pinecone/core-2020-05-10-deduplication huggingface dataset:
Employment and Careers of European Chemists (ESEC2)

Employment conditions and career opportunities are in the focus of the new Employment Survey for European Chemists (ESEC2). Conditions and opportunities are individually analysed for all countries with a statistically significant number of responses. The results provide important clues for careers in these countries and in Europe as a whole. The importance of employer sectors varies very much between European countries. A chapter of this report is devoted to career planning of students and new graduates. This is the first general evaluation of the survey. It provides many details about the chemistry workforce in Europe and its development.Publisher PDFPeer reviewe
Weak pnictogen bond with bismuth : experimental evidence based on Bi-P through-space coupling.

To study pnictogen bonding involving bismuth, flexible accordion‐like molecular complexes of the composition [P(C6H4‐o‐CH2SCH3)3BiX3], (X=Cl, Br, I) have been synthesised and characterised. The strength of the weak and mainly electrostatic interaction between the Bi and P centres strongly depends on the character of the halogen substituent on bismuth, which is confirmed by single‐crystal X‐ray diffraction analyses, DFT and ab initio computations. Significantly, 209Bi–31P through‐space coupling (J=2560 Hz) is observed in solid‐state 31P NMR spectra, which is so far unprecedented in the literature, delivering direct information on the magnitude of this pnictogen interaction
Phosphorus Nitride P3N5

Pure, stoichiometric, hydrogen-free, and crystalline phosphorus nitride P3N5 has been obtained for the first time by reaction of (PNCl2)3 and NH4Cl between 770 and 1050 K. The compound has been characterized by elemental analyses, 31P and 15N MAS NMR, EXAFS, IR spectroscopy, X-ray powder diffraction, and electron microscopy. In the solid a three-dimensional cross-linked network structure of corner sharing PN4 tetrahedra has been identified with 2/5 of the nitrogen atoms bonded to three P atoms and 3/5 of the nitrogen atoms bonded to two P atoms. By electron diffraction (ED) and high-resolution transmission electron microscopy (HRTEM) two distinguishable modifications α-P3N5 and β-P3N5 have been identified which differentiate only by the stacking order of identical sheets similar to the polytypes of SiC.
Mesogenic sugars. From aldoses to liquid crystals and surfactants

Amphiphilic sugar derivatives, formed by condensation of functionalized aliphatic chains with aldoses, form liquid crystals, in most cases smectic. A puzzling observation was the failure of the S,S-acetals of 6-deoxy sugars, L-rhamnose and D-fucose, to form such phases. A satisfactory model to explain this behavior involves—in most cases—the formation of columns, which are destabilized with the deoxy sugars in which the apolar end methyl groups are pushed together.
Despite the abundance of chiral centers in the mono- and disaccharides used the smectic phases themselves in general display no chirality. By appropriate molecular design in which the amphiphilic character was deliberately suppressed it was possible to prepare glucose derivatives that exhibit chiral nematic phases as well as impressive helical twisting powers. Simple condensation chemistry is used to produce such derivatives.
The amphiphilic character can be deliberately enhanced, and this is readily achieved in double headed ‘gemini’ derivatives formed by condensation of glucose or lactose with a long chain diamine followed by reduction followed by acylation of the nitrogen atoms with long chain acyl anhydrides. The thermodynamics of micellization of precursors to these derivatives have been studied. The gemini derivatives themselves display remarkable properties including the formation of giant vesicles and an appreciable capacity for the solubilization of hydrocarbons.
A Theoretical and Experimental Study on the Lewis Acid−Base Adducts (P4E3)·(BX3) (E = S, Se; X = Br, I) and (P4Se3)·(NbCl5)

The Lewis acid−base adducts (P4E3)·(BX3) (E = S, Se; X = Br, I) and (P4Se3)·(NbCl5) have been prepared and characterized by Raman, IR, and solid-state 31P MAS NMR spectroscopy. Hybrid density functional calculations (B3LYP) have been carried out for both the apical and the basal (P4E3)·(BX3) (E = S, Se; X = Br, I) adducts. The thermodynamics of all considered species has been discussed. In accordance with solid-state 31P MAS NMR and vibrational data, the X-ray powder diffraction structures of (P4S3)·(BBr3) [monoclinic, space group P21/m (No. 11), a = 8.8854(1) Å, b = 10.6164(2) Å, c = 6.3682(1) Å, β = 108.912(1)°, V = 568.29(2) Å3, Z = 2] and (P4S3)·(BI3) [orthorhombic, space group Pnma (No. 62), a = 12.5039(5) Å, b = 11.3388(5) Å, c = 8.9298(4) Å, V = 1266.09(9) Å3, Z = 4] indicate the formation of an apical P4S3 complex in the reaction of P4S3 with BX3 (X = Br, I). Basal adducts are formed when P4Se3 is used as the donor species. Vibrational assignment for the normal modes of these adducts has been made on the basis of comparison between theoretically obtained and experimentally observed vibrational data.
A Suzuki Coupling Based Route to 2,2'-Bis(2-indenyl)biphenyl Derivatives

Because of the promising performance in olefin polymerization of 2,2'-bis(2-indenyldiyl)biphenyl zirconium dichloride, we developed a new and broadly applicable route to 2,2'-bis(2-indenyl)biphenyl derivatives. Reaction of the known 2,2'-diiodobiphenyl with the new 2-indenyl boronic acid did not result in the desired 2,2'-bis(2-indenyl)biphenyl (10); instead an isomer thereof, (spiro-1,1-(2,2'-biphenyl)-2-(2-indenyl)indane), was obtained. It was found that compound 10 could be made via a palladium-catalyzed reaction of 2,2-biphenyldiboronic acid with 2-bromoindene under standard Suzuki reaction conditions. However, the yield of this reaction was low at low palladium catalyst loadings, due to a competitive hydrolysis reaction of 2,2-biphenyldiboronic acid. HTE techniques were used to find an economically viable protocol. Thus, use of the commercially available 1.0 molar solution of (n-Bu)4NOH in methanol with cosolvent toluene led to precipitation of the pure product in a fast and clean reaction, using only 0.7 mol % (0.35 mol % per C-C) of the expensive palladium catalyst.
The Synthesis, Structure and Physical Properties of the Layered Ruthenocuprates RuSr2GdCu2O8 and Pb2Sr2Cu2RuO8Cl

Studies of the structure and physical properties of the layered rutheno- cuprates RuSr2GdCu2O8 and Pb2Sr2Cu2RuO8Cl are reviewed. RuSr2GdCu2O8 is a weak ferromagnetic superconductor and doping studies have shown that it is possible to tune the magnetic and superconducting transitions simultaneously. The average crystal structure of RuSr2GdCu2O8 is tetragonal at both 10 and 295 K (space group P4/mmm), but a sq.root2a x sq.root2a x c superstructure resulting from coherent rotations of the RuO6 octahedra within subdomains of 50-200 ºA is observed by selected area electron distraction (SAED). The same tilts and rotations of the RuO6 octahedra are observed in semiconducting Pb2Sr2Cu2RuO8Cl, which has strikingly similar magnetic properties to RuSr2GdCu2O8. Antiferromagnetic order is observed in the 10 K neutron diffraction pattern with a Ru moment of 1.1(1) B, but a spin-flop transition is observed above a field of 0.5 T
Spin-orbit coupling and electron spin resonance for interacting electrons in carbon nanotubes

We review the theoretical description of spin-orbit scattering and electron spin resonance in carbon nanotubes. Particular emphasis is laid on the effects of electron-electron interactions. The spin-orbit coupling is derived, and the resulting ESR spectrum is analyzed both using the effective low-energy field theory and numerical studies of finite-size Hubbard chains and two-leg Hubbard ladders. For single-wall tubes, the field theoretical description predicts a double peak spectrum linked to the existence of spin-charge separation. The numerical analysis basically confirms this picture, but also predicts additional features in finite-size samples
New Thiocarbonyl Ylides derived from 3,3-Dichloro-2,2,4,4-tetramethylcyclobutanethione; Generation and reactions

The reaction of 3,3-dichloro-2,2,4,4-tetramethylcyclobutanethione (1) with diazo compounds yielded spirocyclic 2,5-dihydro-1,3,4-thiadiazoles 3, which decomposed at ca. 45°C to give the corresponding thiocarbonyl ylide of type 4. In the absence of trapping agents, these thiocarbonyl ylides underwent a 1,3-dipolar electrocyclization to yield spirocyclic thiiranes 5. On the other hand, the thiocarbonyl methanide 4a was efficiently intercepted with C C, C=C, C=O, C=S, and N=N dipolarophiles leading to the [2+3] cycloadducts. A non-stereoselective cycloaddition took place when 3a was decomposed\ud
in the presence of the very electron-deficient dicyanofumarate or maleate, indicating a two step mechanism via an intermediate zwitterion. Furthermore, the thiocarbonyl methanide 4a could be trapped by the imidazole-2-thione 7 to give the 1,3-adduct 8. Treatment of 3a with secondary amines led to amidrazones of type 25 via base-catalyzed ring opening and condensation reaction
Synthesis and Characterization of Tb[N(CN)2]3·2H2O and Eu[N(CN)2]3·2H2O:

Two new rare-earth dicyanamides, namely, Tb[N(CN)2]3·2H2O and Eu[N(CN)2]3·2H2O, have been prepared by ion exchange in aqueous solution, followed by evaporation of the solvent at room temperature. The structures of both compounds have been solved and refined from single-crystal and powder X-ray diffraction data, respectively. The two compounds are isostructural and are built up from irregular quadratic antiprismatic LnN6O2 polyhedra connected to each other by three crystallographically independent dicyanamide ([N(CN)2]3-) ions (Tb[N(CN)2]3·2H2O, P21/n, Z = 4, a = 7.4632(15) Å, b = 11.523(2) Å, c = 13.944(3) Å, β = 94.06(3)°, V = 1196.2(4) Å3; Eu[N(CN)2]3·2H2O, P21/n, Z = 4, a = 7.4780(3) Å, b = 11.5429(5) Å, c = 13.9756(7) Å, β = 93.998(4)°, V = 1203.41(10) Å3). Annealing of the hydrated phases of Ln[N(CN)2]3·2H2O (Ln = Eu, Tb) at 150 °C under an argon atmosphere leads to the formation of nonhydrated Ln[N(CN)2]3 (Ln = Eu, Tb). Both the hydrated (Eu[N(CN)2]3·2H2O) and nonhydrated (Eu[N(CN)2]3) europium(III) dicyanamides show red luminescence due to the dominant intensity of 5D0−7FJ (J = 1, 2, 4) emission lines by excitation at 365 nm. The broad excitation band of europium(III) dicyanamide (fwhm = 8000 cm-1) ranging between 260 and 420 nm with λmax ≈ 30000 cm-1 is ascribed to a Eu−N charge-transfer transition, which is significantly shifted to lower energy compared to that of oxo compounds due to the nephalauxetic effect. Similarly, both the hydrated (Tb[N(CN)2]3·2H2O) and nonhydrated (Tb[N(CN)2]3) terbium(III) dicyanamides show green emission at λexc = 365 nm, arising mainly from the dominant 5D0−7F4 transition. However, unlike europium(III) dicyanamide, the broad excitation band of terbium(III) dicyanamide ranging between 250 and 400 nm with a maximum at 33000 cm-1 can be assigned to the 4f8−4f75d1 transition of Tb3+.
Color Point Tuning for (Sr,Ca,Ba) Si2O2N2:Eu2+ for White Light LEDs

Color point tuning is an important challenge for improving white light LEDs. In this paper, the possibilities of color tuning with the efficient LED phosphor Sr1−x−y−zCaxBaySi2O2N2:Euz2+ (0 ≤ x, y ≤ 1; 0.005 ≤ z ≤ 0.16) are investigated. The emission color can be tuned in two ways: by changing Eu2+ concentration and by substitution of the host lattice cation Sr2+ by either Ca2+ or Ba2+. The variation in the Eu2+ concentration shows a red shift of the emission upon increasing the Eu concentration above 2%. The red shift is explained by energy migration and energy transfer to Eu2+ ions emitting at longer wavelengths. Along with this (desired) red shift there is an (undesired) lowering of the quantum efficiency and the thermal quenching temperature due to concentration quenching. Partial substitution of Sr2+ by either Ca2+ or Ba2+ also results in a red-shifted Eu2+ emission. For Ca2+ this is expected and the red shift is explained by an increased crystal field splitting for Eu2+ on the (smaller) Ca2+ cation site. For Ba2+, the red shift is surprising. Often, a blue shift of the fd emission is observed in case of substitution of Sr2+ by the larger Ba2+ cation. The Eu2+ emission in the pure BaSi2O2N2 host lattice is indeed blue-shifted. Temperature dependent luminescence measurements show that the quenching temperature drops upon substitution of Sr by Ca, whereas for Ba substitution, the quenching temperature remains high. Color tuning by partial substitution of Sr2+ by Ba2+ is therefore the most promising way to shift the color point of LEDs while retaining the high quantum yield and high luminescence quenching temperature.
Low Temperature Precursor Route for Highly Efficient Spherically Shaped LED-Phosphors M2Si5N8:Eu2+ (M = Eu, Sr, Ba)

The highly efficient nitridosilicate phosphors M2Si5N8 (M = Sr, Ba, Eu) for phosphor-converted pc-LEDs were synthesized at low temperatures using a novel precursor route involving metal amides M(NH2)2. These precursors have been synthesized by dissolution of the respective metals in supercritical ammonia at 150°C and 300 bar. The thermal behavior and decomposition process of the amides were investigated with temperature programmed powder X-ray diffractometry and thermoanalytical measurements (DTA/TG). These investigations rendered the amides as suitable intermediates for reaction with silicon diimide (Si(NH)2). Thus, the desired nitridosilicate phosphors were obtained at relatively low temperatures around 1150−1400°C which is approximately 300°C lower compared to common synthetic approaches starting from metals or oxides. The influence of the thermal treatment on the phosphor morphology has been studied extensively. The accessibility of spherical phosphor particles represents another striking feature of this route since it improves light extraction from the crystallites due to decreasing light guiding and decreasing re-absorption inside the phosphor particle. The synthesized luminescent materials M2Si5N8:Eu2+ (M = Sr, Ba) exhibit quantum efficiencies and emission band widths (FWHM 70−90 nm) comparable to standard phosphor powders. Employment of Eu(NH2)2 as dopant reagent for synthesis of Ba2Si5N8:Eu2+ proved favorable for the formation of spherical crystallites compared to doping with Eu metal, halides, or oxide.
One-Pot Synthesis of Single-Source Precursors for Nanocrystalline LED Phosphors M2Si5N8:Eu2+ (M = Sr, Ba)

Highly efficient red-emitting nitridosilicate phosphors Sr2Si5N8:Eu2+ and Ba1.5Sr0.5Si5N8:Eu2+ (doping level 1%) applicable to phosphor converted pc-LEDs were synthesized in nanocrystalline form at low temperatures employing a novel single-source precursor approach. Synthesis starts from nanocrystalline silicon and uses mixed metal amides M(NH2)2 with M = Sr, Ba, Eu as reactive intermediates. In a second approach, a single-source precursor mixture obtained from a one-pot reaction of the corresponding elements (Sr/Ba, Eu, Si) was obtained in supercritical ammonia. Thermoanalytical in situ investigations gain a deeper insight into the degradation mechanism of the mixed metal amide precursors and revealed the onset for the formation of the 2-5-8 phosphor materials at temperatures slightly above 900°C. Formation of the products is complete below 1400°C. Under these conditions, the nitridosilicate phosphors form spherically shaped particles with crystallites of 200 nm in size. Spherical particles are desirable for phosphor application because light extraction may be improved by decreased light trapping and re-absorption losses. As a major advantage of the one-pot precursor approach, the exact Sr/Ba content in the solid solution series Sr2−xBaxSi2N8:Eu2+ and the doping concentration of Eu2+ can easily be controlled in a wide range by the relative amount of the elemental starting materials (Sr, Ba, Eu, Si). Simultaneously, thorough mixing of these elements down to an atomic level (Sr, Ba, Eu) or at least at nanoscopic dimensions (silicon) is achieved by the solution approach. As a consequence, no milling and pre-reaction steps are necessary which might give rise to contamination. Advantageously, this approach can easily be extended to large-scale processes by simultaneously preserving complete mixing. Furthermore, the influence of the starting materials (single-source precursor, nanocrystalline silicon) and the reaction conditions on the crystal shape and finally on the luminescence properties of the products was investigated. The obtained nanophosphors exhibit luminescence properties comparable to coarsely crystalline nitridosilicate phosphor powders prepared by conventional high-temperature processing.
Mixed Valence Europium Nitridosilicate Eu2SiN3

The mixed valence europium nitridosilicate Eu2SiN3 has been synthesized at 900°C in welded tantalum ampules starting from europium and silicon diimide Si(NH)2 in a lithium flux. The structure of the black material has been determined by single-crystal X-ray diffraction analysis (Cmca (no. 64), a=542.3(11) pm, b=1061.0(2) pm, c=1162.9(2) pm, Z=8, 767 independent reflections, 37 parameters, R1=0.017, wR2=0.032). Eu2SiN3 is a chain-type silicate comprising one-dimensional infinite nonbranched zweier chains of corner-sharing SiN4 tetrahedra running parallel [100] with a maximum stretching factor fs=1.0. The compound is isostructural with Ca2PN3 and Rb2TiO3, and it represents the first example of a nonbranched chain silicate in the class of nitridosilicates. There are two crystallographically distinct europium sites (at two different Wyckoff positions 8f) being occupied with Eu2+ and Eu3+, respectively. 151Eu Mössbauer spectroscopy of Eu2SiN3 differentiates unequivocally these two europium atoms and confirms their equiatomic multiplicity, showing static mixed valence with a constant ratio of the Eu2+ and Eu3+ signals over the whole temperature range. The Eu2+ site shows magnetic hyperfine field splitting at 4.2 K. Magnetic susceptibility measurements exhibit Curie-Weiss behavior above 24 K with an effective magnetic moment of 7.5 μB/f.u. and a small contribution of Eu3+, in accordance with Eu2+ and Eu3+ in equiatomic ratio. Ferromagnetic ordering at unusually high temperature is detected at TC=24 K. DFT calculations of Eu2SiN3 reveal a band gap of ∼0.2 eV, which is in agreement with the black color of the compound. Both DFT calculations and lattice energetic calculations (MAPLE) corroborate the assignment of two crystallographically independent Eu sites to Eu2+ and Eu3+.
Ca3N2 and Mg3N2: Unpredicted High-Pressure Behavior of Binary Nitrides

High-pressure synthesis allows both fundamental and materials science research to gain unprecedented insight into the inner nature of materials properties at extreme environment conditions. Here, we report on the high-pressure synthesis and characterization of γ-Ca3N2 and the high-pressure behavior of Mg3N2. Investigation of M3N2 (M=Ca, Mg) at high-pressure has been quite challenging due to the high reactivity of these compounds. Ex situ experiments have been performed using a multianvil press at pressures from 8 to 18 GPa (1000-1200 °C). Additional in situ experiments from 0 to 6 GPa (at RT) at the multianvil press MAX 80 (HASYLAB, Beamline F.2.1, Hamburg) have been carried out. The new cubic high-pressure phase γ-Ca3N2 with anti-Th3P4 defect structure exhibits a significant increase in coordination numbers compared to R-Ca3N2. Contrary, Mg3N2 shows decomposition starting at surprisingly low pressures, thereby acting as a precursor for Mg nanoparticle formation with bcc structure. Soft X-ray spectroscopy in conjunction with first principles DFT calculations have been used to explore the electronic structure and show that γ-Ca3N2 is a semiconductor with inherent nitrogen vacancies.
Synthesis of enantioenriched sulfoxides

This review discusses strategies for the asymmetric synthesis of sulfoxides, compounds with many applications in stereoselective synthesis and in some cases with pharmaceutical application. The review describes asymmetric oxidation, including metal catalyzed and non-metal and biological oxidation processes, in addition to synthetic approaches via nucleophilic substitution of appropriately substituted precursors. Kinetic resolution in oxidation of sulfoxides to the analogous sulfones is also discussed; in certain instances, access to enantioenriched sulfoxides can be achieved via a combination of asymmetric sulfide oxidation and complementary kinetic resolution in sulfoxide oxidation
Unprecedented Zeolite-Like Framework Topology Constructed from Cages with 3-Rings in a Barium Oxonitridophosphate

A novel oxonitridophosphate, Ba19P36O6+xN66-xCl8+x(x≈4.54), has been synthesized by heating a multicomponent reactant mixture consisting of phosphoryl triamide OP(NH2)3, thiophosphoryl triamide SP(NH2)3, BaS, and NH4Cl enclosed in an evacuated and sealed silica glass ampule up to 750°C. Despite the presence of side phases, the crystal structure was elucidated ab initio from high-resolution synchrotron powder diffraction data (λ=39.998 pm) applying the charge flipping algorithm supported by independent symmetry information derived from electron diffraction (ED) and scanning transmission electron microscopy (STEM). The compound crystallizes in the cubic space group Fm3c (no. 226) with a = 2685.41(3) pm and Z = 8. As confirmed by Rietveld refinement, the structure comprises all-side vertex sharing P(O,N)4 tetrahedra forming slightly distorted 3846812 cages representing a novel composite building unit (CBU). Interlinked through their 4-rings and additional 3-rings, the cages build up a 3D network with a framework density FD = 14.87 T/1000 Å3 and a 3D 8-ring channel system. Ba2+ and Clˉ as extra-framework ions are located within the cages and channels of the framework. The structuralmodel is corroborated by 31P double-quantum(DQ) /single-quantum (SQ) and triple-quantum (TQ) /single-quantum (SQ) 2D correlation MAS NMR spectroscopy. According to 31P{1H} C-REDOR NMR measurements, the H content is less than one H atom per unit cell.
Ba3Ga3N5 - A Novel Host Lattice for Eu2+ - Doped Luminescent Materials with Unexpected Nitridogallate Substructure

The alkaline earth nitridogallate Ba3Ga3N5 was synthesized from the elements in a sodium flux at 760°C utilizing weld shut tantalum ampules. The crystal structure was solved and refined on the basis of single-crystal X-ray diffraction data. Ba3Ga3N5 (space group C2/c (No. 15), a = 16.801(3), b = 8.3301(2), c = 11.623(2) Å, β = 109.92 (3)°, Z = 8) contains a hitherto unknown structural motif in nitridogallates, namely, infinite strands made up of GaN4 tetrahedra, each sharing two edges and at least one corner with neighboring GaN4 units. There are three Ba2+ sites with coordination numbers six or eight, respectively, and one Ba2+ position exhibiting a low coordination number 4 corresponding to a distorted tetrahedron. Eu2+ - doped samples show red luminescence when excited by UV irradiation at room temperature. Luminescence investigations revealed a maximum emission intensity at 638 nm (FWHM =2123 cm−1). Ba3Ga3N5 is the first nitridogallate for which parity allowed broadband emission due to Eu2+ - doping has been found. The electronic structure of both Ba3Ga3N5 as well as isoelectronic but not isostructural Sr3Ga3N5 was investigated by DFT methods. The calculations revealed a band gap of 1.53 eV for Sr3Ga3N5 and 1.46 eV for Ba3Ga3N5.