Weak Se Research Articles

Water Encapsulated [(Fe4Se4)Se4]6- Clusters in [Na6(H2O)18][Fe4Se8

[Na6(H2O)18][Fe4Se8] was synthesized using hydrothermal methods and characterized by single-crystal X-ray diffraction, 57Fe Mössbauer spectroscopy, magnetization, and muon spin resonance (μSR) measurements. The cubic crystal structure (space group I23, a = 11.785 Å, Z = 2) contains heterocubane-type clusters with Td symmetry. Four additional selenium atoms complete the tetrahedral coordination around the iron atoms, forming units. Notably, the selenide ligands do not interact with the sodium cations, as the Fe4Se86- cluster in [Na6(H2O)18][Fe4Se8] is exclusively surrounded by water molecules via weak Se···H-O hydrogen bonds. This is particularly remarkable given that [Fe4Q4] clusters are typically unstable in water. Quantum chemical calculations (DFT) confirm the crystal structure and improve the positions of the hydrogen atoms. 57Fe Mössbauer spectroscopy reveals that the spin ordering of the mixed-valence [Fe42.5+Se4]2+ cluster core mirrors the antiparallel spin arrangement found in analogous iron-sulfur clusters, such as , in protein-bound systems. An increase of the quadrupole splitting at low temperatures indicates changes of the orbital occupations. μSR Experiments show a reduction of the spin fluctuation frequency until the system becomes static at low temperatures, but no evidence of a S = 0 state above 2 K.

Accumulation and Pollution Risks of Heavy Metals in Soils and Agricultural Products from a Typical Black Shale Region with High Geological Background

Soil polluted by heavy metals (HMs) is an important environmental issue in China, and regional geological background is a vital factor that influences the enrichment of HMs in soils. Previous studies have shown that soils derived from black shales are commonly enriched in HMs and present high potential eco-environmental risks. However, few studies have investigated the HMs in different agricultural products, which inhibit the safe use of land and safe production of food crops in black shale regions. This study investigated the concentrations, pollution risks, and speciation of HMs in soils and agricultural products from a typical black shale region in Chongqing. The results showed that the study soils were enriched in Cd, Cr, Cu, Zn, and Se but not in Pb. Approximately 98.7% of total soils exceeded the risk screening values, and 47.3% of total soils exceeded the risk intervention values. Cd had the highest pollution level and potential ecological risks and was the primary pollutant in soils of the study area. Most of the Cd resided in ion-exchangeable fractions (40.6%), followed by residual fractions (19.1%) and weak organic matter combined fractions (16.6%), whereas Cr, Cu, Pb, Se, and Zn were dominated by residual fractions. Additionally, organic combined fractions contributed to Se and Cu, and Fe-Mn oxide combined fractions contributed to Pb. These results indicated that Cd had higher mobility and availability than those of other metals. The agricultural products presented a weak ability to accumulate HMs. Approximately 18.7% of the collected samples with Cd exceeded the safety limit, but the enrichment factor was relatively low, indicating low pollution risks of the heavy metals. The findings of this study could provide guidelines for safe use of land and safe production of food crops in black shale regions with high geological background.

Plume bulge observed in the Pearl River Estuary in summer: Spatiotemporal characteristics and influencing factors

Plume bulges were once thought to be less prone to form in an estuary with trumpet-like characteristics, such as the Pearl River Estuary (PRE), where no plume bulge has previously been detected by hydrological observations. However, based on large scale simultaneous observations, the formation dynamic of a plume bulge in the PRE during the flood-ebb tidal cycle is characterized in this paper. The influences of discharge change on the plume bulge are revealed through the different motion processes of the surface-advected plume and tidal plume. The results show that during spring tide with a weak SE wind and high river discharge (20,725 m3 s−1), a plume bulge in the PRE is produced on the south side of the Dawanshan Islands outside the estuary. Based on the standardization stratification coefficient calculation method and the salinity decomposition method, it was found that the tidal plume is the main component forming the plume bulge rather than the surface-advected plume. The 25 isohaline indicated the boundary of the PRE plume bulge. However, when the discharge was reduced by approximately 43%, no plume bulge was observed. River discharge had a considerable impact on the formation of plume bulges as higher discharge was favorable in enhancing the momentum and flux of the tidal plume in the longitudinal Lantau Channel, whereas lower discharge was favorable for the formation of a surface-advected plume flowing along the west bank.

Activation of alkynes by chalcogen bonding: a Se⋯π interaction catalyzed intramolecular cyclization of 1,6-diynes.

The activation of the triple bond of alkynes was dominated by transition metals, while it is difficult for organocatalysts to play an effective role in this realm. Herein, we describe the activation of alkynes by chalcogen bonding, and the weak Se⋯π interaction was capable of catalyzing the intramolecular cyclization of 1,6-diynes, thus adding a new capability in the list of supramolecular catalysis.

Increasing unsaturated Se number and facilitating atomic hydrogen adsorption of WSe2+x nanodots for improving photocatalytic H2 production of TiO2

A versatile tactic of unsaturated selenium-enrichment regulation is developed, which can not only increase the active Se number, but also reinforce the weak Se–Hads bonds via constructing electron-poor Se(2−δ)− active sites.

Annual Dynamics of Phytoplankton in the Black Sea in Relation to Wind Exposure

Studies of the annual dynamics of phytoplankton in the NE Black Sea at two stations on the shelf and the continental slope were conducted in 2016, 2017, and 2019. The species composition of phytoplankton has not undergone significant changes compared to previous decades. The coccolithophore Emiliania huxleyi, small flagellates, and diatoms determined the abundance of phytoplankton; and diatoms, coccolithophores, and dinoflagellates determined the total biomass. The annual dynamics of the satellite-derived chlorophyll-a showed peaks in spring and autumn, and sometimes in summer. During the stratified water column period, strong winds in most cases led to a detectible increase in chlorophyll-a. The annual dynamics of phytoplankton followed the pattern: small diatoms (spring) → coccolithophores (late spring, early summer) → large diatoms (summer, autumn). Such a pattern was typical for the previous decades. Coccolithophores dominated in weak SE winds, diatoms in NE winds. The combined effect of sustained offshore wind and strong current can cause diatom blooms during stratified water, even if the wind velocity is moderate.

Promoting the energy storage capability via selenium-enriched nickel bismuth selenide/graphite composites as the positive and negative electrodes

Hybrid metal chalcogenides incorporating prolific redox-active transition metal selenides with optimized interactions are suitable candidates to boost the electrochemical properties of supercapacitors. The present study elaborates the design and application of selenium (Se)-enriched reduced graphene oxide hybridized heterostructured nickel bismuth selenide (RGO/Ni-Bi-Se) and bismuth selenide (RGO/Bi2Se3)-based electrode materials by a simple in-situ growth solvothermal reaction for advanced battery-type supercapacitors. Integrating the advantages of different components, good electrical conductivity of RGO and Se-enrichment induce a strong collaborative effect on redox reactions. The favourable structural and compositional features are not only desirable for the capacitive and rate performance enhancement but also for volume change mitigation during successive charge–discharge processes. The heterostructured RGO/Ni-Bi-Se delivers a boosted electrochemical behavior with an exceptional specific capacity (220.2 mAh g–1 at 1 A g–1) and good rate performance (54.8% capacity retention at 50 A g–1). The strong synergy between the Ni and Bi active components with multielectron reversible Faradic redox reactions optimizes the overall electrochemical performances and modifies the charge storage capability of the electrode material. The interconnected porous nanoarchitectures are regulated with abundant interface engineering and disorders, thereby achieving a large electrode/electrolyte area at junction and shortening the ion diffusion paths as well as accelerating the electron-transmission ability during operation. On the other hand, the as-obtained RGO/Bi2Se3 negative electrode material exhibits better pseudocapacitive properties with favourable reversibility and displays a large specific capacitance of 464 F g–1 at 1 A g–1. The RGO fabric not only offers a solid skeleton for the self-assembly of building units but also enlarges the specific area for more electrochemical active sites and decreases the charge transfer resistance. The formation of weak electronegative Se is profitable to adjust the electronic configuration of exposed Ni/Bi sites. More significantly, the heterostructured RGO/Ni-Bi-Se reveals a well-matched performance with the capacitive RGO/Bi2Se3 and the established aqueous battery supercapacitor hybrid (BSH) device achieves admirable energy density of 62.3 Wh kg−1 at a power density of 949.7 W kg−1 together with 89.2% retention after 10 000 cycles.

MOF derived ZnO/C@(Ni,Co)Se2 core–shell nanostructure on carbon cloth for high-performance supercapacitors

To achieve a high energy density of nickel cobalt bimetallic selenide electrode materials, the key points are on the construction of porous materials and control of the appropriate proportion of active materials. Here, a well-design structure MOF derived ZnO/C@(Ni,Co)Se2 core–shell nanostructure on carbon cloth was prepared for the first time. The ZnO/C@(Ni,Co)Se2 core–shell nanostructure electrode exhibits the ascendant specific capacity of 164.18 mA h g−1 at 1 A g−1. The as-obtained ZnO/C@(Ni,Co)Se2//AC asymmetric supercapacitor shows the superior energy density of 65.67 W h kg−1 at 800 W kg−1, with 97.87% capacitance retention after 10,000 cycles. The stable self-supporting MOF derived porous carbon material as the core not only provides a strong support structure for thin shell nanosheets but also enhances the specific surface area. An appropriate proportion of Ni/Co and the existence of weak electronegative Se is profitable to improve the electronic structure of the (Ni,Co)Se2 thin nanosheet shell. Besides, the synergistic effect between the active materials can also optimize the electrochemical performance of the electrode materials. Thus, our work offers a new strategy for MOF derived porous carbon to construct flexible electrode materials with high electrochemical performance.

Trace element chemistry of atmospheric deposition along the Wasatch Front (Utah, USA) reflects regional playa dust and local urban aerosols

Atmospheric deposition to urban areas and mountain snowpack often contains a mixture of playa dust and anthropogenic aerosols, yet the relative contribution of trace elements from each source is not well understood. To evaluate dust contributions from regional playas to an urban area, we sampled playa dust sources, urban dust deposition, and snow dust deposition across the Wasatch Front in northern Utah, USA. Dust samples were analyzed for trace and major element chemistry, grain size distribution, and mineralogy. Playa, urban, and snow dust samples contained similar mineralogy, dominated by silicate, carbonate, and evaporite minerals. Grain size distribution between playa, urban, and snow dust samples was also similar, suggesting that playas are a primary dust source for the region. Principal component analysis and enrichment diagrams revealed similar chemistry of playa, urban, and snow dust with some exceptions. Compared with playa dust, urban and snow dust had lower concentrations of Li, Na, Sr, U, Mg, and Ca and higher concentrations of Fe, Al, Be, Sb, Se, Mo, Cr, La, and Cu. The first set of elements are found in evaporite- and carbonate-minerals while the second set of elements are sourced from anthropogenic activities. Mass balance calculations suggest that 90% of the dust mass deposited to the Wasatch Front is from playas, with small additions from local sources that alter the dust chemistry. Sequential leaching of dust samples showed that some elements were readily leached with weak acids, including B, K, Na, Sr, Ca, U, Mo, Cd, and Se, suggesting that they are environmentally available and may serve as important macronutrients or contaminants to ecosystems. This is the first study to directly compare the geochemistry of playa dust sources with dust deposition to urban areas and mountain snowpack in the western US, with implications for understanding how water diversions, land use changes, and population growth may affect the regional dust cycle in the future.

Retention of selenium by calcium aluminate hydrate (AFm) phases under strongly-reducing radioactive waste repository conditions.

Safety assessment studies of future nuclear waste repositories carried out in many countries predict selenium-79 to be a critical radionuclide due to its presence as anion in three relevant oxidation states (vi, iv, -ii) resulting in weak retardation by most common rock minerals. This assumption, however, ignores its potential uptake by AFm phases, positively charged anion exchangers, which are present in significant quantities in the cementitious materials used in artificial barriers. Here we report for the first time wet chemistry and spectroscopic data on the interaction of the most relevant selenium anion species under the expected strongly reducing conditions, i.e. HSe-, with two AFm phases commonly found in cement, monocarbonate (AFm-MC) and hemicarbonate (AFm-HC). Batch sorption experiments showed that HSe- is retained much more strongly by AFm-HC (solid-liquid distribution ratio, Rd, of 100 ± 50 L kg-1) than by AFm-MC (Rd = 4 ± 2 L kg-1) at the equilibrium pH (∼12). X-ray absorption fine-structure (XAFS) spectroscopy revealed that the larger d-spacing in AFm-HC (d-spacing = 8.2 Å) provides easy access for HSe- to the AFm interlayer space for sorption, whereas the smaller d-spacing of AFm-MC (d-spacing = 7.55 Å) hinders interlayer access and limits HSe- sorption mostly to the outer planar surfaces and edges of the latter AFm phase. XAFS spectra further demonstrated that Se(-ii) prevalently sorbed in the interlayers of AFm-HC, is better protected from oxidation than Se(-ii) prevalently sorbed onto the outer surfaces of AFm-MC. The quantitative sorption data along with the molecular-scale process understanding obtained from this study provide crucial insight into the Se retention by the cementitious near-field of a radioactive waste repository under reducing conditions.

Halogen-Bonding Interactions of Polybrominated Diphenyl Ethers and Thyroid Hormone Derivatives: A Potential Mechanism for the Inhibition of Iodothyronine Deiodinase.

Polybrominated diphenyl ethers (PBDEs) increase flame resistance in consumer goods, but these compounds and their hydroxylated derivatives (OH-BDEs) impair normal thyroid function. Halogen bonding (XB) of PBDEs to an active site selenocysteine may prevent iodothyronine deiodinase(Dio)-catalyzed activation/deactivation of thyroid hormone (TH) derivatives. In this study, we compare the strength of the XB interactions of TH derivatives, iodine-based contrast agents and PBDEs/OH-BDEs with a methylselenolate model of the Dio active site using density functional theory calculations. The strength of the XB interaction depends upon the acceptor halide, the position of the halide, the number of ring substituents, and the proximity of hydroxyl groups to the XB site. The weaker Se⋅⋅⋅Br interactions relative to Se⋅⋅⋅I interactions are consistent with a model of competitive inhibition that blocks binding of THs at elevated PBDE/OH-BDE concentrations. XB interactions were generally more favorable at ortho and meta positions and in substrates with more electron-withdrawing substituents. PBDEs/OH-BDEs that mimic the binding behavior of THs, that is, containing ortho and meta bromides and adjacent hydroxyl groups, may be the most effective inhibitors. Highly-brominated PBDEs/OH-BDEs have comparable interaction energies to THs and may undergo debromination. These results may also suggest that XB strength must exceed a threshold value in order for PBDEs/OH-BDEs to undergo nucleophilic attack by Dio.

Effect of a Bromo Substituent on the Glutathione Peroxidase Activity of a Pyridoxine-like Diselenide.

In search for better mimics of the glutathione peroxidase enzymes, pyridoxine-like diselenides 6 and 11, carrying a 6-bromo substituent, were prepared. Reaction of 2,6-dibromo-3-pyridinol 5 with sodium diselenide provided 6 via aromatic nucleophilic substitution of the 2-bromo substituent. LiAlH4 caused reduction of all four ester groups and returned 11 after acidic workup. The X-ray structure of 6 showed that the dipyridyl diselenide moiety was kept in an almost planar, transoid conformation. According to NBO-analysis, this was due to weak intramolecular Se···O (1.1 kcal/mol) and Se···N-interactions (2.5 kcal/mol). That the 6-bromo substituent increased the positive charge on selenium was confirmed by NPA-analysis and seen in calculated and observed (77)Se NMR-shifts. Diselenide 6 showed a more than 3-fold higher reactivity than the corresponding des-bromo compound 3a and ebselen when evaluated in the coupled reductase assay. Experiments followed for longer time (2 h) confirmed that diselenide 6 is a better GPx-catalyst than 11. On the basis of (77)Se-NMR experiments, a catalytic mechanism for diselenide 6 was proposed involving selenol, selenosulfide and seleninic acid intermediates. At low concentration (10 μM) where it showed only minimal toxicity, it could scavenge ROS produced by MNC- and PMNC-cells more efficiently than Trolox.

A Synthetic and Structural Study of Arylselenoamides and 2,4-Diaryl-1,3- Selenazoles

The systematic preparation of 2,4-diaryl-1,3-selenazoles was carried out by two-component cyclization of the primary selenoamides with α-halo ketones. Selenoamides were obtained from the reaction of Woollins’ reagent with arylnitrile, followed by hydrolysis with water. Three selenoamides have close structural similarities along with intermolecular interactions such as the strong N–H···O hydrogen bonding, the weak N–H···Se, C–H···O/N/Se intermolecular interactions and π–π stacking interactions; meanwhile, the newly formed five-membered N–C–Se–C–C rings in ten 2,4-diaryl-1,3-selenazoles have either planar or near-planar conformations along with the weak C–H···O/N/Se/Br/Cl intermolecular interactions and π–π stacking interactions. In addition, the weak Se···Se close contacts in four cases and the C–H···N intramolecular interactions in two structures were also observed within the all solid structures.

Intra- and intermolecular Se···X (X = Se, O) interactions in selenium-containing heterocycles: 3-benzoylimino-5-(morpholin-4-yl)-1,2,4-diselenazole.

In the selenium-containing heterocyclic title compound {systematic name: N-[5-(morpholin-4-yl)-3H-1,2,4-diselenazol-3-ylidene]benzamide}, C13H13N3O2Se2, the five-membered 1,2,4-diselenazole ring and the amide group form a planar unit, but the phenyl ring plane is twisted by 22.12 (19)° relative to this plane. The five consecutive N-C bond lengths are all of similar lengths [1.316 (6)-1.358 (6) Å], indicating substantial delocalization along these bonds. The Se···O distance of 2.302 (3) Å, combined with a longer than usual amide C=O bond of 2.252 (5) Å, suggest a significant interaction between the amide O atom and its adjacent Se atom. An analysis of related structures containing an Se-Se···X unit (X = Se, S, O) shows a strong correlation between the Se-Se bond length and the strength of the Se···X interaction. When X = O, the strength of the Se···O interaction also correlates with the carbonyl C=O bond length. Weak intermolecular Se···Se, Se···O, C-H···O, C-H···π and π-π interactions each serve to link the molecules into ribbons or chains, with the C-H···O motif being a double helix, while the combination of all interactions generates the overall three-dimensional supramolecular framework.

The reactions of para-halo diaryl diselenides with halogens. A structural investigation of the CT compound (p-FC6H4)2Se2I2, and the first reported “RSeI3” compound, (p-ClC6H4)SeI·I2, which contains a covalent Se–I bond

The reactions of the diaryl-diselenides (p-FC(6)H(4))(2)Se(2) and (p-ClC(6)H(4))(2)Se(2) with diiodine have been investigated. Species of stoichiometry "RSeI" are formed when the ratio employed is 1:1. The solid-state structure of "(p-FC(6)H(4))SeI" has been determined, and shown to be a charge-transfer (CT) adduct, (p-FC(6)H(4))(2)Se(2)I(2), where the Se-Se bond is retained and the diiodine molecule interacts with only one of the selenium atoms. The Se-I bond in (p-FC(6)H(4))(2)Se(2)I(2) is 2.9835(12) Å, which is typical for a (10-I-2) Se-I-I CT system. When diiodine is reacted in a 3:1 ratio with (p-XC(6)H(4))(2)Se(2) (X = F, Cl) species of stoichiometry "RSeI(3)" are formed. The structure of "(p-ClC(6)H(4))SeI(3)" reveals that this is not a selenium(IV) compound, but is better represented as a selenium(II) CT adduct, (p-ClC(6)H(4))SeI·I(2). The Se-I bond to the diiodine molecule is typical in magnitude for a CT adduct, Se-I: 2.8672(5) Å, whereas the other Se-I bond is much shorter, Se-I: 2.5590(6) Å, and is a genuine example of a rarely observed covalent Se-I bond, which appears to be stabilised by a weak Se···I interaction from a neighbouring iodine atom. The reaction of (p-ClC(6)H(4))SeI with Ph(3)P results in the formation of a CT adduct, Ph(3)PSe(p-ClC(6)H(4))I, which has a T-shaped geometry at selenium (10-Se-3). By contrast, the reaction of (p-FC(6)H(4))SeI with Ph(3)P does not form an adduct, but results in the formation of Ph(3)PI(2) and (p-FC(6)H(4))(2)Se(2).

The Reactions of Thianthrene and Selenanthrene with AlCl3: Coordination Complexes, Radical Ions, and Investigations on the Unique Triple‐Decker Molecule (Thianthrene)32+

AbstractThe reactions of thianthrene (TA) and selenanthrene (SeA) with AlCl3 were studied in the melt phase and with liquid SO2 as solvent. From neat AlCl3 and TA, the colorless complex [AlCl3(TA)] was isolated as the main product and the dark red salt (TA)3[Al2Cl7]2 as the byproduct. The analogous solvent‐free reaction of selenanthrene and AlCl3 takes a different course as colorless [Al(SeA)3][Al2Cl7]3 is formed in quantitative yield. With SO2 as solvent, both TA and SeA give the black radical salts (TA)2[AlCl4]2 and (SeA)2[AlCl4]2, respectively. In the structure of [AlCl3(TA)], thianthrene acts as a monodentate ligand and coordinates with one S atom to the pyramidal AlCl3 unit. The structure of the (TA)32+ ion is a stack of three almost planar TA molecules in parallel arrangement. [Al(SeA)3]3+ represents a tris‐chelate complex ion with SeA acting as a bidentate ligand and both Se atoms binding to the octahedrally coordinated Al3+ ion. (SeA)2[AlCl4]2 consists of dimers of SeA+ radical ions, which are bound by weak intermolecular Se···Se bonds. Tentative reaction equations are given to explain the unexpected oxidation processes that lead to the radical ions. Quantum chemical calculations were performed on the molecular fragments and on the periodical structures. The trimeric (TA)32+ ion is in the singlet state in accordance with the magnetic properties of (TA)3[Al2Cl7]2, which show a weak temperature‐independent paramagnetism. The ion is bound by long‐range four‐center bonds between the outer two radicals.

Structural isomerism in (p-XC6H4)SeCl3 and (p-XC6H4)SeBr3 (X = F, Cl) compounds. Co-crystallisation of cis- and trans-dimeric forms of (p-ClC6H4)SeCl2(μ-Cl)2(p-ClC6H4)SeCl2. A new structural modification for the “PhSeBr” reagent, Ph2Se2Br2, containing an elongated Se–Se bond

A series of di(para-halophenyl)diselenides, (p-XC(6)H(4))(2)Se(2) (X = F, Cl) have been reacted with three equivalents of SO(2)Cl(2) or Br(2), leading to the formation of selenium(iv) RSeX(3) compounds. The structures of (p-FC(6)H(4))SeX(3) (X = Cl, Br) have been determined, and both exhibit a dimeric RSeX(2)(μ-X)(2)RSeX(2) structure consisting of two "saw-horse" (p-FC(6)H(4))SeX(3) units linked by two halide bridges, with an overall square pyramidal geometry at selenium. In both structures all the selenium and halogen atoms are planar, with both aryl rings located on the same side of the Se(2)X(6) plane (cis-isomer). The structure of (p-ClC(6)H(4))SeCl(3) also adopts a planar dimeric structure, however both cis- and trans-dimeric molecules are co-crystallised in the unit cell. In contrast, the structure of (p-ClC(6)H(4))SeBr(3) adopts a folded cis-dimeric structure due to steric constraints. Secondary Se···X interactions to the "vacant" sixth coordination site at selenium are a feature of most of these structures, but are most prominent in the folded structure of (p-ClC(6)H(4))SeBr(3). A re-examination of the PhSeBr/PhSeBr(3) system resulted in the isolation of crystals of a second structural form of "PhSeBr". The structure of Ph(2)Se(2)Br(2) consists of two PhSeBr units linked by an elongated Se-Se bond of 2.832(4) Å, and longer secondary Se···Br interactions of 3.333(4) Å to form a chain structure. Further weak Se···Br and Br···Br interactions are present, which form loosely linked rippled sheets of selenium and bromine atoms, similar to the sheets observed for the tetrameric form, Ph(4)Se(4)Br(4).

1,3-Benzothia-zole-2(3H)-selone.

The title compound, C7H5NSSe, is the product of the reaction of 2-chloro­benzothia­zole with sodium hydro­selenide. The mol­ecule is almost planar (r.m.s. deviation = 0.018 Å) owing to the presence of the long chain of conjugated bonds (Se=C—N—C=C—C=C—C=C). The geometrical parameters correspond well to those of the analog N-methyl­benzothia­zole-2(3H)-selone, demonstrating that the S atom does not take a significant role in the electron delocalization within the mol­ecule. In the crystal, mol­ecules form centrosymmetric dimers by means of inter­molecular N—H⋯Se hydrogen bonds. The dimers have a nonplanar ladder-like structure. Furthermore, the dimers are linked into ribbons propagating in [010] by weak attractive Se⋯S [3.7593 (4) Å] inter­actions.

Bis(pyridazine-κN)bis(selenocyanato-κN)zinc

The asymmetric unit of the title compound, [Zn(NCSe)2(C4H4N2)2], consists of one ZnII cation, located on a twofold rotation axis, one seleno­cyanate anion and one pyridazine ligand in general positions. The ZnII atom is coordinated by two N-atoms of two pyridazine ligands and two terminal N-bonded seleno­cyanate anions within a slightly distorted tetra­hedral coordination environment. In the crystal, discrete complex mol­ecules are arranged in layers parallel to the ac plane, with ZnII⋯ZnII distances of 8.0906 (6) Å along the a axis and of 9.0490 (7) or 9.3604 (7) Å along the c axis. The complex mol­ecules are further linked via weak Se⋯Se inter­actions, with Se⋯Se distances of 3.8235 (9) Å.

Devitrification behavior and some electrical properties of GeSeTl chalcogenide glass

The activation energy of crystallization E c of GeSe 3Tl 0.3 and GeSe 4Tl 0.3 chalcogenide glasses was calculated from the shift of the DTA exothermic peaks with changing the heating rate. Values of E c were calculated by different methods and it was found that it decreases with increasing Se content. Amorphous thin films of the present glasses were prepared using thermal evaporation technique. Electrical conductivity and I– V characteristics have been studied at temperatures below the glass transition temperature T g and over a wide range of thickness (57.4–680 nm). The dc conductivity was linear in the Arrhenius Plot in the considered temperature range and increases with the increase of Se content. The activation energy for the dc conduction Δ E σ is decreased with increasing Se content and film thickness. The observed compositional dependence of Δ E σ has been correlated with the increase of weak Se–Se bond density at the expense of strong Ge–Se bond density. I– V characteristic curves indicates the memory type switching phenomenon for these compositions and it is explained in accordance with the electrothermal model initiated from Joule heating of a current channel.