A Selenium‐Nitrogen Chain with Selenium in Different Oxidation States

The reaction of tBuNH₂ with a mixture of SeCl₂ and SeOCl₂ in a 6:2:1 molar ratio produces the novel selenium‐nitrogen chain ClSeN(tBu)Se(O)Cl ( 4 ), in which the selenium atoms are in two different oxidation states, Se^II and Se^IV. The crystal structure of 4 is compared with that of the related Se^II/Se^II system ClSeN(tBu)SeCl ( 1 ) and differences are attributed to hyperconjugative effects. The energetics of the formation of 4 via two different routes are elucidated by PBE0/def2‐TZVPP calculations.     

Vibrational spectroscopic investigations of snse8-n molecules

The fundamental vibrations of 13 cyclic S_nSe_8-n (n = 7—2) molecules have been calculated using a modified Urey—Bradley force field with 9–14 independent force constants whose values have been adapted from those of Se₈ and S₈. Calculated wavenumbers are compared to those obtained by Raman spectroscopy for sulfur—selenium phases prepared by recrystallizing quenched molten mixtures of the elements as previously described. Agreement between the observed spectra and calculated wavenumbers is closest by assuming the existence of selenium—selenium bonds and the absence of isolated selenium atoms in S_nSe_8-n molecules. It is assumed that sulfur—selenium phases are mixed crystals with the following components in varying concentrations: 1,2-S₆Se₂, 1,2,3-S₅Se₃, 1,2,3,4-S₄Se₄, 1,2,5,6-S₄Se₄, 1,2,3-S₃Se₅ and 1,2-S₂Se₆. The presence of S₈ and Se₈ in some of the phases is indicated by the Raman spectra.     

Reduction of elemental selenium by samarium diiodide: Selective synthesis of diorganyl selenides and diselenides

The reduction of elemental selenium by samarium diiodide led to selective formation of selenolate anion species (Se²⁻ and Se₂²⁻), the alkylation of which provided dialkyl selenides and diselenides, respectively, in excellent yields.     

Fluorocarbon-selenium chemistry: Accomplishments and quests

The binary selenium fluorides SeF_n (n = 2, 4, 6) and Se₂F₂ are considered along with corresponding perfluorohalogenoorgano- selenium compounds with selenium in the oxydation states 1, 2, 4 and 6. For lower selenium fluorides, preparation and characterisation are emphasized. Recent results in the chemistry of SeCF₂, CF₃SeCl, CF₃SeSeCF₃, CF₃Se(O)OM and CF₃Se^VI- compounds are presented. A comparison with the corresponding sulfur chemistry is also provided.     

Recent Progress in Imidoselenium Chemistry

Recent progress in imidoselenium chemistry is reviewed. Selenium diimides are thermally unstable and decompose forming a number of cyclic selenium imide derivatives Se₃(NR)₂, Se₃(NR)₃, Se₆(NR)₂, Se₉(NR)₆, OSe(μ-NR)₂SeO, RNSe(μ-NR)₂SeO, and RNSe(μ-NR)₂SO₂ (R = ^t Bu or adamantyl). All species have been structurally characterized. The experimental and theoretical evidence for the possibility of [2 + 2] cyclodimerization of selenium diimides is discussed.     

Rheniumselenidtelluride Re2SexTe5–x: Die Struktur von Re6Se8Te7

Rhenium Selenidetellurides Re₂Se_xTe_5–x: The Structure of Re₆Se₈Te₇ Well-crystallized rhenium selenidetellurides of the Re₂Te₅-type structure were prepared from the elements in evacuated sealed quartz glas tubes at 1 130 K within 14 d. The orthorhombic lattice parameters of the phases shrink with increasing selenium content from a = 1 304.9(1) ? 1 255.8(2) pm, b = 1 297.5(1) ? 1 260.0(2) pm, and c = 1 425.1(1) ? 1 408.2(1) pm. The phase width ends at composition Re₂Se_2.7Te_2.3. An X-ray structure analysis of a crystal of composition Re₆Se₈Te₇ was performed. Selenium and tellurium atoms differ structurally completely: Whereas the selenium atoms are separated within distorted octahedral [Re₆Se₈] clusters, the tellurium atoms form homonuclear bonded bicyclic [Te(Te₃)₂] units. They also link the clusters which are arranged according to the motif of a cubic closest packing.     

Na6[B18Se17]: The First Selenoborato‐closo‐dodecaborate with a Polymeric Chain Anion

Systematic studies on selenoborates containing a B₁₂ cluster entity and alkali metal cations led to the new crystalline phase Na₆[B₁₈Se₁₇] which consists of a icosahedral B₁₂ cluster completely saturated with trigonal‐planar BSe₃ units and sodium counter‐ions. Neighbouring cluster entities are connected in one direction via exocyclic selenium atoms forming the infinite chain anion ([B₁₈Se₁₆Se_2/2]^6–)_∞. The new chalcogenoborate was prepared in a solid state reaction from sodium selenide, amorphous boron and selenium in evacuated carbon coated silica tubes at a temperature of 850 °C. Na₆[B₁₈Se₁₇] crystallizes in the monoclinic space group C2/c (no. 15) with a = 18.005(4) Å, b = 16.549(3) Å, c = 11.245(2) Å, β = 91.35(3)° and Z = 4.     

Electronic structure of selenium- and tellurium-clusters

The vacuum-UV-photoelectron spectra (hν=10.0 eV or 8.3 eV) of selenium- and tellurium-clusters of different sizes (up to Se₂₅ and Te₈) were measured in a molecular beam by a photoion-photoelectron-coincidence experiment. Especially, the photoelectron spectra (4p-π-electrons) of the selenium-clusters converge with growing cluster size to the well known spectra of amorphous solid selenium by taking into account the dielectric constant of the bulk material. The experimental results indicate the first evidence that larger selenium aggregates are van der Waals clusters of the molecules Se₅, Se₆, Se₇ and Se₈ which are contained in the equilibrium vapour.     

PdCl2Se6 und PdBr2Se6, neue chalkogenreiche Komplexe von Palladium(II)-Halogeniden mit Se6-Gruppen als Liganden

PdCl₂Se₆ and PdBr₂Se₆, New Chalcogenrich Complexes of Palladium(II) Halides with Se₆ Groups as Ligands PdCl₂Se₆ und PdBr₂Se₆, chalcogenrich complexes of palladium halides with Se₆ groups as ligands have been prepared by reactions of Pd metal with melts of selenium and SeX₄ (X = Cl, Br) at 180°C in closed silica ampoules. The new compounds have been characterized by vibrational spectra and thermal analysis. The X-ray analysis of PdCl₂Se₆ showed a polymeric structure, built up by chains of linear PdX₂ groups connected by Se₆ groups in a chair conformation.     

Reactions of chloromethyloxirane and dihalopropanols with chalcogens in basic reducing systems

Chloromethyloxirane and 2,3-dibromopropan-1-ol reacted with a solution of selenium or tellurium in the system hydrazin hydrate-potassium hydroxide (K₂Se₂, K₂Te₂) to give allyl alcohol; the reaction was accompanied by regeneration of the initial free chalcogen. 1,3-Dichloropropan-2-ol reacted with selenium in the same system to give oligomeric product having a 2-hydroxypropane-1,3-diyldiseleno monomeric unit, while the reaction with tellurium led to the formation of allyl alcohol and almost complete regeneration of initial tellurium. Probable reaction mechanisms are discussed. Polyselenide oligomers containing a hydroxy group in a monomeric unit were formed in reactions of chloromethyloxirane and 1,3-dichloropropan-2-ol with selenium in the system hydrazine hydrate-2-aminoethanol. Under analogous conditions 2,3-dibromopropan-1-ol was converted into allyl alcohol with regeneration of elemental selenium. Reductive cleavage of polyselenide oligomers gave Se-methyl derivatives of 2-hydroxypropane-1,3-diselenol.     

Action of selenium on trialkylborines

Summary Trialkylborines react with selenium at 220–250° with formation of cyclic boron-selenium compounds of composition R₂B₂Se₃, olefins, and hydrogen.     

K3FeSe3 und K3Fe2Se4, zwei neue Verbindungen im System K/Fe/Se

K₃FeSe₃ and K₃Fe₂Se₄, Two New Compounds in the System K/Fe/Se The two selenides K₃FeSe₃ and K₃Fe₂Se₄ were synthesised by fusion reactions of potassium carbonate with iron and selenium in a stream of hydrogen charged with selenium at 695 °C and 710–730 °C, respectively. The crystal structures were determined by single‐crystal X‐ray diffractometer data. The atomic arrangement of K₃FeSe₃ is characterised by edge sharing [Fe₂Se₆] double tetrahedra separated by potassium ions (space group P2₁/c, Z = 4). The characteristic structural unit of the mixed‐valent compound K₃Fe₂Se₄ is a zig‐zag chain of edge‐sharing, iron‐centred selenium tetrahedra, again separated by potassium ions (space group Pnma, Z = 4).     

Organoselenido Complexes of Tungsten

Organometallic tungsten selenido complexes of the type [cpW(CO)₃]₂Se_m; m = 2 (1), 3 (2), 4 (3), can be easily synthesized via insertion of selenium into the alkali-metal tungsten bond of LiWcp(CO)₃ in appropriate ratios and subsequent oxidation of the produced W-selenolates with O₂/SiO₂. In contrast, reactions of K₂Se₆ with [cpW(CO)₃Cl] and 18-crown-6 in DMF lead to a mixture óf [cpW(CO)₃]₂Se₄ (3), the η¹ Se-bonded selenocarbamato complex [cpW(CO)₃SeC(O)NMe₂] (4) and the ionic complex [(18-crown-6)K]⁺[cpW(Se₄)₂]^? (5). The crystal structures of 3 and 4 together with their ⁷⁷Se NMR data are presented.     

Halogenation of Dibenzoselenophene and Dibenzo[1,2]diselenine

The syntheses of the selenium containing heterocycles dibenzoselenophene ( 1 ≡ biphenSe) and dibenzo[1,2]diselenine ( 2 ≡ biphenSe₂) were optimized. The halogenation reactions of 1 and 2 with XeF₂, SO₂Cl₂, Br₂ and I₂ were performed and the corresponding products characterized. In the case of 1 , the selenium(IV) dihalogenides, biphenSeF₂ ( 3 ), biphenSeCl₂ ( 4 ), biphenSeBr₂ ( 5 ), and the adduct biphenSe·I₂ ( 6 ), were isolated and identified. The extremely sensitive selenium(IV) difluoride 3 slowly formed significant amounts of an adduct with HF of the corresponding selenium(IV) oxide biphenSeO·HF ( 3a ) upon storage in glass vessels at low temperatures. In the case of 2 , the selenium(IV) trihalogenides, biphen(SeHal₃)₂ (Hal = F, Cl, Br), were found to be extremely labile (Hal = F) or not detectable (Hal = Cl, Br). Instead, as decomposition products, the selenium chloride species Se₂Cl₂, SeCl₄ and 1 were detected. In the case of Hal = I, the stable adduct biphenSe₂·I₂ ( 7 ) was isolated. In addition to characterization by multinuclear NMR spectroscopy, several molecular structures of biphen‐selenium substituted halogenides were determined.     

Bicyclische Iodtetrachalcogenatriphosphaheptane

Bicyclic Iodo-tetrachalcogena-triphospha-heptanes The compounds P₃Se_4–nS_nI (n = 0, 1, 2) have been identified by ³¹P nmr spectroscopy. They were prepared by a direct thermal reaction of red phosphorus, sulfur, selenium and iodine in the stoichiometric ratio. These iodides could be converted into corresponding bromides and chlorides by substitution reactions. All molecules show a diselenium bridge in which, in contrast to the other selenium positions, selenium could not be replaced by sulfur. Similar effects were observed for the diselenium bridges of P₂Se₅. Systematic changes of the chemical shifts and coupling constants are caused by alterations in the molecular geometry, either by replacement of selenium by sulfur, or of iodine by more electronegative ligands. An intramolecular exchange reaction is observed for all molecules.     

Synthese und Kristallstruktur von Cs3Y7Se12

Synthesis and Crystal Structure of Cs₃Y₇Se₁₂ The oxidation of yttrium metal with selenium in the presence of CsCl (7 d, 700°C, evacuated silicia tubes) results in the formation of pale yellow, lath-shaped single crystals of Cs₃Y₇Se₁₂. The crystal structure (orthorhombic, Pnnm, Z = 2, a = 1272.8(3), b = 2627.7(5), c = 413.32(8) pm) consists of edge- and vertex-connected [YSe₆] octahedra forming a rocksalt-related network [Y₇Se₁₂]^3?. One-dimensional infinite channels along [001], apt to take up extra cations, provide coordination numbers of 6 and 7 + 1, respectively, for two crystallographically different Cs⁺.     

Selen‐Polykationen stabilisiert durch polymere Chlorobismutat‐Anionen: Synthesen und Kristallstrukturen von Se4[Bi4Cl14] und Se10[Bi5Cl17]

Selenium Polycations Stabilized by Polymeric Chlorobismuthate Anions: Syntheses and Crystal Structures of Se₄[Bi₄Cl₁₄] and Se₁₀[Bi₅Cl₁₇] Reactions of selenium with selenium(IV) chloride and bismuth(III) chloride in sealed evacuated glass ampoules at temperatures between 110 and 155 °C yield a series of compounds which are composed of discrete selenium polycations and polymeric chlorobismutate anions. Besides the already known Se₈[Bi₄Cl₁₄] two new compounds have been identified by crystal structure analyses as Se₄[Bi₄Cl₁₄] (tetragonal, P4/n, a = 1089.1(2) pm, c = 993.7(2) pm, Z = 2) and Se₁₀[Bi₅Cl₁₇] (monoclinic, P2₁/c, a = 1079.24(8) pm, b = 2062.9(2) pm, c = 1676.1(2) pm, β = 90.87(1)°, Z = 4). Se₄[Bi₄Cl₁₄] was obtained as red transparent platelike crystals and is the first example of a compound with (chalcogen₄)²⁺ ions of exact square‐planar symmetry and molecular point group D_4h in the solid state. The cations are surrounded by layers of two‐dimensional polymeric anions [Bi₄Cl₁₄]^2–. Se₁₀[Bi₅Cl₁₇] forms dark grey crystals with a reddish luster. The structure contains the known bicyclic polycation Se₁₀²⁺ which is disordered over two positions and the first three‐dimensional polymeric chlorobismutate anion [Bi₅Cl₁₇]^2–. The different BiCl_x polyhedra are linked by sharing common vertices, edges, and faces.     

Anaerobic and aerobic sorption of cesium and selenium on mudrock

This study is focused on sorption and determination of distribution ratios (R _d) of cesium and selenium on mudrock, which is the potential host rock for waste disposal in Taiwan. Batch tests including sorption kinetic and isotherms tests have been performed in synthetic groundwater at aerobic and anaerobic conditions which might be found in the deep geologic environment. It is found that R _d for sorption of cesium did not have an obvious difference in both conditions with various contact time. However, R _d in anaerobic condition for sorption of selenium was greater than that in aerobic condition. Selenium is a redox sensitive element and its solubility in reducing conditions is controlled by the formation of metallic or precipitable selenium. It demonstrated variation of R _d with time in both conditions for Se sorption kinetic experiments was equal (10 ml/g) and indicated a part formation (10%) of precipitable selenium (Se⁰, FeSe or FeSe₂) in the solution. Moreover, it was not enough to form precipitable selenium completely in reducing condition as to insufficient experimental period (2 weeks) and in the presence of Fe²⁺. The Freundlich and Langmuir isotherm for the concentration ranges (i.e., 10⁻³–10⁻⁷M) conducted in both conditions seem to be adequate to quantitatively describe the sorption of cesium and selenium, respectively.     

Stabilization of charged and neutral defects and formation of centers with negative correlation energy in a-Se

Quantum-chemical modeling of the stabilization of neutral and charged defects in amorphous selenium (a-Se) has been carried out taking into account their interaction with distant fragments of a continuous random network (CRN) within the polarizable continuum model (PCM). For the neutral defects (Se ₃ ⁺ -Se ₁ ^? and Se ₄ ⁰ ) stabilization is due to additional chemical bonds with the nearest environment of the defect, whereas, for charged defects, the interaction with the CRN, with an energy as large as 3 eV, is also significant. The energy of formation of charged defects E _def becomes close to the energy E _b = 2 eV of homolytic bond cleavage. Interaction of defects can be responsible for extra stabilization. The neutral defect Se ₃ ⁺ -Se ₁ ^? forms a complex with the charged defect Se ₃ ⁺ with a decrease in energy by 0.51 eV. Such a complex can exemplify centers with negative correlation energy, which are used for explaining some experimentally observed specific features of chalcogenide glassy semiconductors.     

Ultraviolet photoelectron studies of the molecules Se5, Se6, Se7 and Se8 with relevance to their geometrical structure

The vacuum-UV-photoelectron spectra (hν=10.0 eV) of Se₂, Se₅, Se₆, Se₇ and Se₈ were measured. The isolated particles were examined in a supersonic molecular beam employing the photoelectron-photocation-coincidence technique. The structures of the photoelectron spectra of selenium molecules with even and odd numbers of atoms differ in a characteristic manner. Whereas the spectra of Se₆ and Se₈ show one single broad band, three separated bands with different intensities are observed for Se₅ and two for Se₇. An attempt to connect these experimental observations with the geometrical structure of the molecules shows that the photoelectron spectra are consistent with theC _1h -symmetry of the Se₅ and Se₇ rings proposed in the literature.