Te Contacts Research Articles

Highly Stable Metal─Na0.02Pb0.98Te Contacts for Medium Temperature Thermoelectric Devices.

In the medium temperature (600-850 K) range, Na0.02Pb0.98Te is a highly efficient p-type thermoelectric compound. Device fabrication utilizing this compound for power generation demands highly stable low-contact resistance contacts with metal electrodes. This work investigates the microstructural, electrical, mechanical, and thermochemical stability of Na0.02Pb0.98Te-metal (Ni, Fe, and Co) contacts made by a one-step vacuum hot pressing process. Direct contact mostly resulted in either an interface with poor mechanical integrity, as in Co and Fe, or poisoning of the TE compound, as in the case of Ni, which results in high specific contact resistance (rc). In Ni and Co, adding a SnTe interlayer lowers the rc and strengthens the contact. It does not, however, effectively stop Ni from diffusing into Na0.02Pb0.98Te. The bonding is poor in the Fe/SnTe/Na0.02Pb0.98Te contacts due to the absence of any reaction at the Fe/SnTe interface. A composite buffer layer Co + 75 vol % SnTe with SnTe improves the mechanical stability of the Co contact with moderately lesser rc than pure SnTe alone. However, a similar approach with Fe does not yield stable contact. The Co/Co + 75 vol % SnTe/SnTe/Na0.02Pb0.98Te contact exhibits rc less than 50 μΩ cm2 and has good microstructural and mechanical stability after annealing at 723 K for 170 h.

Metalloid Chalcogen–pnictogen σ-hole bonding competition in stibanyl telluranes

In this manuscript a curious behavior observed in the solid state of several X-ray structures retrieved from the Cambridge structural database (CSD) is described and analyzed. These structures have in common the presence of a metalloid–metalloid pnictogen (Pn)–chalcogen (Ch) covalent bond (i.e., Sb–Te bond) in the structure. The Sb–Te bond presents different σ-holes at both ends of the bond in terms of size and intensity. These compounds have a tendency to form short intermolecular Sb•••Te interactions in the solid state. The aim of this work is to investigate, by using dispersion-corrected density functional theory (DFT-D3) calculations, whether the Sb•••Te contacts observed in the solid state correspond to PnB (Sb is the Lewis acid) or ChB (Te is the Lewis acid). Moreover, using two model stibanyl telluranes, the interaction energies with a series of Lewis bases and anions using both ends of the Sb–Te covalent bond have been computed to investigate which side (PnB or ChB donor) is able to establish stronger interactions with common electron rich atoms. Finally, several computational tools such as the quantum theory of atoms-in-molecules (QTAIM), noncovalent interaction plot (NCIPlot) index and electron localization (ELF) function (2D and 3D maps) have been used to further characterize the physical nature of the Sb•••Te interactions. The results reported herein suggest that in the Sb•••Te contacts the Te atom acts as σ-hole donor and the Sb as electron density donor.

Electronic properties of XPtY-Graphene (X/Y = S, Se and Te) contacts

Abstract Janus transition metal dichalcogenides attracts increasing attention because the out-of-plane mirror symmetry is broken. Here, using the first-principles methods based on density functional theory, the structural and electronic characteristics of monolayer Janus XPtY (X/Y = S, Se or Te, and X ≠ Y) and their van der Waals heterojunctions (vdWHs) with monolayer and bilayer graphene have been systematically investigated. Monolayer Janus SePtS, TePtS and TePtSe are semiconductor with indirect band gaps of 1.94, 1.05 and 0.72 eV, respectively. Interestingly, the different stacking configuration can induce different contact type (n-type, p-type Schottky contact and Ohmic contact). Moreover, the Schottky barrier height (SBH) and type of contact in the vdWHs can be adjusted by applying an external electric field (E-field). These findings in this paper are expected to provide useful guidance for the design of new nanodevices based on the vdWHs of Janus XPtY and graphene.

CpFe(CO)2TePh as a ligand for organometallic dihalides Fe(CO)4I2, (p-Cymene)RuI2, and Me5C5RhI2: Synthesis and molecular structures

CpFe(CO)2TePh (I) can substitute one carbonyl group in Fe(CO)4I2 providing Fe(CO)3I2(μ-TePh)Fe(CO)2Cp (II) or play role of ligand to monomeric fragments [(p-Cymene)RuI2] and [Сp*RhI2] (p-Cymene = (η6-1-isopropyl-4-methylbenzene); Сp* = η5-pentamethylcyclopentadienyl) provides the complexes (p-Cymene)RuI2(μ-TePh)Fe(CO)2Cp (III) and Cp*RhCl2(μ-TePh)Fe(CO)2Cp (IV), respectively. The single-crystal X-ray diffraction of complexes II–IV (CIF files CCDC nos. 1038124 (II), 1038127 (III), 1038125 (IV)) revealed the shortening of М–Те bonds and the presence of intramolecular I…Te contacts.

Synthesis, crystal structure, and thermal stability of ionic cluster compounds (phenH)4[Re4Q4(CN)12]·nH2O (Q = S, Se, n = 6; Q = Te, n = 10)

Three new salts of tetrahedral rhenium chalcocyanide cluster anions [Re4Q4(CN)12]4− (Q = S, Se, Te) and 1,10-phenanthroline-1-ium cations, (phenH)4[Re4S4(CN)12]·6H2O (1), (phenH)4[Re4Se4(CN)12]·6H2O (2), and (phenH)4[Re4Te4(CN)12]·10H2O (3), have been synthesized by reactions of K4[Re4Q4(CN)12]·nH2O with 1,10-phenanthroline in the presence of Nd3+ in an acidic aqueous medium (pH 4). 1 and 2 exhibit similar 2-D layered supramolecular architectures based on hydrogen bonds between water molecules, CN-groups of cluster anions, and phenH+ cations. The latter are involved in π–π and C–H⋯π stacking interactions, connecting the adjacent layers with each other. Complex 3 demonstrates a 3-D framework based on hydrogen bonds between water molecules and CN-groups, π–π and C–H⋯π interactions. Notably short O···Te contacts of 3.40 and 3.50 Å are found in the structure of 3. The thermal properties of 1–3 have been investigated by TG-DTG.

Structure and Function of the RedJ Protein, a Thioesterase from the Prodiginine Biosynthetic Pathway in Streptomyces coelicolor

Prodiginines are a class of red-pigmented natural products with immunosuppressant, anticancer, and antimalarial activities. Recent studies on prodiginine biosynthesis in Streptomyces coelicolor have elucidated the function of many enzymes within the pathway. However, the function of RedJ, which was predicted to be an editing thioesterase based on sequence similarity, is unknown. We report here the genetic, biochemical, and structural characterization of the redJ gene product. Deletion of redJ in S. coelicolor leads to a 75% decrease in prodiginine production, demonstrating its importance for prodiginine biosynthesis. RedJ exhibits thioesterase activity with selectivity for substrates having long acyl chains and lacking a β-carboxyl substituent. The thioesterase has 1000-fold greater catalytic efficiency with substrates linked to an acyl carrier protein (ACP) than with the corresponding CoA thioester substrates. Also, RedJ strongly discriminates against the streptomycete ACP of fatty acid biosynthesis in preference to RedQ, an ACP of the prodiginine pathway. The 2.12 Å resolution crystal structure of RedJ provides insights into the molecular basis for the observed substrate selectivity. A hydrophobic pocket in the active site chamber is positioned to bind long acyl chains, as suggested by a long-chain ligand from the crystallization solution bound in this pocket. The accessibility of the active site is controlled by the position of a highly flexible entrance flap. These data combined with previous studies of prodiginine biosynthesis in S. coelicolor support a novel role for RedJ in facilitating transfer of a dodecanoyl chain from one acyl carrier protein to another en route to the key biosynthetic intermediate 2-undecylpyrrole.

Phase tailored, potentiodynamically grown p -Cu 2−xTe/Cu layers

In this work we successfully prepared p-type semiconducting Cu 2− x Te layers on Cu substrates by applying a potential multistep signal. Spontaneously deposited tellurium layers were reduced in a single cathodic sweep. The X-ray diffraction characterization showed the presence of single-phased, crystalline Cu 2− x Te in the weissite form. A further anodization step allows crystallization of several phases such as Cu 1.75Te, Cu 0.664Te 0.336 and Cu 7Te 4. This type of sample was found to be photoactive. The prepared films are p-type and have carrier concentrations in the order of 10 21 cm −3, suitable for CdTe-Cu 2− x Te contacts.

The Valence Problem of Pd4Br4Te3

Pd(4)Br(4)Te(3) was prepared from Pd, Te, and PdBr(2) at 700 K. Its structure was determined by single-crystal X-ray diffraction to be triclinic, P$\bar 1$, Pearson symbol aP22; a=842.5(2), b=845.0(3), c=864.8(3) pm; alpha=82.55(3), beta=73.36(2), gamma=88.80(2) degrees ; Z=2. The Br and Te atoms are arranged according to the motif of cubic closest-packed spheres in which every 15th position is vacant; the Pd atoms occupy 8/15 of the octahedral voids. The symmetry relations with the packing of spheres are derived. Prominent structural units are hollow cuboctahedral [(PdBrTe)(6)] units, the Pd atoms are positioned near the centers of the square faces of the Br(6)Te(6) cuboctahedra; the cuboctahedra and double-octahedral Pd(2)Br(4)Te(6) units are connected to strands by sharing triangular Te(3) faces. The strands are condensed by common Br atoms into layered assemblies. Conspicuously close Te--Te contacts in the Te(3) triangles indicate attractive Te--Te interactions. The valence puzzle is resolved by the formula Pd(+II)(4)Br(-I)(4)Te(-4/3)(3). Positive Te--Te Mulliken orbital populations and the Pd--K, Br--K, and Te--L(III) XANES spectra of Pd(4)Br(4)Te(3) referenced to the spectra of PdBr(2), K(2)PdBr(6), PdTe, and PdTe(2) are in accord with attractive Te--Te interactions. The measured semiconducting and diamagnetic properties are compatible with the derived picture of chemical bonding in Pd(4)Br(4)Te(3).

Neutron and X-ray diffraction studies of TeCl4 and TeBr4 liquids

High-energy X-ray and neutron diffraction measurements have been carried out on TeCl4 and TeBr4 liquids just above their respective melting points. Both neutron SN(Q) and X-ray SX(Q) structure factors exhibit a pronounced first sharp diffraction peak (FSDP) at Q1(TeCl4)≈1.2Å-1 and Q1(TeBr4)≈1.1Å-1 indicating a significant intermediate range order in the two liquids. The complementarity between neutrons and X-rays allows the FSDP to be attributed to Te–Te correlations at a characteristic length scale L1≈2π/Q1≈5.3–5.7Å. The total correlation functions TN(r) and TX(r) show first nearest-neighbor distances at r1(TeCl4)≈2.36Å-1 and r1(TeBr4)≈2.54Å-1 in good agreement with a sum of covalent radii for Te, Cl or Br. The Te coordination was found to be nearly tetrahedral, 3.8⩽NTe–X⩽4.0, where X=Cl or Br. A distinct correlation at r2(TeCl4)≈2.75Å and r2(TeBr4)≈2.85Å was attributed to short nearest-neighbor Te–Te contacts. The respective coordination number, NTe–Te≈1, suggests a Te2X8 dimer to be the main structural unit in tellurium tetrahalide liquids, i.e., intermediate between tetrameric Te4X16 solid and monomeric TeX4 gas. This proposed short range order is consistent with intermediate range structure since the average molecular size of elliptic Te2Cl8 (≈5.4Å) and Te2Br8 (≈5.8Å) agrees with derived intermolecular separation and periodicity L1.

Thermoelectric properties of Nb 3Sb 2Te 5

Nb 3Sb 2Te 5 was prepared by reacting the elements in the respective stoichiometric ratios at 600 °C. Its crystal structure was re-determined via X-ray single crystal structure studies to check for Sb/Te ordering. In a prior study Nb 3Sb 2Te 5 was reported to crystallize in the Ir 3Ge 7 type, space group Im 3 ¯ m , with a = 9.8155(8) Å, with mixed Sb/Te occupancies. We found that complete Sb/Te ordering, which lowered the symmetry by removal of the inversion center, yielded improved residual factors, e.g. from R1 = 2.97% in Im 3 ¯ m ( a = 9.8180(4) Å) to R1 = 2.47% in I 4 ¯ 3 m . Because of this ordering, no Te–Te contacts <3.4 Å prevail. Electronic structure calculations predicted nonmetallic properties, which were verified by temperature-dependent conductivity studies. The investigation of the thermoelectric properties yielded at 300 K a Seebeck coefficient of −29 μV K −1, electrical conductivity of 75 Ω −1 cm −1, and thermal conductivity of 5.7 W m −1 K −1. The thermoelectric figure-of-merit improves rapidly with increasing temperature.

Investigation on the electrical properties of metal–Cd 0.9Zn 0.1Te contacts

The electrical properties of different metal–cadmium–zinc–telluride (CdZnTe) contacts produced by sputtering deposition method are investigated. The results of current–voltage and SEM analyses show that Au is the most suitable electrical contact material, which forms nearly ideal Ohmicity contact with high resistivity p-CdZnTe:In crystals and a 0.95 ± 0.02 eV barrier height with low resistivity ones. Passivation treatment can decrease the leakage current. XPS analyses show that Au atoms diffused into CdZnTe:In during annealing, meanwhile Cd and Te atoms diffuse into the Au contact. Diffused Au atoms do not form any compound with any element in CdZnTe:In crystal, but subsitute Cd sites or occupy Cd vacancies as acceptors. Thus, a heavy p-type doping layer is formed, and M–p +–p Ohmic contact is obtained.

A study of the reactivity of elemental Cr/Se/Te thin multilayers using X-ray reflectometry, in situ X-ray diffraction and X-ray absorption spectroscopy

The reactivity of [Cr/Se/Te] multilayers under annealing was investigated using X-ray reflectometry, in situ X-ray diffraction, X-ray absorption fine structure (XAFS) measurements and transmission electron microscopy. For all samples, interdiffusion was complete at temperatures between 100 and 300 °C, depending on the repeating tri-layer thickness. A crystalline phase nucleated approximately 20 °C above the temperature where interdiffusion was finished. The first crystalline phase in a binary Cr/Te sample was layered CrTe 3 nucleating at 230 °C. In ternary samples (Se:Te=0.6–1.2), the low-temperature nucleation of such a layered Cr Q 3 ( Q=Se, Te) phase is suppressed and instead the phase Cr 2 Q 3 nucleates first. Interestingly, this phase decomposes around 500 °C into layered Cr Q 3. In contrast, binary Cr/Se samples form stable amorphous alloys after interdiffusion and Cr 3Se 4 nucleates around 500 °C as the only crystalline phase. Evaluation of the XAFS data of annealed samples yield Se–Cr distances of 2.568(1) and 2.552(1) Å for Cr 2 Q 3 and Cr Q 3, respectively. In the latter sample, higher coordination shells around Se are seen accounting for the Se–Te contacts in the structure.

Effects of annealing on the properties of Au–Cd 0.9Zn 0.1Te contacts

Au–Cd 0.9Zn 0.1Te contacts were annealed for 10 min at 100, 200 and 300 °C, respectively. The effects of annealing have been analyzed with photoluminescence (PL) spectra, leakage current-bias voltage ( I– V) characteristic and leakage current–time ( I– t) characteristic. PL spectra indicate that there are more Au-related complexes and Cd vacancies (Zn vacancies) produced in Au–Cd 0.9Zn 0.1Te contacts during the annealing. These complexes and vacancies are responsible for the decrease of leakage current, which is revealed by I– V measurement, because they can trap free charge and improve the recombination rate of charge effectively. The I– V measurement also shows that the ohmic characteristic of Au–Cd 0.9Zn 0.1Te contacts is improved obviously by the annealing at 100 and 200 °C and deteriorated seriously by the annealing at 300 °C. In addition, I– t curves suggest that annealing can improve the stability of leakage current remarkably.

Molecular Conductors Based on peri‐Ditellurium‐Bridged Donors,2,3‐DMTTeA and TMTTeN

AbstractMolecular conductors based on peri‐ditellurium‐bridged polyacene donor molecules 3,4‐dimethylanthra[1,9‐cd:4,10‐c'd']bis[1,2]ditellurole (2,3‐DMTTeA) and 2,3,6,7‐tetramethylnaphtho[1,8‐cd:4,5‐c'd']bis[1,2]ditellurole (TMTTeN) were prepared. The crystal structure analyses of neutral 2,3‐DMTTeA molecule and its cation radical salts revealed that these crystals involve an orientational disorder of the asymmetrical molecule, 2,3‐DMTTeA, and that the intermolecular network through tellurium atoms is very strong and dominant in terms of the construction of the crystal frameworks. In the crystal of (TMTTeN)2M(CN)2 (M = Ag and Au), the crystal structure analyses and the extended Hückel tight‐binding band calculations indicated that these salts are quasi three‐dimensional conductors. These salts are highly conductive (720–760 S cm–1) and maintain metallic states down to about 50 K. Furthermore, the Ag(CN)2– salt exhibited a Pauli paramagnetic behavior down to 2 K [χ(para) ≈ 2.0–2.5 × 10–4 emu mol–1]. In the crystal of (TMTTeN)(SCN)0.88, the donor molecules are stacked to form one‐dimensional columns and construct a three‐dimensional network between the columns through the intermolecular Te···Te contacts. The SCN– salt is also highly conductive (590 S cm–1) and maintains a metallic behavior down to 4.2 K. Almost temperature‐independent paramagnetic susceptibility of (TMTTeN)(SCN)0.88 indicates Pauli paramagnetism of this salt[χ(para) ≈ 1.6–1.9 × 10–4 emu mol–1]. A tight‐binding band structure calculation indicates that the Fermi surface of the SCN– salt is open along the b* and c* directions, but the intermolecular interactions between the donor columns are not so weak because of the three‐dimensional networkmediated by the protruded tellurium atoms. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2005)

Synthesis and Crystal Structure of Tellurium(II) bis(2‐methoxycarbonylethanethiolate): A Novel Coordination Mode of Tellurium

AbstractThe tellurium(II) dithiolates Te[SCH2CH2C(O)OCH3]2, (1), Te[SCH2CH2CH2SC(O)CH3]2, (2), and Te[SCH2CH2CH2CH2SC(O)CH3]2, (3) were synthesized from Te(StBu)2 and the corresponding thiol. All compounds are sensitive toward higher temperatures and light and decompose to elemental tellurium and the disulfide. In the solid state, the Te atom of 1 exhibits the novel Te(S2Te2) coordination mode. Additionally to the two Te—S bonds, each Te atom forms two long Te···Te contacts to neighboring molecules, leading to a coordination number of four and a distorted sawhorse configuration. No intramolecular Te···O interactions are present in the solid state, in accordance with ab initio calculations (MP2/ecp‐basis) for the isolated molecule. 125Te NMR shifts of all compounds lay within a narrow range and close to the respective shift of other Te(SCH2R)2 compounds. VT 125Te NMR spectra gave no hint to donor acceptor interactions in solution for any of the compounds and thus corroborate results from IR‐spectroscopy, ab initio geometry optimizations, and thermochemical calculations.

Adducts of Tellurium Tetrachloride with Allyl Alcohol and Allyl Acetate: 1,2- vs 1,3-Addition and Structure and Dynamics of Te···O Interactions in Different Phases

The compounds Cl3Te[CH2CH(Cl)CH2O(H)···]·Cl2Te[−CH2CH(Cl)CH2O−] (1) and Cl3Te[CH2CH(CH2Cl)OC(CH3)O···] (2) were prepared by the reaction of TeCl4 with allyl alcohol and allyl acetate, respectively. Their molecular and crystal structures were investigated by single-crystal X-ray analysis, 1H−1H-NOESY experiments, IR spectroscopy, and ab initio geometry optimization. 1 is a composite compound, whose subunits Cl2Te[−CH2CH(Cl)CH2O−] (1A) and Cl3Te[CH2CH(Cl)CH2O(H)···] (1B) are linked in the solid state via Te···Cl−Te and O···H−O bridges. Both Te atoms are involved in similar five-membered rings, having a covalent Te−O bond in one case (1A) and a dative Te···O bond in the other (1B). In the solid state, both Te atoms are pentacoordinate with pseudo-octahedral configurations. Formation of 2 is accompanied by a 3,2-migration of the acetate group, leading to a 1,3-addition of TeCl4 to allyl acetate and a six-membered ring via an intramolecular dative Te···O interaction. In the solid state, single molecules of 2 are linked by weak CH2Cl···Te contacts, the Te atom being hexacoordinate with a distorted-octahedral configuration. Since reaction of 1 with acetyl chloride also gives 2, the 1,3-addition product of TeCl4 with allyl acetate must be thermodynamically more stable than the corresponding 1,2-addition product, a conclusion that is supported by ab initio calculations. Ab initio calculations (MP2/LANL2DZP) for Cl3Te[CH2CH(Cl)CH2O(H)···] (1B) and 2 revealed strong n(O)−σ*(Te−Cl) and Coulombic interactions for the Te···O bonds, which are significantly longer in the isolated molecules than in the solid state. Multinuclear NMR spectroscopy and 1H−1H-NOESY experiments show the cyclic structures to exist in solution as well, with little changes in their geometry compared to the solid state.

Key Aspects of CdTe/CdS Solar Cells

Recent developments in the following areas are briefly reviewed: a) the electrical structure of grain boundaries in CdTe absorbers, b) impurities and non-stoichiometry in CdTe solar cells and c) use of Sb2Te3 in contacts to CdTe. Nominally identical solar cells fabricated using 99.999% pure CdTe feedstock from two different suppliers were compared. Differences in the photovoltaic response and absorber grain size were correlated with the purity of the feedstock, the purer material giving the higher Voc, FF and efficiency, and larger grain size. Quantum efficiency and C–V measurements indicated that the performance differences are most likely to result from reduced doping at the back contact surface in the less pure sample. A quantitative SIMS study of Sb–Te contacts to CdTe reveals that annealing in air at 400 °C causes an influx of Sb and O into the absorber layer. Free energy calculations indicate that this is driven by the preferential reaction of O with Sb compared to CdTe oxidation.

Clustering of Zirconium Atoms in Zr5Te6: A Novel NiAs-Type-Related Telluride with Ordered Vacancies

Zr5Te6 has been synthesized and its structure determined by means of single crystal X-ray diffraction to be trigonal, , Z=3, Pearson symbol hP33, a=1172.8(2) pm, c=707.0(1) pm. Zr5Te6 adopts a metal-deficient, vacancy-ordered 3a×3a×1c superstructure of the NiAs type structure. In the Zr atom layers, alternately one and two out of nine Zr atoms are missing. The less densely populated layers (7/9) consist of star-shaped Zr7 clusters with intracluster contacts of 351.1 pm; the shortest Zr–Zr intercluster distance is 470.5 pm. In the more densely populated Zr atom layers (8/9), three quarters of the Zr atoms are arranged to pairs (326.4 pm). The distinctive distribution of the vacancies affords a topologically uniform fivefold Zr coordination (283.5–302.6 pm) for all three crystallographically inequivalent Te atoms. They are shifted towards the vacancies in the Zr atom layers. The associated corrugation of the Te atom layers is characterized by an amplitude of 28 pm. The Te–Te contacts are ≥368.1 pm. According to extended Huckel calculations, the defects in the Zr atom layers lead to a reduction in overall Zr–Te bonding interactions relative to ZrTe (NiAs). However, through the clustering the total attractive intralayer Zr–Zr interactions increase considerably, thus providing decisive stabilization of the structure. As revealed by thermal analyses, Zr5Te6 undergoes a reversible phase transition at 1513±5 K. On the Zr-rich side, Zr5Te6 coexists with ZrTe (WC), and, above 1438±5 K with the hitherto unknown ZrTe (MnP). Zr5Te6 exhibits temperature independent paramagnetic properties (χmol=0.7×10−3 cm3 mol−1) that are typical for a metallic conductor. An abrupt increase in the magnitude of the diamagnetic susceptibility below 2.2 K in a weak magnetic field indicates a superconducting transition.

The Solid State Conformation of Diaryl Ditellurides and Diselenides: The Crystal and Molecular Structures of (C4H3E2)2E'2 (E = O, S; E' = Te, Se)

The crystal and molecular structures of dithienyl ditelluride (C4H3S)2Te2 (1), difuryl ditelluride (C4H3O)2Te2 (2), dithienyl diselenide (C4H3S)2Se2 (3), and difuryl diselenide (C4H3O)2Se2 (4) are reported in this paper and compared to those of other simple diaryl ditellurides and diselenides. The chalcogen-chajcogen bonds exhibit approximately single bond lengths [Te-Te = 2.7337(8) and 2.7240(4) Å in 1 and 2, respectively; Se-Se = 2.357(1) and 2.368(2) Å in 3 and 4, respectively], as do the chalcogen-carbon bond lengths [Te-C = 2.095(9) - 2.104(6) in 1 and 2.091(6) - 2.105(9) Å in 2; Se-C = 1.87(1) - 1.90(1) Å in 3 and 1.887(8) - 1.897(10) Å in 4]. The aromatic rings are disordered. The dihedral angles C-E-E-C range from 79(2) to 96(1)° are consistent with the concept of minimized p lone-pair repulsion of adjacent chalcogen atoms. The dependence of molecular parameters on the angle between the aromatic rings and the chalcogen-chalcogen bonds follow trends established previously for aromatic disulfides. Though the bond parameters and conformations of 1 - 4 are similar, the packing of the molecules is different. The two ditellurides 1 and 2 show short Te···Te contacts (3.900 - 4.002 Å in 1 and 4.060 - 4.172 Å in 2). The two diselenides 3 and 4 do not exhibit close chalcogen-chalcogen interactions. The NMR spectroscopic properties of 1 - 4 are discussed.

The crystal structure of synthetic buckhornite, [Pb2BiS3][AuTe2

Synthetic buckhornite, [Pb2BiS3][AuTe2], was grown from melts in connection with the search for high-temperature superconductive materials. Chemical analyses were performed by electron-microprobe investigations. The crystal structure was determined from 726 single-crystal X-ray reflections of a twinned crystal. The refinement gave R(F)=0.101 for 33 variable parameters. The space group is Pmmn, a=4.108(3) Å, b=12.308(9) Å, c=9.331(6) Å, Z=2. The atomic arrangement features a pronounced layer structure formed by two different sheets. (a) Planar Au[4Te]Te4 configurations are edge-connected to ribbons in [100]; they are linked by Te···Te contacts to planar nets parallel to (001). Te and Au atoms are in a distorted square arrangement. (b) Slices of (Pb,Bi)S are sandwiched between these AuTe2 layers. They form SnS-archetype layers. The present paper proves that buckhornite, [(Pb2Bi)Σ3S3] [(Te2Au)Σ3], and nagyagite, [(Pb3(Pb,Sb)3)Σ6S6][(Te,Au)3] are members of a homologous series. Both compounds have comparable Au—Te layers. However, ordering of Au and Te atoms was verified in buckhornite only. In buckhornite two (Pb,Bi)S sheets form one slice of the SnS-archetype whereas in nagyagite four (Pb,Sb)S layers form the corresponding slice with a thickness of two SnS-archetype slabs.