was decomposed by piperidine, with pyridine and 4‐dimethylaminopyridine it interacted and produced Me₂As‐SS‐AsMe₂ ( 2 ) and I₂ that formed charge transfer complexes Base · I₂, whereas Et₃N decomposed 3 , and 3Et₃N · 2I₂ was isolated. 3 was desulfurized by Ph₃P and (Me₂N)₃P completely, and by (PhO)₃P and (PhS)₃P partially. The reactions of 3 with (Me₂N)₃P, (PhS)₃P, and (EtO)₃P were complicated. From the As^III nucleophiles, only Ph₃As was bound, while (PhS)₃As reacted slowly in a complicated manner with 3 . No interaction of 3 with MeOH or PhOH was observed but NaOH, Ag₂O, and PhONa decomposed it. Thiophenol produced traces of Me₂As‐SPh ( 10 ) and sodium thiophenolate attacked mainly at As^III of 3 . Thus, externally stabilized sulfenium ions of the type Me₂As‐S‐Nu⁺I^– were not obtained.     

An investigation of polyhedral deformation in two mixed‐metal diarsenates: SrZnAs2O7 and BaCuAs2O7

Two isostructural diarsenates, SrZnAs₂O₇ (strontium zinc diarsenate), (I), and BaCuAs₂O₇ [barium copper(II) diarsenate], (II), have been synthesized under hydrothermal conditions and characterized by single‐crystal X‐ray diffraction. The three‐dimensional open‐framework crystal structure consists of corner‐sharing M2O₅ (M2 = Zn or Cu) square pyramids and diarsenate (As₂O₇) groups. Each As₂O₇ group shares its five corners with five different M2O₅ square pyramids. The resulting framework delimits two types of tunnels aligned parallel to the [010] and [100] directions where the large divalent nine‐coordinated M1 (M1 = Sr or Ba) cations are located. The geometrical characteristics of the M1O₉, M2O₅ and As₂O₇ groups of known isostructural diarsenates, adopting the general formula M1^IIM2^IIAs₂O₇ (M1^II = Sr, Ba, Pb; M2^II = Mg, Co, Cu, Zn) and crystallizing in the space group P2₁/n, are presented and discussed.     

Syntheses and Crystal Structures of Four New Ammoniates with Heptaarsenide (As$\rm{_{7}^{3-}}$) Anions

The syntheses and X‐ray single‐crystal low‐temperature structures of the four new ammoniates [Li(NH₃)₄]₃As₇?NH₃ ( 1 ), [Rb(18‐crown‐6)]₃As₇?8 NH₃ ( 2 ), Cs₃As₇?6 NH₃ ( 3 ), and (Ph₄P)₂CsAs₇?5 NH₃ ( 4 ) are reported. The compounds were obtained by either direct reduction of As with Li/Cs in liquid NH₃, solvation of Cs₄As₆/Rb₄As₆ in liquid NH₃, or by extraction of solid Cs₃As₇. While compound 1 contains isolated As polyanions, As? M contacts (M=Na?Cs) lead to neutral [Rb(18‐crown‐6)]₃As₇ units in 2 , a three‐dimensional, extended network in 3 , and one‐dimensional, infinite [CsAs₇]^2? chains in 4 , respectively.     

Synthesis,Structure and Property of a Dawson-type Arsenomolybdate with an Appended AsIII Cap

An inorganic–organic hybrid compound, (H₂bpy)₃[As^IIIAs₂ ^VMo₁₅ ^VIMo₃ ^VO₆₂]·3H₂O (bpy: 4,4′-bipyridine) (1) has been synthesized under hydrothermal conditions and characterized by elemental analysis, X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction, IR spectrum, UV–Vis spectrum, thermogravimetric analysis and single-crystal X-ray diffraction. The crystallographic analysis reveals that compound 1 is composed of a Wells–Dawson polyoxoanion [As₂ ^VMo₁₅ ^VIMo₃ ^VO₆₂]^9? with the mixed valence of Mo^V,VI, which acts as a tetradentate ligand coordinating with the As^III cation to form the mixed valence As^III,V containing arsenomolybdate with the single cap structure in a chelate coordination mode. In the solid state, compound 1 shows a 3D supramolecular structure through hydrogen-bonding interactions (C–H···O, N–H···O, N–H···N). In addition, compound 1 exhibits reversible multi-electron redox processes and effective electrocatalytic activities towards the reduction of H₂O₂, NaNO₂ and KBrO₃. Moreover, compound 1 is used as a reducing agent of the graphene oxide to prepare graphene by a green chemistry type one-step synthesis method, which is characterized by XPS, Raman spectroscopy, PXRD, IR, scanning electron microscopy and transmission electron microscopy.     

Die Chlorooxoarsenate(III) (PPh4)2[As4O2Cl10] · 2 CH3CN und (PPh4)2[As2OCl6] · 3 CH3CN

The Chlorooxoarsenates(III) (PPh₄)₂[As₄O₂Cl₁₀] · 2 CH₃CN and (PPh₄)₂[As₂OCl₆] · 3 CH₃CN (PPh₄)₂[As₂Cl₈] can be prepared from As₂O₃, SOCl₂ and PPh₄Cl in acetonitrile. Its oxidation with chlorine yields PPh₄[AsCl₆]. This was also obtained directly from arsenic, chlorine and PPh₄Cl, (PPh₄)₂[As₄O₂Cl₁₀] · 2 CH₃CN being a side product; the latter was obtained with high yield from AsCl₃, As₂O₃ and PPh₄Cl in acetonitrile. By addition of PPh₄Cl it was converted to (PPh₄)₂[As₂OCl₆] · 3 CH₃CN. According to their X-ray crystal structure analyses, both crystallize in the triclinic space group P 1. The [As₄O₂Cl₁₀]^2– ion can be regarded as a centrosymmetric association product of two Cl₂AsOAsCl₂ molecules and two Cl^– ions, each Cl^– ion being coordinated with all four As atoms. In the [As₂OCl₆]^2– ion the As atoms are linked via the O atom and two Cl atoms.     

Organoantimony(III)‐Containing Tungstoarsenates(III): From Controlled Assembly to Biological Activity

A family of three sandwich‐type, phenylantimony(III)‐containing tungstoarsenates(III), [(PhSb^III){Na(H₂O)}As^III₂W₁₉O₆₇(H₂O)]^11? ( 1 ), [(PhSb^III)₂As^III₂W₁₉O₆₇(H₂O)]^10? ( 2 ), and [(PhSb^III)₃(B‐α‐As^IIIW₉O₃₃)₂]^12? ( 3 ), have been synthesized by one‐pot procedures and isolated as hydrated alkali metal salts, Cs₃K_3.5Na_4.5[(PhSb^III){Na(H₂O)}As^III₂W₁₉O₆₇(H₂O)]?41H₂O ( CsKNa ‐ 1 ), Cs_4.5K_5.5[(PhSb^III)₂As^III₂W₁₉O₆₇(H₂O)]?35H₂O ( CsK‐2 ), and Cs_4.5Na_7.5[(PhSb^III)₃(B‐α‐As^IIIW₉O₃₃)₂]?42H₂O ( CsNa ‐ 3 ). The number of incorporated {PhSb^III} units could be selectively tuned from one to three by careful control of the reaction parameters. The three compounds were characterized in the solid state by single‐crystal XRD, IR spectroscopy, and thermogravimetric analysis. The aqueous solution stability of sandwich polyanions 1 – 3 was also studied by multinuclear (¹H, ¹³C, ¹⁸³W) NMR spectroscopy. Effective inhibitory activity against six different kinds of bacteria was identified for all three polyanions, for which the activity increased with the number of incorporated {PhSb^III} groups.     

Solar Light Photocatalytic Degradation of Malachite Green by Hydrothermally Synthesized Strontium Arsenate Nanomaterial through Response Surface Methodology

Nanostructured Sr₂As₂O₇ samples were synthesized by hydrothermal crystal growth reactions between Sr(NO₃)₂ and As₂O₃ with different stoichiometric Sr:As molar ratios as 1:1 (S₁), 1:2 (S₂), and 2:1 (S₃). The synthesized nanomaterials were characterized by powder X‐ray diffraction (PXRD) technique and fourier‐transform infrared (FT‐IR) spectroscopy. Rietveld analysis showed that the obtained materials were crystallized well in the monoclinic crystal structure with the space group P2₁. The morphologies of the synthesized materials were studied by field emission scanning electron microscopy (FESEM) technique. TEM images verified formation of the particles with nanometer size. Ultraviolet‐visible spectra analysis showed that the synthesized Sr₂As₂O₇ nanomaterials had strong light absorption in the ultraviolet light region. Photocatalytic performance of the synthesized nanomaterials was also investigated for the degradation of pollutant Malachite Green (4‐{[4‐(dimethylamino)phenyl](phenyl)methylidene}‐N′N‐dimethylcyclohexa‐25‐dien‐1‐iminium chloride) (MG) in aqueous solution under solar light condition. The optimal conditions were obtained by design expert software for S₁. It was found that the optimum condition was 0.14 mL H₂O₂, 20 mg catalyst, and 33 min time. The volume and concentration of the as prepared MG solution were 70 mL and 100 ppm, respectively, for obtaining the optimum conditions. The degradation yield in the optimized conditions was 97 % for S₁.     

Modular Molecules: Site‐Selective Metal Substitution,Photoreduction, and Chirality in Polyoxometalate Hybrids

The first members of a promising new family of hybrid amino acid–polyoxometalates have emerged from a search for modular functional molecules. Incorporation of glycine (Gly) or norleucine (Nle) ligands into an yttrium‐tungstoarsenate structural backbone, followed by crystallization with p‐methylbenzylammonium (p‐MeBzNH₃⁺) cations, affords (p‐MeBzNH₃)₆K₂(GlyH)[As^III₄(Y^IIIW^VI₃)W^VI₄₄Y^III₄O₁₅₉(Gly)₈‐ (H₂O)₁₄] ? 47 H₂O ( 1 ) and enantiomorphs (p‐MeBzNH₃)₁₅(NleH)₃ [As^III₄(Mo^V₂Mo^VI₂)W^VI₄₄Y^III₄O₁₆₀(Nle)₉(H₂O)₁₁][As^III₄(Mo^VI₂W^VI₂)‐ W^VI₄₄Y^III₄O₁₆₀(Nle)₉(H₂O)₁₁] (generically designated 2 : L ‐Nle, 2 a ; D ‐Nle, 2 b ). An intensive structural, spectroscopic, electrochemical, magnetochemical and theoretical investigation has allowed the elucidation of site‐selective metal substitution and photoreduction of the tetranuclear core of the hybrid polyanions. In the solid state, markedly different crystal packing is evident for the compounds, which indicates the role of noncovalent interactions involving the amino acid ligands. In solution, mass spectrometric and small‐angle X‐ray scattering studies confirm maintenance of the structure of the polyanions of 2 , while circular dichroism demonstrates that the chirality is also maintained. The combination of all of these features in a single modular family emphasizes the potential of such hybrid polyoxometalates to provide nanoscale molecular materials with tunable properties.     

Group IVB organometallic sulphides : VIII. Reaction of triorgano-germanium and -tin aryl sulphides with oxidants. some reactions of triorgano-germanium and -tin aryl o-sulphinates with sulphur halides

R₃SnSAr are oxidised by H₂O₂, 2,4,4,6-tetrabromocyclohexa-2,5-dienone and NaIO₄ (in 1 : 1 ratio) to disulphides, ArSSAr. With NaIO₄ as the oxidant, Ph₃SnSAr, gives a complex triphenyltin periodate; however, with the other two oxidants, (Ph₃Sn)₂O is produced. Ph₃GeSAr was oxidised by NaIO₄ to (Ph₃Ge)₂O and ArSSAr.Triorgano-germanium and -tin O-sulphinates, R₃MOSOAr react with arenesulphenyl chlorides, ArSCl, giving thiosulphonates, ArSS(O₂)Ar, and with sulphur dichloride, producing di(sulphonyl) sulphides ArS(O₂)SS(O₂)Ar. Triorgano-germanium p-toluene sulphonate readily formed by oxidation of the O-sulphinate derivative, does not react with arenesulphenyl chlorides.     

Electrochemical Biosensor for the Detection of Interaction Between Arsenic Trioxide and DNA Based on Guanine Signal

The interaction of arsenic trioxide (As₂O₃) with calf thymus double‐stranded DNA (dsDNA), calf thymus single‐stranded DNA (ssDNA) and also 17‐mer short oligonucleotide (Probe A) was studied electrochemically by using differential pulse voltammetry (DPV) with carbon paste electrode (CPE) at the surface and also in solution. Potentiometric stripping analysis (PSA) was employed to monitor the interaction of As₂O₃ with dsDNA in solution phase by using a renewable pencil graphite electrode (PGE). The changes in the experimental parameters such as the concentration of As₂O₃, and the accumulation time of As₂O₃ were studied by using DPV; in addition, the reproducibility data for the interaction between DNA and As₂O₃ was determined by using both electrochemical techniques. After the interaction of As₂O₃ with dsDNA, the DPV signal of guanine was found to be decreasing when the accumulation time and the concentration of As₂O₃ were increased. Similar DPV results were also found with ssDNA and oligonucleotide. PSA results observed at a low DNA concentration such as 1 ppm and a different working electrode such as PGE showed that there could be damage to guanine bases. The partition coefficients of As₂O₃ after interaction with dsDNA and ssDNA in solution by using CPE were calculated. Similarly, the partition coefficients (PC) of As₂O₃ after interaction with dsDNA in solution was also calculated by PSA at PGE. The features of this proposed method for the detection of DNA damage by As₂O₃ are discussed and compared with those methods previously reported for the other type of DNA targeted agents in the literature.     

Two New Polyoxovanadate‐supported Transition Metal Complexes: [Zn(en)2][Zn(en)2(H2O)2][{Zn(en)(enMe)}As6V15O42(H2O)]·4H2O and [Zn2(enMe)2(en)3][{Zn(enMe)2}As6V15O42(H2O)]·4H2O

Two novel As‐V‐O cluster supported transition metal complexes, [Zn(en)₂][Zn(en)₂(H₂O)₂][{Zn(en)(enMe)}As₆V₁₅O₄₂(H₂O)]·4H₂O ( 1 ) and [Zn₂(enMe)₂(en)₃][{Zn(enMe)₂}As₆V₁₅O₄₂(H₂O)]·4H₂O ( 2 ), have been hydrothermally synthesized. The single X‐ray diffraction studies reveal that both compounds consist of discrete noncentral polyoxoanions [{Zn(en)(enMe)}As₆V₁₅O₄₂(H₂O)]^4? or [{Zn(enMe)₂}As₆V₁₅O₄₂(H₂O)]^4? cocrystallized with respective zinc coordination complexes. Interestingly, compounds 1 and 2 exhibit the first two polyoxovanadates containing As₈V₁₅O₄₂‐(H₂O)]^6? cluster decorated by only one transition metal complex. Crystal data: 1 , monoclinic, P2₁/n, a = 14.9037(4) Å, b = 18.1243(5) Å, c = 27.6103(7) Å, β = 105.376(6)°, Z = 4; 2 monoclinic, P2₁/n, a = 14.9786(7) Å, b = 33.0534(16) Å, c = 14.9811(5) Å, Z = 4.     

Zur Kenntnis von Ba2As6O11

Concerning Ba₂As₆O₁₁ Ba₂As₆O₁₁ was prepared by hydrothermal reaction of BaO with As₂O₃ at a temperature of 200°C. An X-ray structural analysis demonstrated that the phase contains highly condensed polyarsenate(III) anions (As₆O₁₁^4?)_n. A zweier double chain structure was observed for the anion, in which the individual chains are bridged to one another by two Ψ-AsO₃ tetrahedra, so that As₁₀O₁₀ rings are formed. The double chains are linked into “double sheets”, perpendicular to the b-axis, through relatively strong secondary O … As bonds with an average length of 2.68 Å.     

Synthese,Kristallstrukturen und Magnetismus von (Hg6As4)[MoCl6]Cl, (Hg6As4)[TiCl6]Cl und (Hg6As4)[TiBr6]Br

Polycationic Hg–As Frameworks with Trapped Anions. II Synthesis, Crystal Structure, and Magnetism of (Hg₆As₄)[MoCl₆]Cl, (Hg₆As₄)[TiCl₆]Cl, and (Hg₆As₄)[TiBr₆]Br (Hg₆As₄)[MoCl₆]Cl is obtained by reaction of Hg₂Cl₂, Hg, As, and MoCl₄ in closed, evacuated glass ampoules in a temperature gradient 450 → 400 °C in form of dark red cubelike crystals. (Hg₆As₄)[TiCl₆]Cl and (Hg₆As₄)[TiBr₆]Br are also formed in closed, evacuated ampoules from Hg₂X₂ (X = Cl, Br), Hg, As, and Ti metal at 275 °C and 245 °C in form of dark green and black crystals, respectively. All three compounds are air and light sensitive. They crystallize isotypically (cubic, Pa 3, a = 1207.8(4) pm for (Hg₆As₄)[MoCl₆]Cl, a = 1209.4(3) pm for (Hg₆As₄)[TiCl₆]Cl, a = 1230.9(3) pm for (Hg₆As₄)[TiBr₆]Br, Z = 4). The structures consist of a three‐dimensionally connected Hg–As framework which is made up of As₂ groups (As–As distance averaged 242 pm) each connected via six Hg atoms to six neighbouring As₂ groups. There are two cavities of different size in the polycationic framework. The bigger cavity is filled with [MoCl₆]^3–, [TiCl₆]^3–, and [TiBr₆]^3– ions of nearly ideal octahedral shape, the smaller cavity with discrete halide ions. The magnetic properties of the two Ti containing compounds are in accordance with a d¹ paramagnetism. The temperature dependence and the magnitude of the magnetic moment can be interpreted with consideration of the spin‐orbit coupling. The so far known representatives of this structure type can be characterised by the ionic formula (Hg₆Y₄)⁴⁺[MX₆]^3–X^– (Y = As, Sb; M = Sb³⁺, Bi³⁺, Mo³⁺, Ti³⁺; X = Cl, Br).     

Sm2As4O9: Ein ungewöhnliches Samarium(III)‐Oxoarsenat(III) gemäß Sm4[As2O5]2[As4O8]

Sm₂As₄O₉: An Unusual Samarium(III) Oxoarsenate(III) According to Sm₄[As₂O₅]₂[As₄O₈] Pale yellow single crystals of the new samarium(III) oxoarsenate(III) with the composition Sm₄As₈O₁₈ were obtained by a typical solid‐state reaction between Sm₂O₃ and As₂O₃ using CsCl and SmCl₃ as fluxing agents. The compound crystallizes in the triclinic crystal system with the space group (No. 2, Z = 2; a = 681.12(5), b = 757.59(6), c = 953.97(8) pm, α = 96.623(7), β = 103.751(7), γ = 104.400(7)°). The crystal structure of samarium(III) oxoarsenate(III) with the formula type Sm₄[As₂O₅]₂[As₄O₈] (≡ 2 × Sm₂As₄O₉) contains two crystallographically different Sm³⁺ cations, where (Sm1)³⁺ is coordinated by eight, but (Sm2)³⁺ by nine oxygen atoms. Two different discrete oxoarsenate(III) anions are present in the crystal structure, namely [As₂O₅]^4? and [As₄O₈]^4?. The [As₂O₅]^4? anion is built up of two Ψ¹‐tetrahedra [AsO₃]^3? with a common corner, whereas the [As₄O₈]^4? anion consists of four Ψ¹‐tetrahedra with ring‐shaped vertex‐connected [AsO₃]^3? pyramids. Thus at all four crystallographically different As³⁺ cations stereochemically active non‐binding electron pairs (“lone pairs”) are observed. These “lone pairs” direct towards the center of empty channels running parallel to [010] in the overall structure, where these “empty channels” being formed by the linkage of layers with the ecliptically conformed [As₂O₅]^4? anions and the stair‐like shaped [As₄O₈]^4? rings via common oxygen atoms (O1 – O6, O8 and O9). The oxygen‐atom type O7, however, belongs only to the cyclo‐[As₄O₈]^4? unit as one of the two different corner‐sharing oxygen atoms.     

Mehrkernige Eisen/Tantal‐ und Tantal‐Komplexe mit Asn‐Liganden

Polynuclear Iron/Tantalum and Tantalum Complexes with As_n Ligands Starting with [Cp@Ta(CO)₄] ( 1 ) (Cp@ = C₅H₃^tBu₂‐1,3) and As₄ or (^tBuAs)₄ ( 2 ) its thermolysis at 190 °C in decalin gives [{Cp@Ta}₂(μ‐η⁴ : η⁴‐As₈)] ( 3 ), which is also formed according to equation (2) in addition to [{Cp@Ta}₃As₆] ( 5 ). The reaction of 1 or [{Cp*(OC)₂Fe}₂] ( 6 ) with 3 affords 5 or [{Cp*Fe}{Cp@Ta}As₅] ( 8 ) demonstrating the use of 3 as As_n source. 8 can also be synthesized from 1 and [Cp*Fe(η⁵‐As₅)] ( 7 ) for which the cothermolysis of 2 and 6 gives a better yield.     

Exploring the intrinsic polar [4 + 2+] cycloaddition reactivity of gaseous carbosulfonium and carboxonium ions

Gas‐phase reactions of model carbosulfonium ions (CH₃‐S⁺ = CH_2; CH₃CH₂‐S⁺ = CH₂ and Ph‐S⁺ = CH₂) and an O‐analogue carboxonium ion (CH₃‐O⁺ = CH₂) with acyclic (isoprene, 1,3‐butadiene, methyl vinyl ketone) and cyclic (1,3‐cyclohexadiene, thiophene, furan) conjugated dienes were systematically investigated by pentaquadrupole mass spectrometry. As corroborated by B3LYP/6‐311 G(d,p) calculations, the carbosulfonium ions first react at large extents with the dienes forming adducts via simple addition. The nascent adducts, depending on their stability and internal energy, react further via two competitive channels: (1) in reactions with acyclic dienes via cyclization that yields formally [4 + 2⁺] cycloadducts, or (2) in reactions with the cyclic dienes via dissociation by HSR loss that yields methylenation (net CH⁺ transfer) products. In great contrast to its S‐analogues, CH₃‐O⁺ = CH₂ (as well as C₂H₅‐O⁺ = CH₂ and Ph‐O⁺ = CH₂ in reactions with isoprene) forms little or no adduct and proton transfer is the dominant reaction channel. Isomerization to more acidic protonated aldehydes in the course of reaction seems to be the most plausible cause of the contrasting reactivity of carboxonium ions. The CH₂ = CH‐O⁺ = CH₂ ion forms an abundant [4 + 2⁺] cycloadduct with isoprene, but similar to the behavior of such α,β‐unsaturated carboxonium ions in solution, seems to occur across the C = C bond. Copyright © 2012 John Wiley & Sons, Ltd.