Röntgenographische und schwingungsspektroskopische Untersuchung der Sulvanitmischkristalle Cu3Nb(SxSe1−x)4, Cu3Nb(SexTe1−x)4, und Cu3Ta(SxSe1−x)4 und Cu3Ta(SexTe1−x)4

X-Ray and Vibrational Studies of Sulvanite Mixed Cystals Cu₃Nb(S_xSe_1?x)₄, Cu₃Nb(Se_xTe_1?x)₄, Cu₃Ta(S_xSe_1?x)₄ and Cu₃Ta(Se_xTe_1?x)₄ Solid solutions Cu₃Nb(S_xSe_1?x)₄, Cu₃Nb(Se_xTe_1?x)₄, Cu₃Ta(S_xSe_1?x)₄ and Cu₃Ta(Se_xTe_1?x)₄ with sulvanite structure have been prepared in the range 0 ≤ x ≤ 1. The lattice constants in all systems obey the Vegard rule. Infrared and Raman spectra have been measured. The spectra of the compounds with mixed anion sublattices show additional peaks, compared to those of the end members, because besides the polyhedra MX₄ and MY₄ also groups MX₃Y, MX₂Y₂, and MXY₃ are present, and all groups are able to oscillate independently. By comparison of the peak intensities and the statistical frequency of the groups according to the composition, the additional valence vibrations could be attributed to the groups.     

XPS study on valence band structures of transition-metal trisulfides,TiS3, NbS3, and TaS3

Transition-metal trisulfides, TiS₃, NbS₃, and TaS₃, with a quasi-one-dimensional structure are investigated by X-ray photoelectron spectroscopic (XPS) measurements to obtain information on the valence band structures. The band structures at the Fermi level of these compounds correspond well to their transport properties. A shoulder is observed at the top of the valence band in NbS₃ and TaS₃, suggesting that this band is made up of the metal d_z² electrons. The d_z² band is occupied in NbS₃ and TaS₂ and empty in TiS₃. The characteristic features at the top of the valence band in NbS₃ imply the occurrence of d_z² band separation, which leads to a semiconducting nature.     

Disordered La3Cu4.88Se7

The crystal structure of copper(I) lanthanum selenide, La₃Cu_4.88Se₇, obtained from the La₂Se₃–Cu₂Se quasi‐binary system, has been investigated using X‐ray single‐crystal diffraction. The positions of the La and Se atoms are ordered and lie on mirror planes, whereas all positions for the Cu atoms are partially occupied. The crystal is built from edge‐sharing [LaSe₆] and [LaSe₇] polyhedra. The five positions for the Cu atoms determine an ionic diffusion pathway in the structure.     

Intermolecular Se···I Interactions Identified in Cu11(μ9‐Se)(μ3‐I)3[Se2P(OEt)2]6 Form a One Dimensional Polymeric Chain

The undecanuclear copper cluster Cu₁₁(μ9‐Se)(μ₃‐I)₃[Se₂P(OEt)₂]₆ 1 , has been isolated along with Cu₈(μ₈‐Se)[Se₂P(OEt)₂]₆ 2 , from the reaction of NH₄Se₂P(OEt)₂, Cu(CH₃CN)₄PF₆, and Bu₄NI in a molar ratio of 3:2:2 in diethyl ether. The molecular formulation of 1 was confirmed by elemental analysis, positive FAB mass spectrometry, multinuclear NMR (¹H, ³¹P, and ⁷⁷Se), and X‐ray diffraction. In cluster 1 eleven copper atoms adopt the geometry of a 3,3,4,4,4‐pentacapped trigonal prism with a selenium atom in the center. The coordination geometry for the central, nonacoordinated selenium atom is tricapped trigonal prismatic. In addition, the central core Cu₁₁Se is further stabilized by three iodides and six dsep ligands. Besides, weak inter‐molecular Se···I interactions (3.949–3.972 Å) are uncovered and form a one dimensional polymeric chain.     

A crystallographic description of experimentally identified formation reactions of Cu(In,Ga)Se2

This work describes solid-state reactions for the formation of the chalcopyrite compounds CuInSe₂, CuGaSe₂ and Cu(In,Ga)Se₂ on atomic scale. The most important chalcopyrite formation reactions which were identified by the authors by real-time in situ X-ray diffraction in preceding experiments are (A) CuSe+InSe→CuInSe₂, (B) Cu₂Se+2 InSe+Se→2 CuInSe₂ and (C) Cu₂Se+In₂Se₃→2 CuInSe₂. During the selenistaion of a metallic precursor containing gallium a separate fourth reaction occurs: (D) Cu₂Se+Ga₂Se₃→2 CuGaSe₂. The quaternary compound is finally formed by interdiffusion of CuInSe₂ with CuGaSe₂ (E). These five reactions differ in their activation energy and reaction speed. We explain these differences qualitatively by analysing the involved crystal structures for each reaction. It turns out that all reactions involved in the formation of Cu(In,Ga)Se₂ are promoted by epitaxial relations, which facilitates the formation of polycrystalline thin films at temperatures much below those necessary for single crystal growth. Recommendations for the growth of larger grains of Cu(In,Ga)Se₂ containing fewer defects are given.     

High-pressure syntheses of TaS3, NbS3, TaSe3, and NbSe3 with NbSe3-type crystal structure

Transition metal trichalcogenides TaSe₃, TaS₃, NbSe₃ and NbS₃ were prepared under the reaction conditions of 2 GPa, 700°C, 30 min. NbSe₃ is exactly the same as that obtained in the usual sealed-tube method. The other products are modifications of each usual phase. They have crystal structures very similar to that of NbSe₃. The lattice parameters are a = 10.02Å, b = 3.48 Å, c = 15.56 Å, β = 109.6° for TaSe₃, a = 9.52 Å, b = 3.35 Å, c = 14.92 Å, β = 110.0° for TaS₃, and a = 9.68 Å, b = 3.37 Å, c = 14.83 Å, β = 109.9° for NbS₃. In spite of the similarity in their crystal structures, these high-pressure phases show a variety of electrical transport properties. TaSe₃ is a superconductor having T_c at 1.9 K. TaS₃ is a semiconductor with two transitions at 200 and 250 K. NbS₃ is a semiconductor with E_a = 180 MeV.     

Mixed Cu2Se Hexagonal Nanosheets@Co3Se4 Nanospheres for High-Performance Asymmetric Supercapacitors

Rational designing and constructing multiphase hybrid electrode materials is an effective method to compensate for the performance defects of the single component. Based on this strategy, Cu₂Se hexagonal nanosheets@Co₃Se₄ nanospheres mixed structures have been fabricated by a facile two-step hydrothermal method. Under the synergistic effect of the high ionic conductivity of Cu₂Se and the remarkable cycling stability of Co₃Se₄, Cu₂Se@Co₃Se₄ can exhibit outstanding electrochemical performance as a novel electrode material. The as-prepared Cu₂Se@Co₃Se₄ electrode displays high specific capacitance of 1005 F g⁻¹ at 1 A g⁻¹ with enhanced rate capability (56 % capacitance retention at 10 A g⁻¹), and ultralong lifespan (94.2 % after 10 000 cycles at 20 A g⁻¹). An asymmetric supercapacitor is assembled applying the Cu₂Se@Co₃Se₄ as anode and graphene as cathode, which delivers a wide work potential window of 1.6 V, high energy density (30.9 Wh kg⁻¹ at 0.74 kW kg⁻¹), high power density (21.0 Wh kg⁻¹ at 7.50 kW kg⁻¹), and excellent cycling stability (85.8 % after 10 000 cycles at 10 A g⁻¹).     

Monoclinic Cu2Se3Sn

A previously unknown modification of dicopper(I) triselenostannate(IV), Cu₂Se₃Sn, has been obtained from the Cu₂Se–SnSe₂ quasi‐binary system and investigated using X‐ray single‐crystal diffraction. The Se atoms are stacked in a closest‐packed arrangement with the layers in the sequence ABC. The Cu atoms occupy one‐third of the tetrahedral interstices, whereas the Sn atoms are located in one‐sixth of the tetrahedral interstices. All the atoms occupy general positions. The structure possesses pseudo‐inversion symmetry. The Cu₂Se₃Sn structure investigated in this paper (96 atoms per unit cell, ordered distribution of Cu and Sn over 12 cation positions) is a superstructure of the reported cubic (eight atoms per unit cell, random distribution of Cu and Sn over one cation position) and monoclinic (24 atoms per unit cell, ordered distribution of Cu and Sn over three cation positions) modifications.     

Bis­[bis(N,N‐diethyl‐1,1‐di­seleno­car­bam­ato)copper(II)], [Cu(Se2CNEt2)2]2

The title centrosymmetric Cu^II binuclear complex, bis(μ‐N,N‐diethyl‐1,1‐di­seleno­carbamato‐Se,Se′:Se)­bis­[(N,N‐diethyl‐1,1‐di­seleno­carbamato‐Se,Se′)copper(II)], [Cu(Se₂CNEt₂)₂]₂ or [Cu₂(C₅H₁₀NSe₂)₄], is built from two symmetry‐related [Cu{Se₂CN(Et)₂}₂] units by pairs of Cu—Se bonds. The coordination geometry at the unique Cu atom is distorted square pyramidal, with Cu—Se distances in the range 2.4091 (11)—2.9095 (10) Å.     

Die Seltenerdmetallpolyselenide Gd8Se15, Tb8Se15−x,Dy8Se15−x,Ho8Se15−x,Er8Se15−x und Y8Se15−x (0 < x ≤ 0.3) – Zunehmende Fehlordnung in ausgedünnten,planaren Selenschichten

The Rare Earth Metal Polyselenides Gd₈Se₁₅, Tb₈Se_15?x, Dy₈Se_15?x, Ho₈Se_15?x, Er₈Se_15?x, and Y₈Se_15?x – Increasing Disorder in Defective Planar Selenium Layers Single crystals of the rare earth metal polyselenides Gd₈Se₁₅, Tb₈Se_15?x, Dy₈Se_15?x, Ho₈Se_15?x, Er₈Se_15?x, and Y₈Se_15?x (0 < x ≤ 0.3) have been prepared by chemical transport reactions (1120 K→ 970 K, 14 days, I₂ as carrier) starting from pre‐annealed powders of nominal compositions between LnSe₂ and LnSe_1.9. The isostructural title compounds adopt a 3 × 4 × 2 superstructure of the ZrSSi type and can be described in space group Amm2 with lattice parameters of a = 12.161(1) Å, b = 16.212(2) Å and c = 16.631(2) Å (Gd₈Se₁₅), a = 12.094(2) Å, b = 16.123(2) Å and c = 16.550(2) Å (Tb₈Se_15?x), a = 12.036(2) Å, b = 16.060(2) Å and c = 16.475(2) Å (Dy₈Se_15?x), a = 11.993(2) Å, b = 15.999(2) Å and c = 16.471(2) Å (Ho₈Se_15?x), a = 11.908(2) Å, b = 15.921(2) Å and c = 16.428(2) Å (Er₈Se_15?x), and a = 12.045(2) Å, b = 16.072(3) Å and c = 16.626(3) Å (Y₈Se_15?x), respectively. The structure consists of puckered [LnSe] double slabs and planar Se layers alternating along [001]. The planar Se layers contain a disordered arrangement of dimers, Se^2? and vacancies. All compounds are semiconducting and contain trivalent rare earth metals (Ln³⁺).     

A Directed Route to Colloidal Nanoparticle Synthesis of the Copper Selenophosphate Cu3PSe4

The first colloidal nanoparticle synthesis of the copper selenophosphate Cu₃PSe₄, a promising new material for photovoltaics, is reported. Because the formation of binary copper selenide impurities seemed to form more readily, two approaches were developed to install phosphorus bonds directly: 1) the synthesis of molecular P₄Se₃ and subsequent reaction with a copper precursor, (P‐Se)+Cu, and 2) the synthesis of copper phosphide, Cu₃P, nanoparticles and subsequent reaction with a selenium precursor, (Cu‐P)+Se. The isolation and purification of Cu₃P nanoparticles and subsequent selenization yielded phase‐pure Cu₃PSe₄. Solvent effects and Se precursor reactivities were elucidated and were key to understanding the final reaction conditions.     

Compounds in the system Cu2SeAs2Se3

The phase diagram Cu₂SeAs₂Se₃ was investigated by thermal and X-ray methods. Cu₂Se has a limited solubility for As₂Se₃ (5 mole% at 769 K). The stoichiometric compound Cu₃AsSe₃ exists between 696 and 769 K. Cu₄As₂Se₅, a phase at 66.6 mole% Cu₂Se, decomposes peritectically at 746 K. The narrow homogeneity range (4 mole% at 683 K) extends far into the ternary space. CuAsSe₂ also decomposes peritectically at 683 K. A degenerated eutectic between CuAsSe₂ and As₂Se₃ was found at 641 K. Single crystals of Cu₄As₂Se₅ were grown in a salt melt. A metastable modification of the high-temperature phase Cu₃AsSe₃ can be obtained by quenching. Cu₄As₂Se₅ (space group R3, lattice constants a = 1404.0(1) pm, c = 960.2(1) pm), Cu₆As₄Se₉, obtained by Cambi and Elli, and Cu₇As₆Se₁₃ of Takeuchi and Horiuchi are different versions of a sphalerite-type compound with a broad homogeneity range in the system CuAsSe. CuAsSe₂ is possibly monoclinic with lattice parameters of a = 946.5(1) pm, b = 1229.3(1) pm, c = 511.7(1) pm, and β = 98.546(4)°. The enthalpy of mixing of Cu₂Se and As₂Se₃ in the liquid state is endothermic.     

Synthese und Strukturen neuer selenido‐ und selenolatoverbrückter Kupfercluster: [Cu38Se13(SePh)12(dppb)6] (1), [Cu(dppp)2][Cu25Se4(SePh)18(dppp)2] (2), [Cu36Se5(SePh)26(dppa)4] (3), [Cu58Se16(SePh)24(dppa)6] (4) und [Cu3(SeMes)3(dppm)] (5)

Syntheses and Crystal Structures of new Selenido‐ and Selenolato‐bridged Copper Clusters: [Cu₃₈Se₁₃(SePh)₁₂(dppb)₆] (1), [Cu(dppp)₂][Cu₂₅Se₄(SePh)₁₈(dppp)₂] (2), [Cu₃₆Se₅(SePh)₂₆(dppa)₄] (3), [Cu₅₈Se₁₆(SePh)₂₄(dppa)₆] (4), and [Cu₃(SeMes)₃(dppm)] (5) The reactions of copper(I) chloride or copper(I) acetate with monodentate phosphine ligands (PR₃; R = organic group) and Se(SiMe₃)₂ have already lead to the formation of CuSe clusters with up to 146 copper and 73 selenium atoms. If the starting materials and the bidentate phosphine ligands (Ph₂P–(CH₂)_n–PPh₂, n = 1: dppm, n = 3: dppp, n = 4: dppb; Ph₂P–C≡C–PPh₂: dppa) and silylated chalcogen derivates are changed (RSeSiMe₃; R = Ph, Mes) a series of new CuSe clusters can be synthesized. From single crystal X‐ray structure analysis one can characterise [Cu₃₈Se₁₃(SePh)₁₂(dppb)₆] ( 1 ), [Cu(dppp)₂] · [Cu₂₅Se₄(SePh)₁₈(dppp)₂] ( 2 ), [Cu₃₆Se₅(SePh)₂₆(dppa)₄] ( 3 ), [Cu₅₈Se₁₆(SePh)₂₄(dppa)₆] ( 4 ) and [Cu₃(SeMes)₃(dppm)] ( 5 ). In this new class of CuSe clusters, compounds 1 and 4 possess a spherical cluster skeleton, wheras 2 and 3 have a layered cluster core.     

Interaction between Cr2Se3 and Cu2GeSe3

The interaction along the Cu₂GeSe₃-Cr₂Se₃ join has been investigated using differential thermal and X-ray powder diffraction analyses. It has been found that the join is quasi-binary with a degenerate eutectic based on the Cu₂GeSe₃ compound. Two new quaternary compounds have been found along the join, namely, Cu₂GeCr₆Se₁₂ and the γ phase. The phase is formed at 915°C by the peritectic reaction L + β-Cr₂Se₃ = γ and has the primary crystallization region up to 9 mol % Cr₂Se₃ in the temperature range 758–915°C. The room-temperature homogeneity range of the γ phase is 65–70 mol % Cr₂Se₃. The Cu₂GeCr₆Se₁₂ compound is formed by the peritectoid reaction γ + β-Cr₂Se₃=Cu₂GeCr₆Se₁₂ at 880°C, and its homogeneity range is 73–79 mol %. The X-ray reflections of the γ phase are indexed for the tetragonal crystal system with the unit cell parameters a = 12.043 Å and c = 9.180 Å. Samples with ferromagnetic properties are found in the homogeneity regions of both compounds.     

Chalkogenoniobate als Ausgangsverbindungen zur Darstellung neuer heterobimetallischer Niobium‐Münzmetall‐Chalkogenido‐Cluster

Chalcogenoniobates as Reagents for the Synthesis of New Heterobimetallic Niobium Coinage Metal Chalcogenide Clusters In the presence of phosphine chalcogenoniobates such as Li₃[NbS₄] · 4 CH₃CN ( I ), (NEt₄)₄[Nb₆S₁₇] · 3 CH₃CN ( II ) and (NEt₄)₂[NbE′₃(E^tBu)] ( III a : E′ = E = S; III b : E = Se, E′ = S; III c : E = E′ = Se) respectively react with copper and gold salts to give a number of new heterobimetallic niobium copper(gold) chalcogenide clusters. These clusters show metal chalcogenide units already known from the complex chemistry of the tetrachalcogenometalates [ME₄]^n– (M = V, n = 3, E = S; M = Mo, W, n = 2, E = S, Se). The compounds 1 – 8 owe a central tetrahedral [NbE₄] structural unit, which coordinates η² from two to five coinage metal atoms, employing the chalcogenide atoms of the [NbE₄] edges. The compounds 9 – 11 have a [M′₂Nb₂E₄] (M′ = Cu, Au) heterocubane unit in common, involving a metal metal bond between the niobium atoms, while the compounds 12 and 13 show a complete and 14 an incomplete [M′₃NbE₃X] heterocubane structure (X = Cl, Br). 15 consists of a Cu₆Nb₂ cube with the six planes capped by μ₄ bridging selenide ligands forming an octahedra. The compounds 1 – 15 are listed below: (NEt₄) [Cu₂NbSe₂S₂(dppe)₂] · 2 DMF ( 1 ), [Cu₃NbS₄(PPh₃)₄] ( 2 ), [Au₃NbSe₄(PPh₃)₄] · Et₂O ( 3 ), [Cu₄NbS₄Cl(PCy₃)₄] ( 4 ), [Cu₄NbS₄Cl(P^tBu₃)₄] · 0,5 DMF ( 5 ), [Cu₄NbSe₄(NCS)(P^tBu₃)₄] · DMF ( 6 ), [Cu₄NbS₄(NCS)(dppm)₄] · Et₂O ( 7 ), [Cu₅NbSe₄Cl₂‐ (dppm)₄] · 3 DMF ( 8 ), [Cu₂Nb₂S₄Cl₂(PMe₃)₆] · DMF ( 9 ), [Au₂Nb₂Se₄Cl₂(PMe₃)₆] · DMF ( 10 ), (NEt₄)₂[Cu₃Nb₂S₄(NCS)₅(dppm)₂(dmf)] · 4 DMF ( 11 ), [Cu₃NbS₃Br(PPh₃)₃(dmf)₃]Br · [CuBr(PPh₃)₃] · PPh₃ · OPPh₃ · 3 DMF ( 12 ), [Cu₃NbS₃Cl₂(PPh₃)₃(dmf)₂] · 1.5 DMF ( 13 ), (NEt₄)[Cu₃NbSe₃Cl₃(dmf)₃] ( 14 ), [Cu₆Nb₂Se₆O₂(PMe₃)₆] ( 15 ). The structures of these compounds were obtained by X‐ray single crystal structure analysis.     

Studies of the system TaS2−xSex

Single crystal and powder samples of the system TaS_2?xSe_x have been prepared and studied. The range of solubility was found to extend from x = 0 to x = 2.0. X-Ray analysis has shown that mixed anion samples exhibit a series of hexagonal layered polymorphs similar to those found in TaS₂ and TaSe₂, with the a and c lattice parameters increasing monotonically from TaS₂ to TaSe₂. Electrical transport properties were measured on single crystals and found to be similar to the end compositions. Organic molecules such as pyridine and collidine were found to intercalate TaS_2?xSe_x for x ≦ 1.4, and superconducting transition temperatures were measured for both intercalated and unintercalated samples. The highest T_c obtained was 4.1 K in the 4H(c) phase of the sample TaS_1.6Se_0.4.     

Sb‐Triggered β‐to‐α Transition: Solvothermal Synthesis of Metastable α‐Cu2Se

Control over phase stabilities during synthesis processes is of great importance for both fundamental studies and practical applications. We describe herein a facile strategy for the synthesis of Cu₂Se with phase selectivity through a simple solvothermal method. In the presence and absence of SbCl₃, monoclinic α‐Cu₂Se and cubic β‐Cu₂Se can be synthesized, respectively. The formation of α‐Cu₂Se requires optimization of the Cu/Se molar ratio in the starting reagents, the reaction temperature, as well as the timing for the addition of SbCl₃. Differential scanning calorimetry of the synthesized α‐Cu₂Se has shown that a part of it undergoes a phase transition to β‐Cu₂Se at 135 °C, and that this phase transition is irreversible on cooling to ambient temperature. Kinetic studies have revealed that in the presence of Sb species the kinetically favored β‐Cu₂Se transforms to the thermodynamically favored α‐Cu₂Se. In this β‐to‐α phase transition process, the distribution of Cu ions in β‐Cu₂Se, as determined by the Cu/Se ratio and temperature, is likely to play a crucial role.     

Spinelle mit substituierten Nichtmetallteilgittern. IV. Rötgenographische Untersuchung der Systeme CuCr2(S1−xSex)4 und CuCr2(Se1−xTex)4

Spinels with substituted Nonmetal Sublattices. IV. CuCr₂(S_1?xSe_x)₄ and CuCr₂(Se_1?xTe_x)₄ Polycrystalline samples of the spinel system CuCr₂(S_1?xSe_x)₄ have been prepared with 0 ≤ x ≤ 1. We found that in the spinel system CuCr₂(Se_1?xTe_x)₄ no solid solution is existent in the range 0.01 ≤ x ≤ 0.70. When S is substituted by Se and Se by Te the lattice constants increase linearely by 0.52 Å and 0.81 Å respectively. The anion-sublattice shows random distribution of the chalcogen atoms, the chalcogen parameters u are constant in the system CuCr₂(S_1?xSe_x)₄ with a mean value of u = 0.382₉. The calculated anion-cation-distances lead to a covalent tetrahedral radius r_Cu = 1.23 Å. This radius is in agreement with the radius r_Cu = 1.22 Å of Cu spinels with Cu in the valence +1.     

Comparison characterization of copper selenide thin layers prepared on polyamide 6 films by sorption-diffusion method

Some earlier synthesized copper selenide (Cu _x Se) layers formed on the surface of polyamide 6 by sorption-diffusion method using potassium selenotrithionate (K₂SeS₂O₆) as precursor of selenium were characterized by the XRD, XPS and SEM methods. According to the results of the SEM studies, the most uniform Cu _x Se layers form at the 2.5 h polyamide seleniumized duration at the temperature of 60°C. The thickness of layers, which dependeds on the duration of seleniumization, changed in the range of 0.8–3.2 µm. The XRD patterns of not previously studied Cu _x Se layers showed their phase composition of six copper selenides: Cu₂Se, two phases of CuSe₂, Cu₃Se₂, berzellianite, Cu_2-x Se, and bellidoite Cu₂Se. Analysis of the XRD and XPS data shows that the macrostructure and composition of the Cu_xSe layers depend on the conditions of formation of these layers.      

Cyclische Polyselenidoarsenate(III) und -antimonate(III): PPh4[Se5AsSe], PPh4[AsSe6–xSx], (PPh4)2[As2Se6] · 2 CH3CN und (PPh4)2[Se6SbSe]2

Cyclic Polyselenidoarsenates(III) and Polyselenidoantimonates(III): PPh₄[Se₅AsSe], PPh₄[AsSe_6–xS _x ], (PPh₄)₂[As₂Se₆] · 2 CH₃CN, and (PPh₄)₂[Se₆SbSe]₂ In acetonitrile, AsCl₃ and sodiumphenolate formed Cl₂AsOPh which then was reacted with PPh₄Se₅ and finally with Na₂Se to yield PPh₄[Se₅AsSe]. With Na₂S instead of Na₂Se, PPh₄[AsSe_6–xS_x] was obtained; the sulfur contents increased with increasing reaction temperature and time (x = 0.21 to 1.09). With PPh₄Se₂ instead of PPh₄Se₅, (PPh₄)₂[1,4-As₂Se₆] · 2 CH₃CN and PPh₄[Se₅AsSe] were the products. With SbCl₃ instead of AsCl₃, (PPh₄)₂[Se₆SbSe]₂ formed. PPh₄[Se₅AsSe] can also be produced from As₂Se₃, PPh₄Br, Na₂Se and selenium in acetonitrile. The crystal structure of PPh₄[SeAsSe₅] is isotypic with PPh₄[S₅AsS] (X-ray structure analysis with 2414 observed reflexions, R = 0.038). The Se₅AsSe^– ion consists of a six-membered AsSe₅ ring in chair conformation, and the As atom has an additional terminal Se atom. The compounds PPh₄[AsSe_6–xS_x] have the same crystal structures, with sulfur atoms taking all selenium positions at random, but with a preference for the terminal position. The anion in (PPh₄)₂[As₂Se₆] · 2 CH₃CN also has a six-membered ring structure in chair conformation, with two arsenic atoms in positions 1 and 4. The centrosymmetric anion in (PPh₄)₂[Se₆SbSe]₂ consists of a central Sb₂Se₂ ring, and a Se₆ ligand is bonded in a chelating manner to each Sb atom (X-ray structure analysis with 2669 observed reflexions, R = 0.099). ⁷⁷Se-NMR spectra are reported.