Syntheses and Crystal Structures of Rb2B2Se7, Tl2B2Se7, Cs3B3Se10, and Tl3B3Se10: New Perseleno‐selenoborates with Polymeric Anionic Chains

The perseleno‐selenoborates Rb₂B₂Se₇ and Cs₃B₃Se₁₀ were prepared from the metal selenides, amorphous boron and selenium, the thallium perseleno‐selenoborates Tl₂B₂Se₇ and Tl₃B₃Se₁₀ directly from the elements in evacuated carbon coated silica tubes by solid state reactions at temperatures between 920 K and 950 K. All structures were refined from single crystal X‐ray diffraction data. The isotypic perseleno‐selenoborates Rb₂B₂Se₇ and Tl₂B₂Se₇ crystallize in the monoclinic space group I 2/a (No. 15) with lattice parameters a = 12.414(3) Å, b = 7.314(2) Å, c = 14.092(3) Å, β = 107.30(3)°, and Z = 4 for Rb₂B₂Se₇ and a = 11.878(2) Å, b = 7.091(2) Å, c = 13.998(3) Å, β = 108.37(3)° with Z = 4 for Tl₂B₂Se₇. The isotypic perseleno‐selenoborates Cs₃B₃Se₁₀ and Tl₃B₃Se₁₀ crystallize in the triclinic space group P1 (Cs₃B₃Se₁₀: a = 7.583(2) Å, b = 8.464(2) Å, c = 15.276(3) Å, α = 107.03(3)°, β = 89.29(3)°, γ = 101.19(3)°, Z = 2, (non‐conventional setting); Tl₃B₃Se₁₀: a = 7.099(2) Å, b = 8.072(2) Å, c = 14.545(3) Å, α = 105.24(3)°, β = 95.82(3)°, γ = 92.79(3)°, and Z = 2). All crystal structures contain polymeric anionic chains of composition ([B₂Se₇]^2–)_n or ([B₃Se₁₀]^3–)_n formed by spirocyclically fused non‐planar five‐membered B₂Se₃ rings and six‐membered B₂Se₄ rings in a molar ratio of 1 : 1 or 2 : 1, respectively. All boron atoms have tetrahedral coordination with corner‐sharing BSe₄ tetrahedra additionally connected via Se–Se bridges. The cations are situated between three polymeric anionic chains leading to a nine‐fold coordination of the rubidium and thallium cations by selenium in M₂B₂Se₇ (M = Rb, Tl). Coordination numbers of Cs⁺ (Tl⁺) in Cs₃B₃Se₁₀ (Tl₃B₃Se₁₀) are 12(11) and 11(9).     

Chloro- und Polyselenoselenate(II) Darstellung,Struktur und Eigenschaften von [Ph3(C2H4OH)P]2[SeCl4] · MeCN, [Ph4P]2[Se2Cl6] und [Ph4P]2[Se(Se5)2]

Chloro- and Polyselenoselenates(II): Synthesis, Structure, and Properties of [Ph₃(C₂H₄OH)P]₂[SeCl₄] · MeCN, [Ph₄P]₂[Se₂Cl₆], and [Ph₄P]₂[Se(Se₅)₂] By symproportionation of elemental selenium and SeCl₄ in polar protic solvents the novel chloroselenates(+II), [SeCl₄]^2? and [Se₂Cl₆]^2?, could be stabilized; they were crystallized with voluminous organic cations. They were characterized from complete X-ray structure analysis. Yellow-orange [Ph₃(C₂H₄OH)P]₂[SeCl₄] · MeCN (space group P1 , a = 10.535(4), b = 12.204(5), c = 16.845(6) Å, α = 77.09(3)°, β = 76.40(3)°, γ = 82.75(3)° at 140 K) contains in its crystal structure monomeric [SeCl₄]^2? anions with square-planar coordination of Se(+II). The mean Se? Cl bond length is 2.441 Å. In yellow [Ph₄P]₂[Se₂Cl₆] (space group P1 , a = 10.269(3), b = 10.836(4), c = 10.872(3) Å, α = 80.26(3)°, β = 79.84(2)°, γ = 72.21(3)° at 140 K) a dinuclear centrosymmetric [Se₂Cl₆]^2? anion, also with square-planar coordinated Se(+II), is observed. The average terminal and bridging Se? Cl bond distances are 2.273 and 2.680 Å, respectively. From redox reactions of elemental Se with boranate/thiolate in ethanol/DMF the bis(pentaselenido)selenate(+II) anion [Se(Se₅)₂]^2? was prepared as a novel type of a mixed-valent chalcogenide. In dark-red-brown [Ph₄P]₂[Se(Se₅)₂] (space group P2₁/n, a = 12.748(4), b = 14.659(5), c = 14.036(5) Å, β = 108.53(3)° at 140 K) centrosymmetric molecular [Se(Se₅)₂]^2? anions with square-planar coordination of the central Se(+II) by two bidentate pentaselenide ligands is observed (mean Se? Se bond lengths: 2.658 Å at Se(+II), 2.322 Å in [Se₅]_2?). The resulting six-membered chelate rings with chair conformation are spirocyclically linked through the central Se(+II). The vibrational spectra of the new anions are reported.     

Syntheses,Structures, and Properties of New Quaternary Gold-Chalcogenides: K2Au2Ge2S6, K2Au2Sn2Se6, and Cs2Au2SnS4

The new compounds K₂Au₂Ge₂S₆ ( 1 ), K₂Au₂Sn₂Se₆ ( 2 ), and Cs₂Au₂SnS₄ ( 3 ) have been synthesized through direct reaction of the elements with a molten polyalkalithiogermanate(stannate) flux at 650, 550, and 400 °C, respectively. Their crystal structures have been determined by single crystal X-ray diffraction techniques. 1 crystallizes in the monoclinic space group P2₁/n with a = 10.633(2) Å, b = 11.127(2) Å, c = 11.303(2) Å, β = 115,37(3)°, V = 1208,2(3) ų and Z = 4, final R(Rw) = 0.045(0.106). 2 crystallizes in the tetragonal space group P4/mcc with a = 8.251(1) Å, c = 19.961(4) Å, V = 1358,9(4) ų and Z = 4, final R(Rw) = 0.040(0.076). 3 crystallizes in the orthorhombic space group Fddd with a = 6.143(1) Å, b = 14.296(3) Å, c = 24.578(5) Å, V = 2158.4(7) ų and Z = 4, final R(Rw) = 0.039(0.095). The structures of 1 , 2 , and 3 consist of infinite, one-dimensional anionic chains containing X₂Q₆^4– units linked by Au⁺ ions and charge balancing K⁺/Cs⁺ ions situated between the chains. All compounds were investigated with differential thermal analysis, FT-IR, and solid state UV/VIS diffuse reflectance spectroscopy.     

Darstellung und Kristallstruktur von Na2Sn2Se5 Ein neues Chalkogenostannat(IV) mit schichtförmigen Komplexanionen

Preparation and Crystal Structure of Na₂Sn₂Se₅ A Novel Chalcogenostannate(IV) with Layered Complex Anions Na₂Sn₂Se₅ was obtained from a stoichiometric mixture of Na₂Se, Sn, and Se powders through a solid state reaction at 450 °C. It crystallizes orthorhombic, space group Pbca with a = 13.952(6) Å, b = 12.602(2) Å, c = 11.524(2) Å; Z = 8 and undergoes peritectic decomposition at 471(2) °C. The crystal structure was determined at ambient temperature from diffractometer data (MoKα‐radiation) and refined to a conventional R of 0.040 (1490 F_o's, 83 variables). Na₂Sn₂Se₅ is characterized by layered complex anions running parallel to (100) which are built up by SnSe₄ tetrahedra sharing common corners. The mean Sn–Se bond length calculates as 2.252(2) Å. The Na⁺ cations are coordinated to 6 or 7 Se in irregular configurations. The crystal structure can be described as a stacking of distorted c. p. 3⁶ chalcogen layers and mixed square 4⁴ alkali‐chalcogen layers.     

Syntheses,Crystal Structures,Optical and Thermal Properties of Two New Zirconium Polyselenides (K8Zr6Se30) Containing One‐dimensional Anionic Chains

Two new ternary compounds with composition K₈Zr₆Se₃₀ were prepared by reacting zirconium powder in potassium polyselenide melts. Both compounds crystallize in the triclinic space group P1 with a = 12.391(1) Å, b = 14.897(2) Å, c = 15.253(2) Å, α = 73.149(9)°, β = 76.330(9)°, γ = 70.023(9)° and V = 2502.8(3) ų for I and a = 12.2793(8) Å, b = 14.887(1) Å, c = 22.512(2) Å, α = 72.714(7)°, β = 88.475(7)°, γ = 70.748(7)° and V = 3698.1(4) ų for II . Their structures consist of infinite linear one‐dimensional anionic chains running parallel to [110], which are connected by the potassium cations. The structural differences between both compounds originate from some disordering in one of the two crystallographically independent anionic chains of each compound, in which Se^2– anions are exchanged by Se₂^2– anions to some degree. The optical band gap was determined by UV/Vis reflectance spectra to 1.91 eV for I and 1.81 eV for II . Differential scanning calorimetry investigations show, that II decomposes reversibly at about 500 °C to K₂Se₃ and ZrSe₃. On cooling II is formed again. These results are confirmed by the direct reaction between K₂Se₃ and ZrSe₃ which leads directly to II .     

The Synthesis and Crystal Structure of NpSe3

Neptunium triselenide, NpSe₃, was synthesized in high yield by the reaction of the elements in a Sb₂Se₃ flux at 1223 K. Its structure has been determined by single‐crystal X‐ray diffraction methods. Thecompound crystallizes with two formula units in space group C$\rm^{2}_{2h}$ –P2₁/mof the monoclinic system in the TiS₃ structure type with cell constants at 100 K of a = 5.592(3) Å, b = 4.002(2) Å, c = 9.422(5) Å,β = 97.40(1) °. The asymmetric unit comprises one neptunium and three selenium atoms, each with site symmetry m. Np–Se interatomic distances range from 2.859(2) to 2.927(3) Å; the Se–Se bond length of 2.340(3) Å is typical of a single bond. The compound may thus be charge‐balanced and formulated as Np⁴⁺Se^2–Se₂^2–.     

Direct Syntheses of Bis(tetraphenylphosphonium) and Bis(ethyltriphenylphosphonium) Hexabromo‐diselenates(II), [PPh4]2[Se2Br6] and [PEtPh3]2[Se2Br6]. The Crystal Structure of [PEtPh3]2[Se2Br6]

Brown crystals of [PPh₄]₂[Se₂Br₆] ( 1 ) and [PEtPh₃]₂[Se₂Br₆] ( 2 ) were obtained when selenium and bromine reacted in acetonitrile solution in the presence of tetraphenylphosphonium bromide and ethyltriphenylphosphonium bromide, respectively. The crystal structure of 2 has been determined by X‐ray methods and refined to R = 0.0420 for 4161 reflections. The crystals are monoclinic, space group P2₁/n with Z = 2 and a = 13.055(3) Å, b = 12.628(3) Å, c = 13.530(3) Å, β = 92.40(3)° (293(2) K). In the solid state structure of 2 the dinuclear hexabromo‐diselenate(II) anion is centrosymmetric and consists of two distorted almost square‐planar SeBr₄ units sharing a common edge through two bridging Br atoms. The terminal Se^II–Br bond distances are found to be 2.419(1) and 2.445(1) Å, the bridging μBr–Se^II bond distances 2.901(1) and 2.802(1) Å.     

Nb2Se2I6: Eine neue Strukturvariante bei Niobchalkogenidhalogeniden mit Kettenstruktur

Nb₂Se₂I₆: A New Structural Variation of Niobium Chalcogenide Halides with Chain Structure Single crystals of Nb₂Se₂I₆, exhibiting a metallic lustre, (monoclinic, C2/c; a = 7.110(1), b = 13.899(3), c = 13.688(3) Å, β = 99.58(3)°; Z = 8) have been obtained by heating mixture of the elements (molar ratio Nb : Se : I = 3 : 1 : 7) in evacuated sealed fused silica tubes at 1073 K for two weeks. After rapid quenching, the tube was reheated to 773 K and then cooled at a rate of 2 K h^–1. Crystals of the title compound formed at the colder part of the tube besides higher niobium iodides. Nb₂Se₂I₆ can also be obtained by slow cooling of a stoichiometric mixture of the elements from 1073 K as a minor product besides triclinic NbSe₂I₂ [1]. The crystal structure is built up with one-dimensional infinite chains [Nb₂Se₂I₄I_4/2]. The main structural features are a short Nb–Nb distance (2.903(1) Å) and a short Se–Se distance (2.318(2) Å) which is expected for +4 and –1 oxidation states, respectively. Homeotypic phases with Nb₂Y₂X₆ chains (Y = Se, Te; X = Br, I) are known [2] except for the combination Y = Se, X = I. They show a primitive rod packing of the Nb₂Y₂X₆ chains in contrast to the title compound which shows a centered rod packing.     

Cs4BiAs3Se7: A Novel Bismuth‐Selenoarsenate with Infinite [BiAs3Se7]4– Chains Containing Two Different Anions, [AsSe3]3– and trans‐[As2Se4]4–

A new phase has been prepared by methanolothermal reaction of Cs₂CO₃, BiCl₃ and Li₃AsSe₃ at 130 °C for 36 hours. Cs₄BiAs₃Se₇ ( I ) reveals the first Bi‐selenoarsenate polyanionic chain [Bi(As₂Se₄)(AsSe₃)]^4–, consisting of Bi³⁺ ions in a distorted octahedral environment of [AsSe₃]^3– and trans‐[As₂Se₄]^4– units. The latter anion consists of a central “As₂⁴⁺” dumb‐bell whereby two Se atoms are attached to each of the As atoms. Structural Data: Space Group P2₁/n, a = 13.404(4) Å, b = 23.745(8) Å, c = 13.880(4) Å, β = 99.324(6)°, Z = 8.     

On Polychalcogenides of Thallium with M2 Q11 Groups as a Structural Building Block. II. Tl4Ta2Se11: Synthesis,Crystal Structure,Properties and Spectroscopic Investigations of the First Polyselenide being Composed of a Discrete [Ta2Se11]4— Anion

The new ternary compound Tl₄Ta₂Se₁₁ was prepared in a melt of thallium polyselenides applying elemental tantalum. It crystallises in the triclinic space group P1¯ with a = 7.996(1) Å, b = 9.866(1) Å, c = 13.668(2) Å, α = 73.03(1)°, β = 89.21(2)° and γ = 85.72(1)°. Tl₄Ta₂Se₁₁ is the first polyselenide with discrete complex [M₂Se₁₁]^4— anions. Every Ta atom is in a sevenfold environment of Se atoms to form a distorted pentagonal bi‐pyramid. The two TaSe₇ polyhedra have a face in common thus yielding the [Ta₂Se₁₁]^4— unit. In the structure, the anions are well separated by the Tl¹⁺ cations. An assignment of the different vibration modes in the IR and Raman spectra is given based on density functional calculations.     

One‐Dimensional Zinc Selenophosphates: A2ZnP2Se6 (A = K,Rb, Cs)

The new compounds A₂ZnP₂Se₆ (A = K, Rb, Cs) were synthesized via molten salt flux syntheses. The crystals feature one‐dimensional ¹/_∞[ZnP₂Se₆]^2– chains charge balanced by alkali metal ions between the chains. K₂ZnP₂Se₆ crystallizes in the monoclinic space group P2₁/c; cell parameters a = 12.537(3) Å, b = 7.2742(14) Å, c = 14.164(3) Å, β = 109.63(3)°, Z = 4, and V = 1216.7(4) ų. Rb₂ZnP₂Se₆ and Cs₂ZnP₂Se₆ are isotypic, crystallizing in the triclinic space group P$\bar{1}$ . Rb₂ZnP₂Se₆ has cell parameters of a = 7.4944(15) Å, b = 7.6013(15) Å, c = 12.729(3) Å, α = 96.57(3)°, β = 105.52(3)°, γ = 110.54(3)°, Z = 2, and V = 636.6(2) ų. Cs₂ZnP₂Se₆ has cell parameters of a = 7.6543(6) Å, b = 7.7006(6) Å, c = 12.7373(11) Å, α = 97.007(7)°, β = 104.335(7)°, γ = 109.241(6)°, Z = 2, and V = 669.54(10) ų.     

Synthesis,Structural, and Optical Characterization of a New Europium(II) Tin Selenide,Eu8(Sn4Se14)(Se3)2 with a (Sn4Se14)12– Building Block

A new phase in europium‐tin‐chalcogenide chemistry has been prepared using the reactive flux method: Eu₈(Sn₄Se₁₄)(Se₃)₂. The compound crystallizes in the orthorhombic space group P2₁2₁2 with cell parameters a = 11.990(2) Å, b = 16.425(4) Å, c = 8.543(1) Å, and Z = 2. Eu₈(Sn₄Se₁₄)(Se₃)₂ is a three dimensional structure with Eu^II cations linked together with an unusual (Sn₄Se₁₄)^12– anionic unit and (Se₃)^2– chains. UV‐VIS‐NIR band‐gap analysis shows that these black metallic crystals are likely semiconductors with an optical band‐gap of 1.07 eV.     

Two New Quaternary Thiophosphates with Pseudo One‐dimensional Structures: Syntheses and Crystal Structures of Cs3Sm[PS4]2 and Rb3Sm[PS4]2

The new thiophosphates Rb₃Sm[PS₄]₂ and Cs₃Sm[PS₄]₂ were obtained as pale yellow needles using an in‐situ formed thiophosphate flux. Rb₃Sm[PS₄]₂ crystallizes in the space group P2₁ with a = 9.7061(19) Å, b = 6.7517(14) Å, c = 11.395(2) Å, β = 90.63(3)°, (Z = 2); Cs₃Sm[PS₄]₂ in space group P2₁/n with a = 15.311(3) Å, b = 6.8762(14) Å, c = 15.352(3) Å, β = 99.49(3)°, (Z = 4). The crystal structures are characterized by the formation of complex anionic chains, which run along the [010] direction in both structures. One of the two independent thiophosphate groups connects three Sm³⁺ cations to form an infinite zigzag like arrangement, while the other acts as a terminal ligand to one Sm³⁺ions. Such a μ₃ or face‐grafting coordination mode of a [PS₄]³⁻ anion is not very common. The Sm³⁺ ions are in bicapped trigonal prismatic chalcogen coordination. The average Sm–S distances within the trigonal prisms are close to 2.88Å, while the bonds to the capping atoms are distinctly longer. The chains are chiral yet their symmetry is close to 2₁/m. In contrast to the rubidium compound, Cs₃Sm[PS₄]₂ contains both enantiomorphs. In both structures the chains are arranged as a distorted hexagonal rod packing.     

Selenoarsenate aus wäßriger Lösung. Die Kristallstruktur von Na3AsO3Se · 12 H2O und Na3AsSe4 · 9H2O

Selenoarsenates from Aqueous Solutions. Crystal Structures of Na₃AsO₃Se · 12 H₂O and Na₃AsSe₄ · 9 H₂O Selenoarsenates are obtained from aqueous solutions as colourless hydrated salts by reactions either of As₂O₃ with NaOH and selenium or of Na₂Se with As₂Se₃ and selenium under strictly anaerobic conditions. Besides of tetrahedral anions AsO₃Se³⁻ and AsSe₄³⁻, extensive hydrogen bridge systems with rather strong O H …︁s Se bonds determine the structures. Na₃AsO₃Se · 12 H₂O is orthorhombic (P2₁2₁2₁) with a = 9.220(3), b = 13.018(3), c = 14.048(4) Å, Z = 4. Cubic Na₃AsSe₄ ·s 9H₂O (P2₁3) with a = 12.149(3) Å is isotypic to Schlippe's salt, Na₃SbS₄ · 9 H₂O. The full X-ray structure analyses from four-circle diffractometer data show the selenium atoms of the AsO₃Se³⁻ and AsSe₄³⁻ anions to be H-acceptors in six Se …︁ H O hydrogen bridges with d(Se …︁ O) = 3.357–3.693 Å and d(Se …︁ H) = 2.47–2.89 Å. The As Se bond in AsO₃Se³⁻ (2.283 Å) is shorter than in AsSe₄³⁻ (2.319 Å).     

Na2B2Se7, K2B2S7 und K2B2Se7: Drei Perchalkogenoborate mit neuem polymeren Anionengerüst

Na₂B₂Se₇, K₂B₂S₇, and K₂B₂Se₇: Three Perchalcogenoborates with a Novel Polymeric Anion Network Na₂B₂Se₇ (I 2/a; a = 11.863(4) Å, b = 6.703(2) Å, c = 13.811(6) Å, β = 109.41(2)°; Z = 4), K₂B₂S₇ (I 2/a; a = 11.660(2) Å, β = 6.827(1) Å, c = 12.992(3) Å, β = 106.78(3)°; Z = 4), and K₂B₂Se₇ (I 2/a; a = 12.092(4) Å, b = 7.054(2) Å, c = 13.991(5) Å, β = 107.79(3)°; Z = 4) were prepared by reaction of stoichiometric amounts of sodium selenide (potassium sulfide) with boron and sulfur or of potassium selenide and boron diselenide, respectively, at 600°C with subsequent annealing. The crystal structures consist of polymeric anion chains of composition ([B₂S₇]^2?)_n or ([B₂Se₇]^2?)_n formed by spirocyclically connected five-membered B₂S₃ (B₂Se₃) rings and six-membered B₂S₄ (B₂Se₄) rings. The nine-coordinate alkaline metal cations are situated in between.     

New hydrogen-bonded dimeric and polymeric gold(I) complexes of the heterodifunctional ligand Ph2PNHP(O)Ph2

The preparation of several new gold(I) complexes by chloride metathesis of [AuCl(HL)] [HL=Ph₂PNHP(O)Ph₂] with either HL or K[Ph₂P(E)NP(E)Ph₂] (E=S or Se) is described. All compounds were characterised by a combination of ³¹P{¹H}, ¹H and IR spectroscopy, microanalysis and X-ray crystallography. X-ray structural studies reveal that [Au(HL)₂]Cl [monoclinic, space group P2₁/c, a=9.0726(3) Å, b=21.0847(6) Å, c=12.0131(3) Å, β=105.1090(10)°, V=2219 ų, Z=2, final R=3.97] forms a one dimensional polymeric structure in which alternating [Au(HL)₂]⁺ and Cl⁻ ions are linked through intermolecular N–H⋯Cl hydrogen-bonding. In contrast the three-co-ordinate compound [Au{Ph₂P(Se)NP(Se)Ph₂-Se,Se′}(HL)] [monoclinic, space group P2₁/a, a=21.6752(5) Å, b=9.1200(10) Å, c=24.0742(7) Å, β=106.080(2)°, V=4573 ų, Z=4, final R=8.94] forms hydrogen-bonded dimer pairs analogous to that previously observed in non-complexed HL. The X-ray crystal structure of the gold(I) precursor [AuCl(HL)] has also been determined: monoclinic, space group P2₁/c, a=10.217(8) Å, b=23.256(5) Å, c=20.086(5) Å, β=101.15(4)°, V=4683 ų, Z=8, final R=5.2. The X-ray crystal structure reveals intermolecular N–H⋯OP hydrogen-bonding between adjacent [AuCl(HL)] molecules forming infinite chains.     

Piaselenol—Piaselenolium—Pentaiodid (C6H4N2Se · C6H5N2Se+I3− · I2), eine Struktur mit Polyiodid-schichten

Piaselenole—Piaselenolium—Pentaiodide (C₆H₄N₂Se · C₆H₅N₂Se⁺ I₃^? · I₂), a Structure with Polyiodide Layers The title compound crystallizes in the monoclinic space group P2₁/n with a = 9.320(3), b = 13.812(2), c = 17.159(3) Å, β = 96.11(2)°, V = 2196.3 ų, Z = 4. There occur no isolated I^5? anions but layer-shaped polyiodide aggregates built up by linear, asymmetric I₃^? anions and I₂ molecules. Almost linear triiodide chains are connected by I₂ molecules in a novel type of arrangement to form slightly puckered layers. The polyiodide layers contain several substructures known from other examples. The piaselenole and its conjugated acid, the piaselenolium cation, form a ribbon-like quasi-polymer in which the two components are alternating. They are connected in turns by a linear NH? N hydrogen bridge (N? N: 2.844 Å) and by a so called (SeN)₂-connectivity parallelogram, in which Se? N bonds and Se? N contacts are adjacent. Here we found a very short Se? N contact distance of 2.691 Å. The bond distances of piaselenole (Se? N: 1.787(3) Å, N? C: 1.318(5) Å, C? C: 1.453(8) Å) and also the angles are equal or similar to those occuring in other 1,2,5-selenadiazoles. The protonation of one N in the SeN₂ unit results in a loss of symmetry and significant changes in bonding distances and angles.     

Synthesis and Crystal Structure of Bis(tetraethylammonium) Octabromo‐triselenate(II)‐{dibromodiselenate(I)}, [NEt4]2[Se3Br8(Se2Br2)], the Salt of a Mixed‐valence Bromoselenate(II,I) Anion

The brown crystals of [NEt₄]₂[Se₃Br₈(Se₂Br₂)] ( 1 ) were obtained when selenium and bromine reacted in the solution of acetonitrile in the presence of tetraethylammonium bromide. The crystal structure of 1 has been determined by the X‐ray methods and refined to R = 0.0308 for 10433 reflections. The crystals are monoclinic, space group P2₁ with Z = 2 and a = 12.0393(3) Å, b = 11.8746(3) Å, c = 13.1946(3) Å, β = 96.561(1)° (123 K). In the solid state structure the anion of 1 is built up of Se₃Br₈ unit which consists of a triangular arrangement of three planar SeBr₄ units sharing a common edge through two μ₃‐bridging Br atoms, and one Se₂Br₂ molecule which is linked to one of μ₃‐bridging Br atoms. The three Se^II atoms form a triangle which is almost perpendicular to the planes given by three SeBr₄ moieties. The contact between the μ₃Br and the Se^I atom of the Se₂Br₂ molecule is 3.1711(8) Å and can be interpreted as a bond of the donor‐acceptor type with the μ₃Br as donor and the Se₂Br₂ molecule as acceptor. The terminal Se^II‐Br and μ₃Br‐Se^II bond lengths are in the ranges 2.3537(7)–2.4737(7) Å and 2.7628(7)–3.1701(7) Å, respectively. The bond lengths in coordinated Se₂Br₂ molecule are: Se^I‐Se^I = 2.2636(9) Å, Se^I‐Br = 2.3387(11) and 2.3936(8) Å.     

Synthesis and Crystal Structure of Bis(tetraphenylphosphonium) Hexabromo‐diselenate(II)‐bis{dibromodiselenate(I)}, [PPh4]2[Se2Br6(Se2Br2)2], the Salt of a Mixed‐valence Bromoselenate(II,I) Anion

The Red crystals of [PPh₄]₂[Se₂Br₆(Se₂Br₂)₂] ( 1 ) were obtained when selenium and bromine reacted in the solution of acetonitrile in the presence of tetraphenylphosphonium bromide. The crystal structure of 1 has been determined by X‐ray diffraction and refined to R = 0.0201 for 4024 reflections. The crystals are triclinic, space group with Z = 2 and a = 11.2757(4) Å, b = 12.3347(5) Å, c = 12.4948(5) Å, α = 113.152(4)°, β = 114.745(4)°, γ = 91.208(3)° (120(2) K). In the solid state the anion of 1 is built up of the Se₂Br₆ core and two Se₂Br₂ molecules each of which is linked to one of the trans‐positioned terminal Br_t atoms of the Se₂Br₆ core. The central Se₂Br₆ part consists of a nearly planar arrangement of two planar SeBr₄ units sharing a common edge through two μ₂‐bridging Br atoms. The contact between the Br_t and the Se^I atom of the Se₂Br₂ molecule is 3.0872(5) Å and can be interpreted as a bond of the donor‐acceptor type with the Br_t as donor and the Se₂Br₂ molecule as acceptor. The terminal Se^II–Br and μ₂Br–Se^II bond lengths are 2.3654(4), 2.6699(5) Å and 2.5482(5), 3.0265(5) Å, respectively. The bond lengths in the coordinated Se₂Br₂ molecule are: Se^I–Se^I = 2.2686(5) Å, Se^I–Br = 2.3779(5) and 2.3810(5) Å.