As-C Bond Research Articles

Transformation of p-arsanilic acid by dissolved Mn(III) and enhanced arsenic removal: Mechanism, toxicity and performance in complicated water matrices

Dissolved Mn(III), as a potent one-electron transfer oxidant, is ubiquitous in natural waters and sediments and actively involved in the transformation of organics in biogeochemical processes and water treatment. However, the important role of Mn(III) has long been overlooked because of its short life. This study was the first to investigate the performance of Mn(III) in organoarsenic transformation and to highlight the environmental implications. Both homogeneous and heterogeneous Mn(III)-based systems were effective to remove p-arsanilic acid (p-ASA, 15 μM) with degradation efficiency approaching 40.4 %–98.3 %. Two degradation pathways of p-ASA were proposed, in which As-C bond and amino group were vulnerable sites to Mn(III) attack, leading to the formation of more toxic arsenate (As(V)) and nitarsone. Through transforming organoarsenic to inorganic arsenic species, the removal efficiency of total arsenic and dissolved organics were enhanced to 65.1 %–95.5 % and 16.6 %–36.6 %, respectively, by post-treatment of coagulation or adsorption, accompanied with significant reduction of cytotoxicity and environmental risks. Particularly, polymeric ferric sulfate and granular activated alumina showed superior performance in the total As removal. Moreover, oxidation efficiency of Mn(III) was hardly affected by common cations and anions (e.g., Ca2+, Mg2+, NH4+, NO3ˉ, SO4ˉ), halide ions (e.g., Clˉ, Brˉ) and natural organic matter, showing high robustness for organoarsenic removal under complicated water matrices. Overall, this study shed light on the significance of Mn(III) to the fate of organoarsenics in manganese-rich environments, and demonstrated the promising potential of Mn(III)-based strategies to achieve targeted decontamination in water/wastewater purification.

Synergistic redox and adsorption for enhanced Roxarsone removal: Heterogeneous Fenton-Like reaction with a novel composite of nanoscale zero-valent iron supported on γ-aluminum oxide

Roxarsone (ROX), a livestock growth enhancer, poses environmental and health hazards due to its remarkable stability, making traditional degradation methods ineffective. To tackle this issue, a novel Fenton-like composite, composed of nanoscale zero-valent iron supported on γ-aluminum oxide (nZVI/γ-Al2O3), was synthesized to boost ROX degradation. Results demonstrated nearly complete mineralization of the ROX organic matrix within just 180 min, facilitated by the Lewis acidity sites of γ-Al2O3. Significantly, this composite exhibited selective adsorption of released AsO43− ions on its surface, forming FeAsO4 and Fe-As-Al complexes. It also established an internal redox cycle involving Fe(0), Fe(II), and Fe(III), ensuring a continuous and efficient generation of primary reactive oxygen species (·OH and O2·−). Thus, a simultaneous redox process occurred on the composite surface can be attributed to the synergy of the reducibility of nZVI and the oxidation catalyzed by ·OH and O2·−. Initially, the nitro group of ROX was reduced by nZVI, forming more hydrophilic o-aminophenol, favoring subsequent oxidation and mineralization. Simultaneously, the As-C bonds in ROX were oxidized, yielding AsO43−, which was subsequently adsorbed over extended reaction times. This innovative approach offers a potential solution for treating wastewater contaminated with metalloid-organic composite pollutants, addressing the environmental and health concerns associated with ROX residues.

Electrochemical Performance of Graphene Oxide/Black Arsenic Phosphorus/Carbon Nanotubes as Anode Material for LIBs.

As a new two-dimensional material, black arsenic phosphorus (B-AsP) has emerged as a promising electrode for lithium-ion batteries (LIBs) due to its large theoretical capacity and ability to absorb large amounts of Li atoms. However, the poor electronic conductivity and large volume expansion during the lithiation/delithiation process have largely impeded the development of B-AsP electrodes. In this study, graphene oxide (GO)/B-AsP/carbon nanotubes (CNTs) with remarkable lithium-storage property were fabricated via CVD and ultrasound-assisted method. The electrochemical behavior of the GO/B-AsP/CNTs was investigated as an anode in lithium-ion batteries. From the results, as a new-type anode for LIBs, GO/B-AsP/CNTs composite demonstrated a stable capacity of 1286 and 339 mA h g−1 at the current density of 0.1 and 1 A g−1, respectively. The capacity of GO/B-AsP/CNTs was 693 mA h g−1 after 50 cycles, resulting in capacity retention of almost 86%. In addition, the stable P-C and As-C bonds were formed between B-AsP, GO, and CNTs. Thus, volume expansion of B-AsP was alleviated and the capacity was increased due to the confining effect of GO and CNTs.

Degradation of p-arsanilic acid by pre-magnetized Fe0/persulfate system: Kinetics, mechanism, degradation pathways and DBPs formation during subsequent chlorination

Pre-magnetized Fe0/persulfate (pre-Fe0/PS) process was innovatively employed for controlling the pollution of p-arsanilic acid (p-ASA). This process showed favorable removal performance, achieving almost complete elimination of 10 mg/L p-ASA within 30 min at the reaction conditions of 0.2 g/L pre-Fe0 and 1 mM PS. The increase of PS concentration and pre-Fe0 dosage was conducive to the degradation. The coexistence of Cl−, NO3− and SO42− accelerated the removal, however the presence of HCO3− and HA presented the opposite trend. The p-ASA degradation decelerated gradually with increasing pH from 5 to 9. Its removal was caused by the attack of reactive oxygen species (i.e., SO4−, OH, O2−), which could be continuously formed via the Fe2+/Fe3+ cycle in solution and on pre-Fe0 surface. In pre-Fe0/PS system, SO4− in solution, surface-bound SO4−, OH, OH in solution, O2− in solution and Fe(IV) contributed to the p-ASA degradation. A plausible transformation route related to the break of C-N and As-C bonds, the substitution of OH group was put forward. More importantly, the released inorganic arsenic during p-ASA decomposition could be effectively controlled through multiple functions including the precipitation, co-precipitation and sorption, which was well confirmed by XPS, FTIR and XRD analysis. Pre-Fe0/PS and Fe0/PS pretreatments both reduced the generation of C-DBPs except for chloral hydrate, while increased the formation of N-DBPs except for trichloroacetamide.

Trapping AsPh3 via reaction with NiS/γ-Al2O3 in the presence of H2: Reaction mechanism and kinetics

Removal of As from petroleum feedstocks is an important process which can be realized using As trapping mass containing supported nickel sulfide. In order to understand the mechanism of the trapping we studied the reaction of AsPh3 with NiS/γ-Al2O3 in the presence of H2 in a batch reactor in toluene solution at 230 °C. This reaction results in formation of NiAs, benzene and H2S. Also, the intermediate species, thiophenol and diphenylsulfide, were observed. Despite formation of NiAs layer in the course of reaction, the rate of AsPh3 decomposition is not affected by the solid state diffusion up to ∼ 50 % of nickel conversion. The rate determining step in these conditions appears to be the hydrogenolysis of As-C bonds. It was found that the reaction order changes in the course of reaction from zero to one. This trend is described by a kinetic model assuming adsorption of AsPh3 molecules followed by decomposition.

C-As Bond Formation Reactions for the Preparation of Organoarsenic(III) Compounds.

Potential widespread applications of organoarsenic chemistry have been limited by the inherent lack of safe and effective As-C bond formation reactions. Several alternative reagents and methods have been developed in the last few decades to address the hazards and drawbacks associated with traditional arsenic synthetic strategies. Herein, this minireview summarizes the advances made in nucleophilic, electrophilic, radical and metal-mediated As(III)-C bond formations while specifically highlighting the behavior of arsenic synthons with various well-established reagents (eg. Grignard reagents, organolithium compounds, organometallic reagents, radical initiators and Lewis/Brønsted bases). Avenues for asymmetric synthesis are also discussed, as are recent advances in organoarsenic chemistry suggesting that arsines exhibit novel reactivities independent from that of other relatively more well explored Group V cogeners.

Simultaneous removal of para-arsanilic acid and the released inorganic arsenic species by CuFe2O4 activated peroxymonosulfate process

para-arsanilic acid (p-ASA), as a major phenylarsonic feed additive, was used annually in many countries. Once it enters the water environment, p-ASA would be transformed into hypertoxic inorganic arsenic species, causing severe arsenic pollution. In this study, magnetic copper ferrite (CuFe2O4) was applied to activate peroxymonosulfate (PMS) for p-ASA removal and synchronous control of the released inorganic arsenic species. Results showed that CuFe2O4/PMS system presented favorable oxidation ability and close to 85% of 10 mg/L p-ASA was eliminated under the condition of simultaneous dosing 0.2 g/L CuFe2O4 and 1 mM PMS. The rapid decomposition of p-ASA resulted from homogeneous PMS oxidation and the attack of reactive oxygen species (i.e., SO4−, HO and O2−), which was involved the heterogeneous PMS activation through the cycles between Fe(II)/Fe(III) and Cu(II)/Cu(I). Meanwhile, the released inorganic arsenic species during p-ASA degradation were found to be controllable via the adsorption on CuFe2O4 surface and metal hydroxyl groups played the crucial role. CuFe2O4/PMS system exhibited the stable and efficient performance within the broad range of pH 3.0–11.0. The existence of common anions (Cl−, NO3−, HCO3−, SO42−) and humic acid presented the slight inhibition for p-ASA degradation. The reduction of initial p-ASA concentration favored the p-ASA removal. Besides, the catalyst retained a favorable reactivity and stability even after four successive cycles and almost no metal leaching was observed. The rational degradation pathway was mainly involved in the cleavage of AsC bond, oxidation of amino group, substitution and oxidation of hydroxyl group. The transformation of arsenic species could be divided into the release of inorganic arsenic species, the oxidation of As(III) into As(V) and the adsorption of As(V) by CuFe2O4.

Highly effective oxidation of roxarsone by ferrate and simultaneous arsenic removal with in situ formed ferric nanoparticles

Roxarsone (ROX) is used in breeding industry to prevent infection by parasites, stimulate livestock growth and improve pigmentation of livestock meat. After being released into environment, ROX could be bio-degraded with the formation of carcinogenic inorganic arsenic (As) species. Here, ferrate oxidation of ROX was reported, in which we studied total-As removal, determined reaction kinetics, identified oxidation products, and proposed a reaction mechanism. It was found that the apparent second-order rate constant (kapp) of ferrate with ROX was 305 M−1s−1 at pH 7.0, 25 °C, and over 95% of total As was removed within 10 min when ferrate/ROX molar ratio was 20:1. Species-specific rate constants analysis showed that HFeO4− was the dominant species reacting with ROX. Ferrate initially attacked AsC bond of ROX and resulted in the formation of arsenate and 2-nitrohydroquinone. The arsenate was simultaneously removed by ferric nanoparticles formed in the reduction of ferrate, while 2-nitrohydroquinone was further oxidized into nitro-1,4-benzoquinone. These results suggest that ferrate treatment can be an effective method for the control of ROX in water treatment.

Photooxidation of p-Arsanilic Acid in Aqueous Solution by UV/Persulfate Process

Used as a kind of feed additive, p-arsanilic acid can pose a potential risk to organisms when abandoned in the environment. The photodegradation of p-ASA was investigated under UV-C irradiation in the presence of persulfate (PS) in this work. The addition of PS facilitated the decomposition of p-ASA and notably, the presence of 50 mmol PS brought about a nearly complete mineralization after 3 h, while an insignificant total organic carbon (TOC) removal was observed under UV irradiation (λ = 254 nm) only. Experimental results proved that sulfate radical (SO4•−) was responsible for the promotion effect. The cleavage of As-C bond released inorganic arsenic and caused the occurrence of various organic products, for example, hydroxybenzaldehyde, nitrobenzene, benzenediol sulfate, and biphenylarsinic acid. The application of PS with UV-C light may throw a light on thorough treatment for p-ASA containing wastewater.

Atomic Mechanism of Arsenic Monolayer Doping on oxide-free Silicon(111)

AbstractThe reaction pathway for shallow arsenic doping of silicon by methylarsenic acid molecules directly grafted on oxide-free, H-terminated Si(111) surfaces is unraveled combining Infrared absorption spectroscopy, X-ray Photoelectron Spectroscopy, Low Energy Ion Scattering and ab initio Molecular Dynamics simulations. The overall driving force is identified as a thermodynamic instability of As+5 in contact with silicon, which initiates a self-decomposition of chemisorbed methylarsenic molecules at ∼600 K. As the temperature is increased, the As-C bond breaks -- the weakest link of the adsorbed molecule -- with release of the organic ligand and a rearrangement from a monodentate to a bidentate bonding configuration. In this process, oxygen atoms evolve by partial desorption as H2O and partial incorporation into the surface Si atom backbonds. At ∼1050 K, diffusion of As into the sub-surface region of silicon is observed. There is no evidence for As desorption and no remaining C contamination.

Stepwise Formation of a 1,3-Butadiene Analogue of Mixed Heavier Group 15 Elements.

The reaction of the phosphinidene complex [Cp*P{W(CO)5}2] (1 a) with di-tert-butylcarboimidophosphene leads to the P-C cage compound 6 and the Lewis acid-base adduct [Cp*P{W(CO)5}2(CNtBu)] (2 a). In contrast, the arsinidene complex shows a different reactivity. At low temperatures, the arsaphosphene complex [{W(CO)5}{η(2)-(Cp*)As=P(tBu)}{W(CO)5}] (3) is formed. At these temperatures, 3 reacts further with a second equivalent of carboimidophosphene to form [{W(CO)5}{η(2)-{(Cp*)(tBu)P}As=P(tBu)}{W(CO)5}] (5), probably by the insertion of a phosphinidene unit (tBuP) into an As-C bond. In contrast, at room temperature 3 reacts further by a radical-type reaction to form [{(tBu)P=As-As=P(tBu)}{W(CO)5}4] (4). Compound 4 is the first example of a neutral, 1,3-butadiene analogue containing only mixed heavier Group 15 elements. It consists of two P=As double bonds connected by arsenic atoms.

Adsorption and photocatalytic decomposition of roxarsone by TiO2 and its mechanism

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid) has been widely used as organic arsenic additive in animal industry. In this study, the adsorption of roxarsone on TiO₂ under dark conditions, the photocatalytic decomposition of roxarsone under UV/TiO₂, and the possible photocatalytic pathway were investigated. At the initial concentration of 5-35 mg/L, the adsorption of roxarsone fitted well with the pseudo-second-order kinetics. The isotherms analysis showed that the Langmuir model was better than the Freundlich and Dubinin–Radushkevich models for describing the adsorption process. After 7 h of photocatalytic decomposition, a complete disappearance of roxarsone was achieved. The pH value has a significant effect on both adsorption and photocatalytic decomposition of roxarsone. The results of high-performance liquid chromatography-hydride generation-atomic fluorescence spectrometry (HPLC-HG-AFS) and gas chromatography-mass spectrometry (GC/MS) analyses proved the cleavage of the As-C bond during the photocatalytic decomposition process by TiO2 and the intermediates of the decomposition. Based on the results, a possible photocatalytic decomposition pathway was proposed.

A first-principles investigation of oxygen reduction reaction catalysis capabilities of As decorated defect graphene.

Single and multiple As adatom adsorptions on double vacancy (DV) defect graphene sheets are extensively analyzed using dispersive force corrected density functional theory (DFT). Defect pentagonal and heptagonal bridge sites and the immediate neighborhood of the defect center are found to be most favorable for this purpose. Quantitative analysis of electronic structures revealed the As-C bonding to be mostly ionic in nature with some covalency arising from the overlap of As p states and C p states. For multiple As adatoms adsorption in close vicinity, ionicity of the As-C bonds are found to decrease to support As-As cohesion; the net result of which is manifested as better binding of dioxygen molecule with them and additional weakening of the O-O bond in the adsorbed state. Free energy profile of oxygen reduction reaction (ORR) cycle using multiple As atom adsorbed DV graphene as electrocatalyst predicts high affinity towards four electron process and forbids the formation of H2O2via two electron process. Other traits, such as no intermediate O-O-H formation and high stability of the catalytic system throughout the reaction process indicate As adatoms adsorbed on DV graphene system to be efficient and highly stable as an alternate Pt free ORR electrocatalyst.

Arsenic Speciation in Blue Mussels (Mytilus edulis) Along a Highly Contaminated Arsenic Gradient

Arsenic is naturally present in marine ecosystems, and these can become contaminated from mining activities, which may be of toxicological concern to organisms that bioaccumulate the metalloid into their tissues. The toxic properties of arsenic are dependent on the chemical form in which it is found (e.g., toxic inorganic arsenicals vs nontoxic arsenobetaine), and two analytical techniques, high performance liquid chromatography coupled with inductively coupled plasma mass spectrometry (HPLC-ICP-MS) and X-ray absorption spectroscopy (XAS), were used in the present study to examine the arsenic species distribution in blue mussels (Mytilus edulis) obtained from an area where there is a strong arsenic concentration gradient as a consequence of mining impacted sediments. A strong positive correlation was observed between the concentration of inorganic arsenic species (arsenic compounds with no As-C bonds) and total arsenic concentrations present in M. edulis tissues (R(2) = 0.983), which could result in significant toxicological consequences to the mussels and higher trophic consumers. However, concentrations of organoarsenicals, dominated by arsenobetaine, remained relatively constant regardless of the increasing As concentration in M. edulis tissue (R(2) = 0.307). XANES bulk analysis and XAS two-dimensional mapping of wet M. edulis tissue revealed the presence of predominantly arsenic-sulfur compounds. The XAS mapping revealed that the As(III)-S and/or As(III) compounds were concentrated in the digestive gland. However, arsenobetaine was found in small and similar concentrations in the digestive gland as well as the surrounding tissue suggesting arsenobetaine may being used in all of the mussel's cells in a physiological function such as an intracellular osmolyte.

The Fourier transform microwave spectrum of the arsenic dicarbide radical (CCAs: X̃Π1∕22) and its C13 isotopologues

The pure rotational spectrum of the CCAs radical in its ground electronic and spin state, X (2)Pi(12), has been measured using Fourier transform microwave techniques in the frequency range of 12-40 GHz. This species was created in a supersonic expansion from a reaction mixture of AsCl(3) and C(2)H(2) or CH(4) diluted in high pressure argon, using a pulsed nozzle containing a dc discharge source. Three rotational transitions were measured for the main isotopologue, (12)C(12)CAs, in the Omega=12 ladder; both lambda-doubling and arsenic (I=32) hyperfine interactions were observed in these spectra. In addition, two to four rotational transitions were recorded for the (13)C(13)CAs, (13)C(12)CAs, and (12)C(13)CAs species. In these three isotopologues, hyperfine splittings were also resolved arising from the (13)C nuclei (I=12), creating complex spectral patterns. The CCAs spectra were analyzed with a case (a) Hamiltonian, and effective rotational, lambda-doubling, and arsenic and carbon-13 hyperfine constants were determined for the Omega=12 ladder. From the effective rotational constants of the four isotopologues, an r(m) ((1)) structure has been derived with r(C-C)=1.287 A and r(C-As)=1.745 A. These bond lengths indicate that the predominant structure for arsenic dicarbide is C=C=As, with some contributing C[Triple Bond]C and C[Triple Bond]As triple bond characters. The hyperfine constants established in this work indicate that about 23 of the unpaired electron density lies on the arsenic atom, with the remaining percentage on the terminal carbon. The value of the arsenic quadrupole coupling constant (eqQ=-202 MHz) suggests that the As-C bond has a mixture of covalent and ionic characters, consistent with theoretical predictions that both pi backbonding and electron transfer play a role in creating a linear, as opposed to a cyclic, structure for certain heteroatom dicarbides.

Hydride generation activity of arsenosugars and thioarsenicals

The major arsenosugar compounds have been reported to be hydride-generation-active, however to a lesser extent in comparison with the inorganic arsenicals. We report here for the first time the identity and quantity of the volatile arsenicals generated by As-sugar-SO(3), As-sugar-SO(4), dimethylarsinoyl acetic acid and dimethylarsinoyl ethanol. Only one major volatile compound was identified for all four compounds studied: dimethylarsine. This means that the As-C bond to the longer carbon chain was cleaved during the hydride-generation process. Theoretical calculations at the RHF/6-31G(d,p) ab initio level confirm that this As-C bond is much weaker than the As-CH(3) bonds. Furthermore, it was revealed that the sulphur analogue of dimethylarsinic acid (DMAS ) is hydride-generation-active at pH 7 in contrast to dimethylarsinic acid, despite the fact that arsenic is also pentavalent. This has been substantiated by the calculation of the change in susceptibility of the arsenic towards nucleophilic attack when oxygen is replaced by sulphur. Hence, DMAS can easily be mistaken for a trivalent arsenic species.

Bulky triarylarsines are effective ligands for palladium catalysed Heck olefination

The four arsines, As{C6H3(o-CH3)(p-Z)}3{Z=H (2a) or OMe (2b)} and As{C6H3(o-CHMe2)(p-Z)}3{Z=H (2c) or OMe (2d)} react with [PdCl2(NCPh)2] or [PtCl2(NCBu(t))2] to give trans-[MCl2L2] or trans-[M2Cl2(mu-Cl)2L2]. The crystal structures of trans-[PdCl2(2a)2] and [PtCl2(2d)2] have been determined, the latter as its dichloromethane solvate. The structures show that in these complexes, the ligands adopt gga type conformations as do all analogous tri-o-tolyl- and tri-o-isopropylphenylphosphines in square-planar and octahedral complexes. The variable-temperature NMR behaviour of the complexes shows that they are fluxional due to restricted As-C bond rotation. The rate of the fluxionality is more rapid than in the analogous phosphine complexes and this is associated with longer As-C and As-M bonds allowing more free movement. The catalytic activity of the palladium complexes of the arsines and their phosphine analogues for the reaction of 4-bromoacetophenone and n-butyl acrylate has been screened. The results show that the arsines are generally superior to the phosphines as ligands for this catalysis. Tri(o-isopropylphenyl)phosphine and tri(o-isopropylphenyl)arsine are superior to tri-o-tolylphosphine as ligands for this Heck reaction and a p-methoxy substituent improves the arsine catalyst but not the phosphine catalyst. The phosphine catalysts are superior to the arsine catalysts for the reaction of 4-chloroacetophenone and n-butyl acrylate. These observations are discussed in the context of ligand stereoelectronic effects, as measured by the Tolman electronic parameter, nuCO of the [NiL(CO)3]{L=AsAr3 or PAr3}.

Degradation of phenylarsonic acid and its derivatives into arsenate by hydrothermal treatment and photocatalytic reaction

The degradation of phenylarsonic acid (PA) and its derivatives by hydrothermal treatment (HTT) was examined, especially focusing on the effect of adding H 2 O 2 upon the degradation efficiency. The degradation was assessed by the generation of arsenate resulting from the cleavage of As-C bonds in the PA derivatives. When PA (without substituents) was subjected to an HTT with H 2 O 2 (H 2 O 2 -HTT; 0.5-1% H 2 O 2 ) at 175-200 °C, PA was almost completely degraded into arsenate, whereas an HTT with NaOH (NaOH-HTT; 3 M NaOH) at the temperatures provided almost no degradation. The H 2 O 2 -HTT also worked well for the degradation of PA derivatives with hydroxy and/or nitro groups on the phenyl ring. However, the degradation of aminophenylarsonic acids was not favorably performed by the H 2 O 2 -HTT. The effect of the structure of PA derivatives upon the degradation susceptibility was discussed. A photocatalytic reaction using TiO 2 was also attempted for the degradation of PA derivatives.

From the New Arsaalkene ArAsC(Br)SiMe3 to the First Stable Arsaallene, ArAsCCR2 (Ar = 2,4,6-Tri-tert-butylphenyl, CR2 = Fluorenylidene)

The first stable arsaallene, ArAsCCR2 1 (Ar = 2,4,6-tri-tert-butylphenyl, CR2 = fluorenylidene), has been synthesized by a one-pot procedure involving the successive addition of n-butyllithium and fluorenone to the new arsaalkene ArAsC(Br)SiMe3, which presents a Z configuration and a short AsC bond length (1.789(3) Å). An X-ray crystallographic structure determination of air and thermally stable 1 proves its allenic geometry (AsC(1)C(2) bond angle 169.72(19)°, angle between the fluorenylidene plane and the C(15)AsC(1)C(2) mean plane 79.3°) with very short AsC(1) and C(1)C(2) double-bond lengths (1.754(2) and 1.314(3) Å).

Acyclic, ring, and cage As,C compounds from trimethylsilyl ylides and AsCl3

From the reaction of trimethylsilyl ylides with AsCl3 the dichloroarsanyl ylides 2b and 5b are obtained. As shown by X-ray structure determination, their AsCl2 groups deviate systematically from the symmetric orientation. This conformation enables an effective charge transfer from the ylide moiety to one of the As-Cl bonds, which as a consequence is up to 15 pm longer than the other. At the same time the length of the As-C bonds in 2b and 5b indicates a partial double bond. The effects observed here are of the same type as those observed for the corresponding dichlorophosphanyl ylides; they are, however, more pronounced. The 1:1 condensation of the bis(trimethylsilyl) ylide 3 and AsCl3 yields the oligomers (Ph3PCAsCl)2,3,4. The dimer 7b has a diarsetane structure. HCl adds readily to one of its As-C bonds without opening it. The trimer and the tetramer are ionic. The cation of the trimer forms a six-membered ring with a delocalized arsenium/phosphonium charge, the cation of the tetramer forms a barrelane cage with a phosphonio substituent, and the anion is AsCl4- in both cases (10, 13). An arsa-phosphocyanine cation as in 10 is also part of the diphosphonio isoarsindolide tetrachloroarsenate(III) 12. The structures of 7b.HCl, 10, and 13 reflect again an ylide to As-Cl charge transfer. The As-Cl bonds of 13 are by far the longest ones known for a chloroarsine (average 249 pm).