Unsaturated five-membered selenium-silicon containing heterocycles based on the reactions of selenium di- and tetrahalides with diorganyl diethynyl silanes

Reactions of SeBr₂ and SeCl₂ with diorganyl diethynyl silanes RR¹Si(CCH)₂ in CHCl₃ at room temperature result in regio- and stereoselective formation of a new class of unsaturated five-membered heterocycles, 4,4-R,R¹-3,6-dichloro(dibromo)-1,4-selenasilafulvenes (Z-isomers predominately), in preparative yields. Under similar conditions the reaction of SeBr₄ and SeCl₄ with diorganyl diethynyl silanes RR¹Si(CCH)₂ proceeds regioselectively to afford another new class of unsaturated five-membered heterocycles, 2-dichloro(dibromo)-methyl-2,4-dichloro(dibromo)-3,3-diorganyl-1-selena-3-silacyclopentenes-4. The structures of the heterocycles were proved by multinuclear (¹H, ¹³C, ²⁹Si, ⁷⁷Se) NMR spectroscopy, 2D NOESY NMR spectroscopy and mass-spectrometry. A long-range spin-spin interaction of protons through five bonds lacking in E-isomers was revealed in Z-isomers of fulvene-type heterocycles. In the MS spectra heterocycles of cyclopentene structure were shown to manifest themselves as fragmentary ions [M−HX]⁺ or [M−X]⁺.     

Electrophilic addition of selenium and telluriom halides to methyldiethynylsilane

Regio- and stereoselective electrophilic addition reactions of SeCl₂, SeBr₂, SeCl₄, SeBr₄ to methyldiethynylsilane lead to predominant formation of the Z-isomers of 3,6-dihalo-4-methyl-1,4-selenasilafulvenes, disiloxanes on their bases, as well as disiloxanes formed upon the reaction with methyldiethynylsilane. TeCl₄ reacts with methyldiethynylsilane with predominant formation of the E-isomer of 1,1,3,6-tetrachloro-1-methyl-1-(methyldiethynylsiloxy)-1,4-tellura(IV)silafulvene as a result of the reaction of the intermediate E-isomer of 4-methyl-1,1,3,6-tetrachloro-1,4-tellura(IV)silafulvene with methyldiethynylsilane. The structure of the products was proved by the methods of ¹H, ⁷⁷Se NMR, IR spectroscopy and chromatomass spectrometry.     

4,4-Diorganyl-1,1,3,6-tetrachloro-1,4-tellura(IV)silafulvenes - New class of tellurium-silicon containing heterocycles

The reaction of TeCl₄ with diorganyl diethynyl silanes RR¹Si(CCH)₂ in CHCl₃ at room temperature leads to regio- and stereoselective formation of a new class of unsaturated five-membered heterocycles, 4,4-diorganyl-1,1,3,6-tetrachloro-1,4-tellura(IV)silafulvenes, in high yields. In the case of dialkyl substituents at the silicon atom the reaction proceeds with 100% stereoselectively to afford only E-isomers, while for cyclic diethynyl silanes the spiro-heterocycles formed have Z- and E-configurations, E-isomers being the predominant ones. Structures of the heterocycles have been proved by the multinuclear (¹H, ¹³C, ²⁹Si, ¹²⁵Te) NMR spectroscopy, 2D NOESY NMR spectroscopy and mass-spectrometry. Z-Isomers are characterized by a long-range spin-spin interaction of protons through five bonds with ⁵J_HH 0.2-0.5 Hz lacking in E-isomers. In the mass spectra the heterocycles manifest themselves as the fragment ions [M−Cl₂]⁺.     

Unsaturated five-membered selenium–germanium containing heterocycles based on the reactions of selenium di- and tetrahalides with diorganyl diethynyl germanes

Regio- and stereoselective reactions of selenium dihalides with diorganyl diethynyl germanes in CHCl₃ afford in yields from preparative to quantitative the first representatives of a new class of selenium–germanium containing heterocycles - 3,6-dihalogen-4,4-diorganyl-1,4-selenagermafulvenes. The reaction of selenium tetrachloride under the same conditions leads to the first representatives of a new class of selenium–germanium containing cyclopentene heterocycles - 2-dichloromethyl-2,4-dichloro-3,3-diorganyl-1-selena-3-germacyclopentenes-4 as well as to the unknown 3,6,6-trichloro-4,4-dialkyl-1,4-selenagermafulvenes formed as a result of a spontaneous dehydrochlorination of the cyclopentene heterocycles. In a case of SeBr₄ the process of dehydrobromination is dominating. The structures of the heterocycles were proved by multinuclear (¹H, ¹³C, ⁷⁷Se) spectroscopy and mass-spectrometry. In the ¹H NMR spectra of Z-isomers of 1,4-selenagermafulvenes a long-range spin–spin interaction between exo- and endocyclic olefinic protons through five bonds is revealed lacking in the E-isomers.     

Synthesis and Crystal Structure of >Bis(tetrapropylammonium) Hexabromotellurate(IV)‐bis{dibromoselenate(II)}, [NnPr4]2[TeBr6(SeBr2)2], the Salt of a Mixed‐valence Bromotellurate(IV)‐Selenate(II) Anion

Dark brown crystals of [NⁿPr₄]₂[TeBr₆(SeBr₂)₂] ( 1 ) were obtained when selenium and bromine (1:1) were allowed to react in acetonitrile solution in the presence of tellurium(IV) bromide and tetrapropylammonium bromide. The salt 1 crystallizes in the monoclinic space group P2₁/n with the cell dimensions a = 14.7870(3) Å, b = 9.5523(3) Å, c = 16.7325(3) Å, β = 110.56(10)° (at 123(2) K). In the solid state the [TeBr₆(SeBr₂)₂]^2– anion contains a nearly regular [TeBr₆] octahedron in which the four equatorial bromo ligands have developed bonds to Se^II atoms of the SeBr₂ molecules. The contacts between the bridging bromo and the Se^II atoms of the SeBr₂ molecules are 3.0000(4) and 3.0561(4) Å, and can be interpreted as bonds of the donor‐acceptor type with the bridging bromo ligands as donors and the SeBr₂ molecules as acceptors. The Te^IV–Br distances are in the range 2.6816(3)–2.7131(3) Å and the Se^II–Br bond lengths in the coordinated SeBr₂ molecules are 2.3548(4) and 2.3725(4) Å.     

Reaction of Selenium with Bromine in the Presence of Methyltriphenylphosphonium Bromide: Syntheses and Crystal Structures of [PMePh3]2[Se2Br6] and [PMePh3]2[SeBr6(SeBr2)2]

The brown crystals of [PMePh₃]₂[Se₂Br₆] ( 1 ) and red crystals of [PMePh₃]₂[SeBr₆(SeBr₂)₂] ( 2 ) were obtained when selenium and bromine reacted in the solution of acetonitrile in the presence of methyltriphenylphosphonium bromide. The crystal structures of 1 and 2 has been determined by the X‐ray methods and refined to R = 0.0373 for 2397 reflections and 0.0397 for 3417 reflections, respectively. The salt 1 crystallizes in the monoclinic space group P2₁/n with the cell dimensions a = 13.202(5) Å, b = 11.954(4) Å, c = 13.418(6) Å, β = 93.08(4)° (193(2)). The crystals of 2 are triclinic, space group with the cell dimensions a = 10.266(3) Å, b = 11.311(3) Å, c = 11.619(2) Å, α = 108.87(2)°, β = 105.72(2)°, γ = 99.40(2)° (193(2) K). In the solid state structure of 1 the dinuclear hexabromo‐diselenate(II) anion is centrosymmetric and consists of two distorted almost square planar SeBr₄ units sharing a common edge through two μ‐bridging Br atoms. The terminal Se^II–Br bonds are 2.3984(11) and 2.4273(11) Å, whereas the bridging μBr–Se^II bonds are 2.7817(11) and 2.9081(12) Å. In the solid state the trinuclear [SeBr₆(SeBr₂)₂]^2? anion of 2 is centrosymmetric too and contains a nearly regular [SeBr₆] octahedron where the four equatorial bromo ligands each have developed bonds to the Se^II atoms of the SeBr₂ molecules. The contacts between the bridging bromo and the Se^II atoms of the SeBr₂ molecules are 3.0603(15) and 3.1043(12) Å, and can be interpreted as bonds of the donor‐acceptor type with the bridging bromo ligands as donors and the SeBr₂ molecules as acceptors. The Se^IV–Br distances are in the range 2.5570(9)–2.5773(11) Å and the Se^II–Br bond lengths in coordinated SeBr₂ molecules – 2.3411(12) and 2.3421(10) Å.     

Siloles and Acetenyl Aromatics Copolymers: Synthesis,Characterization and Photophysical Properties

Two copolymers, poly(1,1‐dimethyl‐3,4‐diphenylsilole‐alt‐N‐hexyl‐3,6‐diethynylcarbazole) (PS‐DyCz) and poly(1,1‐dimethyl‐3,4‐diphenylsilole‐alt‐2,7‐diethynyl‐9,9′‐dihexylfluorene) (PS‐DyF), were synthesized by Sonogashira coupling reaction of 2,5‐dibromo‐1,1‐dimethyl‐3,4‐diphenylsilole and N‐hexyl‐3,6‐diethynylcarbazole or 2,7‐diethynyl‐9,9′‐dihexylfluorene, respectively. The chemical structures of the copolymers were characterized by NMR, FT‐IR techniques. Their thermal and photophysical properties were evaluated by TGA, DSC, UV‐Vis and fluorescence spectroscopy, respectively. The weight‐averaged molecular weights (M_w) of PS‐DyCz and PS‐DyF are 1.20×10⁴ and 3.83×10⁴ Da, respectively. The degree of polymerization is 8 and 22 units. These π‐conjugated polymers exhibited lower band‐gap of 2.25 and 2.70 eV due to the presence of silole rings and C?C triple bonds in their backbone, the results were consistent with the density functional (DFT) calculations at the B3LYP/6‐31G* level.     

Synthesis and Crystal Structure of Tetrakis(tetramethylammonium) Bis[decabromotetraselenate(II)]‐bis[dibromodiselenate(I)], [(CH3)4N]4[(Se4Br10)2(Se2Br2)2], the Salt of a Mixed‐Valence Bromoselenate(II/I) Anion

Brown crystals of [NMe₄]₄[(Se₄Br₁₀)₂(Se₂Br₂)₂] ( 1 ) were obtained from the reaction of selenium and bromine in acetonitrile in the presence of tetramethylammonium bromide. The crystal structure of 1 was determined by X‐ray diffraction and refined to R = 0.0297 for 8401 reflections. The crystals are monoclinic, space group P2₁/c with Z = 4 and a = 12.646(3) Å, b = 16.499(3) Å, c = 16.844(3) Å, β = 101.70(3)° (123 K). In the solid‐state structure, the anion of 1 is built up of two [Se₄Br₁₀]^2– ions. Each shows a triangular arrangement of three planar SeBr₄ units sharing a common edge through two μ₃‐bridging bromine atoms, and one SeBr₂ molecule, which is linked to the Se^II atoms of two SeBr₄ units; between the Se₄Br₁₀^2– ions a dimerized Se₂Br₂ molecule (Se₄Br₄) is situated and one Se^I atom of each Se₂Br₂ molecule has two weak contacts [3.3514(14) Å and 3.3952(11) Å] to two bromine atoms of one SeBr₄ unit. Four Se^I atoms of a dimerized Se₂Br₂ molecule are in a almost regular planar tetraangular arrangement. Contacts between the Se^II atom of the SeBr₂ molecule and the Se^II atoms of two SeBr₄ units are 3.035(1) Å and 3.115(1) Å, and can be interpreted as donor‐acceptor type bonds with the Se^II atoms of SeBr₄ units as donors and the SeBr₂ molecule as acceptor. The terminal Se^II–Br and μ₃‐Br–Se^II bond lengths are in the ranges 2.3376(10) to 2.4384(8) Å and 2.8036(9) to 3.3183(13) Å, respectively. The bond lengths in the dimerized Se₂Br₂ molecule are: Se^I–Se^I = 2.2945(8) Å and 3.1398(12), Se^I–Br = 2.3659(11) and 2.3689(10) Å.     

Structure and Bonding in Bis(1‐naphthyl) Diselenide and Bis{[2‐(N,N‐dimethylamino)methyl]phenyl} Tetraselenide,and Their Brominated Derivatives

The formation and crystal structures of bis(1‐naphthyl) diselenide ( 1 ) and bis{[2‐(N,N‐dimethylamino)methyl]phenyl} tetraselenide ( 2 ) are described. Whereas 1 can be produced in good yields, 2 is formed only as a minor product together with the known main product, bis{[2‐(N,N‐dimethylamino)methyl]phenyl} diselenide. The composition of the reaction mixture is semi‐quantitatively estimated by ⁷⁷Se NMR spectroscopy and DFT calculations. The effect of the n²→σ*(Se–Se) and π→σ*(Se–Se) secondary bonding interactions on the Se–Se bonds is discussed both by DFT calculations and comparison with literature, as available. The bromination of 1 yields monomeric (1‐naphthyl)selenenyl bromide ( 3 ) in good yields. That of the reaction mixture of (C₆H₄CH₂NMe₂)Se_x (x = 2–4) and Se₈ afforded (C₆H₄CH₂NMe₂H)₂[SeBr₄] ( 4 ) and (C₆H₄CH₂NMe₂H)₂[SeBr₆] ( 5 ) in addition to (C₆H₄CH₂NMe₂)SeBr, which has been previously reported.     

Synthesis of a 2-benzocymantrenylpyridine and further mechanistic insights

The synthesis of a new benzocymantrene derivative containing an appended pyridyl moiety was attempted by reacting a lithioindenylpyridine with (CO)₅MnBr. The reaction led to the formation of small amounts of the targeted benzocymantrene, which was subsequently characterized by structural X-ray diffraction analysis. Alternative treatment of the same ligand with (η¹-benzyl)pentacarbonylmanganese led to the formation of a five-membered manganacycle resulting from the C-H bond activation at the five-membered ring of the indenyl group. To rationalize the origin of the poor yield in the benzocymantrene derivative a complete study of the reaction profile was carried out by means of a state-of-the-art DFT-D2 method. The theory indicated that the main difficulty in producing the targeted benzocymantrene stems from the relatively high activation energy barrier necessary to convert a (η¹-indenyl)Mn(CO)₅ intermediate into a (η³-indenyl)Mn(CO)₄ transient species.     

SeBr3[AlBr4] und TeI3[AlI4] – zwei weitere Vertreter des SCl3[AlCl4]-Strukturtyps

SeBr₃[AlBr₄] and TeI₃[AlI₄] – two further Compounds in the SCl₃[AlCl₄] Structure Type The reaction of SeBr₄ and AlBr₃ in a closed glass ampoule at 150°C yields quantitatively SeBr₃[AlBr₄] in form of yellow moisture sensitive crystals. From Te, two equivalents of I₂, and AlI₃ one obtains TeI₃[AlI₄] in form of dark red, moisture sensitive crystals. Both compounds crystallize monoclinic in the space group Pc (SeBr₃[AlBr₄]: a = 670.7(7) pm, b = 663.9(5) pm, c = 1 428.6(2) pm, β = 101.21(9)°, TeI₃[AlI₄]: a = 731.9(1) pm, b = 730.8(1) pm, c = 1 565.5(3) pm, β = 102.01(2)°). They are isotypic and have the SCl₃[AlCl₄] structure type. The structures are built of tetrahedral AlX₄^? ions and of pyramidal EX₃⁺ ions (E = S, Se, Te; X = Cl, Br, I). The chalcogen atoms are additionally coordinated by halogen atoms of surrounding AlX₄^? ions, corresponding to a strongly distorted octahedral coordination EX₃₊₃.     

Synthesis and Crystal Structure of Bis(methyltriphenylphosphonium) Hexabromotellurate(IV)‐bis{dibromoselenate(II)}, [PMePh3]2[TeBr6(SeBr2)2], the Salt of a Mixed‐valence Bromotellurate(IV)‐Selenate(II) Anion

Brown crystals of [PMePh₃]₂[TeBr₆(SeBr₂)₂] ( 1 ) were obtained when selenium and bromine (1:1) react in acetonitrile solution in the presence of tellurium(IV) bromide and methyltriphenylphosphonium bromide. The salt 1 crystallizes in the triclinic space group P1¯ with the cell dimensions a = 10.3630(14)Å, b = 11.5140(12)Å, c = 11.7605(17)Å, α = 108.643(9)°, β = 106.171(10)° and γ = 99.077(9)° (296 K). In the solid state the [TeBr₆(SeBr₂)₂]^2— anion contains a nearly regular [TeBr₆] octahedron where the four equatorial bromo ligands each have developed a bond to the Se^II atom of a SeBr₂ molecule. The contacts between the bridging bromo and the Se^II atoms of the SeBr₂ molecules are observed in the range 3.11—3.21Å, and can be interpreted as bonds of the donor‐acceptor type with the bridging bromo ligands as donors and the SeBr₂ molecules as acceptors. The Te^IV—Br distances are in the range 2.67—2.72Å, and the Se^II—Br bond lengths in coordinated SeBr₂ molecules in the range 2.33—2.34Å.     

Various silicon‐containing polymers with Si(H)?CC units

Nine new kinds of thermosetting polymers with the Si(H)? C?C unit were synthesized by dehydrogenative polycondensation reactions between hydrosilanes and diethynyl compounds in the presence of a magnesia catalyst. Phenylsilane, silane, vinylsilane, and n‐octylsilane were used as the hydrosilanes, and 1,3‐diethynylbenzene, 1,4‐diethynylbenzene, 4,4′‐diethynyldiphenyl ether, and 1,3‐diethynyl‐1,1,3,3‐tetramethyldisiloxane were used as the diethynyl compounds. All the polymers were thermosetting, highly heat‐resistant, easily soluble in a solvent, and moldable. In particular, ? Si(R)H? C?C? C₆H₄? C?C? (R = H or CH?CH₂) showed high thermal stability; the temperature of 5% weight loss was greater than 800 °C, and the residue at 1000 °C was over 90%. The thermal stabilities of the polymers were attributed to the crosslinking reaction of the Si? H and C?C bonds. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2658–2669, 2001     

Zur calorimetrischen Bestimmung der Bildungsenthalpie von SeBr4 und SeOBr2

Calorimetric Determination of the Enthalpy of Formation of SeBr₄ and SeOBr₂ It was determined the enthalpy of solution of SeO₂, SeBr₄, and SeOBr₂ in 1 N HBr and derived the enthalpies of formation. The following data basing on the enthalpy of formation for SeO₂ were obtained .     

Treatment of dimethyl (+)-L-tartrate with sulfur tetrafluoride

Treatment of dimethyl (+)-L-tartrate (I) with sulfur tetrafluoride results in the formation of an intermediate, 2-fluoro-1,2-bis(methoxycarbonyl)ethyl fluorosulfite (II), which under the action of hydrogen fluoride, present in the reaction mixture, is converted into dimethyl (?)(2S:3S)-2-fluoro-3-hydroxysuccinate (III). The reaction of the latter with SF₄ leads to dimethyl meso-2,3-difluorosuccinate (IV). The structure and configurations of the compounds obtained were established by ¹H and ¹⁹F NMR. Treatment of dimethyl (+)-L-tartrate (I) with sulfur tetrafluoride in the presence of excessive hydrogen fluoride gave dimethyl meso-2,3-difluorosuccinate in 96% yield.     

Reaction Equilibrium and Kinetics of Synthesis of Polyoxymethylene Dimethyl Ethers from Formaldehyde and Methanol

Polyoxymethylene dimethyl ethers (PODE _n ) are environmentally friendly diesel fuel additives. They belong to alkyl ethers that could reduce solid particulate matter formation and emissions of carbon monoxide and nitrogen oxide when added into diesel fuels. This work aimed to researching chemical equilibrium and reaction kinetics of the synthesis of polyoxymethylene dimethyl ethers from formaldehyde and methanol catalyzed by an ion-exchange resin at the reaction temperatures 313, 333, 343 and 353 K. In the reversible reaction, the K_{n ≥ 2}/K₂ ratio was equal to one. The reaction orders of methanol, formaldehyde, water and PODE _n were 0.2638, 0.1328, 0.1565 and 0.0048, respectively. At a 10 wt % dosage of H-SIR1 resin, the rate constants of the methylal (dimethoxymethane) formation and depolymerization were 1.04 × 10⁴ and 3.43 × 10⁶ min^–1, respectively, and the pre-exponential factor for the PODE_{n + 1} formation was 2.50 × 10³ min^–1. Activation energies for the methylal propagation and depolymerization and PODE_{n > 1} formation were 30.46, 48.40 and 27.10 kJ/mol, respectively. The results indicated that the equilibrium constants of PODE_{n > 1} formation reactions were consistent. The exothermic reaction of methylal formation was easier than the reverse reaction and more difficult than the formation of PODE_{n > 1}.     

Temperature-dependent kinetics of the simplest Criegee intermediate reaction with dimethyl sulfoxide

Criegee intermediates are thought to play roles in atmospheric chemistry, including OH radical formation, oxidation of SO₂, NO₂, etc. CH₂OO is the simplest Criegee intermediate, of which the reactivity has been a hot topic. Here we investigated the kinetics of CH₂OO reaction with dimethyl sulfoxide (DMSO) under 278–349 K and 10–150 Torr. DMSO is an important species formed in the oxidation of dimethyl sulfide in the biogenic sulfur cycle. The concentration of CH₂OO was monitored in real-time via its mid-infrared absorption band at about 1,286 cm⁻¹ (Q branch of the ν₄ band) with a high-resolution quantum cascade laser spectrometer. The 298 K bimolecular rate coefficient was determined to be k₂₉₈ = (2.3 ± 0.3) × 10⁻¹² cm³/s at 30 Torr with an Arrhenius activation energy of −3.9 ± 0.2 kcal/mol and a weak pressure dependence for pressures higher than 30 Torr (k₂₉₈ = (2.8 ± 0.3) × 10⁻¹² cm³/s at 100 Torr). The reaction is speculated to undergo a five-membered ring intermediate, analogous to that of CH₂OO with SO₂. The negative activation energy indicates that the rate-determining transition state is submerged. The magnitude of the reaction rate coefficient lies in between those of CH₂OO reactions with (CH₃)₂CO and with SO₂.     

FT‐IR kinetic and product study of the OH radical and Cl‐atom–initiated oxidation of dibasic esters

Using a relative kinetic technique, rate coefficients have been measured, at 296 ± 2 K and 740 Torr total pressure of synthetic air, for the gas‐phase reaction of OH radicals with the dibasic esters dimethyl succinate [CH₃OC(O)CH₂CH₂C(O)OCH₃], dimethyl glutarate [CH₃OC(O)CH₂CH₂CH₂C(O)OCH₃], and dimethyl adipate [CH₃OC(O)CH₂CH₂CH₂CH₂C(O)OCH₃]. The rate coefficients obtained were (in units of cm³ molecule^?1 s^?1): dimethyl succinate (1.89 ± 0.26) × 10^?12; dimethyl glutarate (2.13 ± 0.28) × 10^?12; and dimethyl adipate (3.64 ± 0.66) × 10^?12. Rate coefficients have been also measured for the reaction of chlorine atoms with the three dibasic esters; the rate coefficients obtained were (in units of cm³ molecule^?1 s^?1): dimethyl succinate (6.79 ± 0.93) × 10^?12; dimethyl glutarate (1.90 ± 0.33) × 10^?11; and dimethyl adipate (6.08 ± 0.86) × 10^?11. Dibasic esters are industrial solvents, and their increased use will lead to their possible release into the atmosphere, where they may contribute to the formation of photochemical air pollution in urban and regional areas. Consequently, the products formed from the oxidation of dimethyl succinate have been investigated in a 405‐L Pyrex glass reactor using Cl‐atom–initiated oxidation as a surrogate for the OH radical. The products observed using in situ Fourier transform infrared (FT‐IR) absorption spectroscopy and their fractional molar yields were: succinic formic anhydride (0.341 ± 0.068), monomethyl succinate (0.447 ± 0.111), carbon monoxide (0.307 ± 0.061), dimethyl oxaloacetate (0.176 ± 0.044), and methoxy formylperoxynitrate (0.032–0.084). These products account for 82.4 ± 16.4% C of the total reaction products. Although there are large uncertainties in the quantification of monomethyl succinate and dimethyl oxaloacetate, the product study allows the elucidation of an oxidation mechanism for dimethyl succinate. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 431–439, 2001     

Gleichgewichtsdruckmessungen im System Se/O/Br

Equilibrium Pressure Measurements in the System Se/O/Br The saturation pressure or saturation decomposition pressure of SeOBr_2,l, Se₂Br_2,l and SeBr_4,s were determined in a membran zero manometer. The decomposition behaviour follows from pressure measurements outside of saturation. From the equilibrium data are derived the Enthalpies of formation: Data see Inhaltsübersicht. Informations about the melting diagrams obtained via the barograms of the condensed compositions SeO₂/SeBr₄ and Se/Br.     

Neue Oxonium-Bromochalkogenate(IV) — Darstellung,Struktur und Eigenschaften von [H3O][TeBr5] · 3C4H8O2 und [H3O]2[SeBr6]

New Oxonium Bromochalcogenates(IV) — Synthesis, Structure, and Properties of [H₃O][TeBr₅] · 3 C₄H₈O₂ and [H₃O]₂[SeBr₆] Dark red crystals of the composition [H₃O][TeBr₅] · 3 C₄H₈O₂ ( 1 ) were isolated from a saturated solution of TeBr₄ in 1,4-dioxane containing a small amount of water. In this compound (space group P2₁/m, a = 8.922(4) Å, b = 13.204(7) Å, c = 9.853(5) Å, β = 91.82(4)° at 150 K) a square pyramidal [TeBr₅]^? anion has been isolated for the first time. The coordination sphere of the anion is completed to a distorted octahedron by weak interaction with a dioxane molecule of the cationic system. The [H₃O]⁺ cations are connected to chains by dioxane molecules. At room temperature the compound is stable only in its mother liquor. Crystalline [H₃O]₂[SeBr₆] ( 2 ) (space group Fm3m, a = 10.421(1) Å at 170 K) is a bromoselenous acid of high symmetry. The [H₃O]⁺ ion is only weakly coordinated by Br atoms of the anion. The anions are isolated octahedral [SeBr₆]^2? units. The structure is isotypic to the K₂[PtCl₆] structure. Despite being a halogenochalcogen(IV) acid, 2 exhibits a remarkable thermal stability. Both oxonium compounds were characterized by single-crystal X-ray structure analyses. Vibrational spectra of 2 are reported.