A new approach for quantifying ecological sustainability in waste management by using the method of modelling.

Human activity has an ever-increasing impact on the environment. In order to understand all processes and interactions behind this change, one has to analyze the environmental impact. Life Cycle Assessments (LCAs) are one way to achieve this, which, however, are time-consuming and often associated with high costs, as well as the requirement of specialized knowledge and software. This paper introduces a model, which allows an initial assessment. The model enables a more pragmatic way and may be considered as a first step in order to implement ecological sustainability considerations into companies. Based on a real-world problem, namely the disposal of foundry dust, the model is explained in a vivid manner.

Intrinsic Anomalous Hall Effect in Ni-Substituted Magnetic Weyl Semimetal Co3Sn2S2.

Topological Weyl semimetals have recently attracted considerable attention among materials scientists as their properties are predicted to be protected against perturbations such as lattice distortion and chemical substitution. However, any experimental proof of such robustness is still lacking. In this study, we experimentally demonstrate that the topological properties of the ferromagnetic kagomé compound Co3Sn2S2 are preserved upon Ni substitution. We systematically vary the Ni content in Co3Sn2S2 single crystals and study their magnetic and anomalous transport properties. For the intermediate Ni substitution, we observe a remarkable increase in the coercive field while still maintaining significant anomalous Hall conductivity. The large anomalous Hall conductivity of these compounds is intrinsic, consistent with first-principles calculations, which proves its topological origin. Our results can guide further studies on the chemical tuning of topological materials for better understanding.

Synthesis, Crystal Structure, and Selected Properties of [Au(S2 CNH2 )2 ]SCN: A Precursor for Gold Macro-Needles Consisting of Gold Nanoparticles Glued by Graphitic Carbon Nitride.

A new preparation route is developed for the synthesis of needle-like crystals of [Au(S2 CNH2 )2 ]SCN, which avoids disproportionation of the AuI salt used as a starting material. In the crystal structure, the two crystallographically independent AuIII centers are in a square-planar environment of two S2 CNH2 ligands. The Hirshfeld surface analysis reveals the presence of noncovalent intermolecular S⋅⋅⋅S interactions, which are essential for the spatial arrangement of the molecules. Density functional theory (DFT) calculations including dispersion and damping corrections result in a unit cell volume very close to the value determined experimentally. Thermal decomposition in an inert atmosphere generates black needles with lengths of up to 500 µm. X-ray powder diffraction and pair distribution function analyses demonstrate that the needles are composed of nanosized crystals with a volume-weighted average domain size of 20(1) nm. According to results of X-ray photoemission experiments, the black needles are covered by a nitrogen-rich carbon nitride with composition near (CN)2 N. 13 C solid-state NMR investigations indicate that two different carbon species are present, with signals corresponding well to heptazine units as in melon and triazine units as in poly(triazin imide) type compounds. Scanning transmission electron microscopy tomography evidences that the needles are composed of slightly elongated nanoparticles.

From Laboratory Press to Spins with Giant Effects.

Parallelly aligned spins in Co-Kagome nets have provided several reasons for researchers to celebrate: Liu et al. and Wang et al. have reported discoveries of unique combinations of properties: Sn2 Co3 S2 =Co3 Sn2 S2 =SnCo3/2 S exhibits giant anomalous Hall effects that exceed those of known materials by orders of magnitude. For this laboratory curiosity, a specific electronic topology has been discovered in the predicted half-metal ferromagnetic S= 1 / 2 state that makes it a fascinating example of the novel group of magnetic Weyl semimetals. We present a chemical view on this compound that was little understood for a long time, but that is now also studied with respect to skyrmion lattices and thermoelectrics.

The First Alkaline-Earth Fluorooxoborate Ba[B4 O6 F2 ]-Characterisation and Doping with Eu2.

The very first alkaline-earth fluorooxoborate Ba[B4 O6 F2 ] was synthesised by solid state methods starting from Ba(BF4 )2 , ß-BaB2 O4 , and B2 O3 . The crystal structure derived from single-crystal X-ray diffraction (P21 /n, a=6.6384(2) Å, b=7.6733(3) Å, c=11.3385(4) Å, ß=91.281(2)°, Z=4, Rint =0.0269, R1 =0.018, wR2 =0.034) comprises layers of BO3 F tetrahedra condensed through triangular BO3 units according to the descriptor 2Δ2□:<Δ2□>Δ. The extraordinary thirteen-fold coordination of barium by oxygen and fluorine leads to interesting optical properties of a sample doped with divalent europium, where a 4f→4f emission was recorded around 359 nm together with a broad emission band of a 5d→4f emission peaking at 366 nm. The compound is further characterised by IR-, Raman-, and solid-state NMR-spectroscopic methods. Moreover, DFT calculations as well as TGA and DSC measurements were performed.

Mo2 B4 O9 -Connecting Borate and Metal-Cluster Chemistry.

We report on the first thoroughly characterized molybdenum borate, which was synthesized in a high-pressure/high-temperature experiment at 12.3 GPa/1300 °C using a Walker-type multianvil apparatus. Mo2 B4 O9 incorporates tetrahedral molybdenum clusters into an anionic borate crystal structure-a structural motif that has never been observed before in the wide field of borate crystal chemistry. The six bonding molecular orbitals of the [Mo4 ] tetrahedron are completely filled with 12 electrons, which are fully delocalized over the four molybdenum atoms. This finding is in agreement with the results of the magnetic measurements, which confirmed the diamagnetic character of Mo2 B4 O9 . The two four-coordinated boron sites can be differentiated in the 11 B MAS-NMR spectrum because of the strongly different degrees of local distortions. Experimentally obtained IR and Raman bands were assigned to vibrational modes based on DFT calculations.

Inorganic SnIP-Type Double Helices in Main-Group Chemistry.

Inspired by the synthesis of the first atomic-scale double-helix semiconductor SnIP, this study deals with the question of whether more atomistic, inorganic double-helix compounds are accessible. With the aid of quantum chemical calculations, we have identified 31 candidates by a homoatomic substitution in MXPn, varying the Group 14 M-element from Si to Pb, the Group 17 X-element from F to I and replacing the pnictide (Pn) phosphorus by arsenic. The double-helical structure of SnIP has been used as the starting model for all candidates and the electronic structure and vibrational spectra were determined within the framework of density functional theory (DFT). Varying the outer MX or the inner Pn helix led to the conclusion that iodide- and bromide-containing MXPn compounds show similar structures to SnIP. Here, the calculations indicate interesting effects for electronic band-gap tuning. For the highly polarized fluorides, a segregation of the helices to more complex MX substructures is predicted.

Synthesis and Characterization of the High-Pressure Nickel Borate γ-NiB4O7.

γ-NiB4O7 was synthesized in a high-pressure/high-temperature experiment at 5 GPa and 900 °C. The single-crystal structure analysis yielded the following results: space group P6522 (No. 179), a = 425.6(2), c = 3490.5(2) pm, V = 0.5475(2) nm3, Z = 6, and Flack parameter x = -0.010(5). Second harmonic generation measurements confirmed the acentric crystal structure. Furthermore, γ-NiB4O7 was characterized via vibrational as well as single-crystal electronic absorption spectroscopy, magnetic measurements, high-temperature X-ray diffraction, differential scanning calorimetry, and thermogravimetry. Density functional theory-based calculations were performed to facilitate band assignments to vibrational modes and to evaluate the elastic properties and phase stability of γ-NiB4O7.

Inorganic Double Helices in Semiconducting SnIP.

SnIP is the first atomic-scale double helical semiconductor featuring a 1.86 eV bandgap, high structural and mechanical flexibility, and reasonable thermal stability up to 600 K. It is accessible on a gram scale and consists of a racemic mixture of right- and left-handed double helices composed by [SnI] and [P] helices. SnIP nanorods <20 nm in diameter can be accessed mechanically and chemically within minutes.

Room-Temperature Synthesis of Thiostannates from {[Ni(tren)]2[Sn2S6]}n.

The compound {[Ni(tren)]2[Sn2S6]}n (1) (tren = tris(2-aminoethyl)amine, C6H18N4) was successfully applied as source for the room-temperature synthesis of the new thiostannates [Ni(tren)(ma)(H2O)]2[Sn2S6]·4H2O (2) (ma = methylamine, CH5N) and [Ni(tren)(1,2-dap)]2[Sn2S6]·2H2O (3) (1,2-dap = 1,2-diaminopropane, C3H10N2). The Ni-S bonds in the Ni2S2N8 bioctahedron in the structure of 1 are analyzed with density functional theory calculations demonstrating significantly differing Ni-S bond strengths. Because of this asymmetry they are easily broken in the presence of an excess of ma or 1,2-dap immediately followed by Ni-N bond formation to N donor atoms of the amine ligands thus generating [Ni(tren)(amine)](2+) complexes. The chemical reactions are fast, and compounds 2 and 3 are formed within 1 h. The synthesis concept presented here opens hitherto unknown possibilities for preparation of new thiostannates.

Conversion Reactions of Solids: From a Surprising Three-Step Mechanism towards Directed Product Formation.

Directed conversion reactions from binary to multinary compounds are discovered from the reaction of Bi2 S3 and Bi2 Se3 with NiCl2 ⋅6 H2 O in polyol media under basic conditions. Control of the synthesis conditions allows the preparation of NiBiSe and superconducting Ni3 Bi2 S2 and Ni3 Bi2 Se2 . The formation of Ni3 Bi2 S2 from Bi2 S3 is found from an unexpected three-step reaction path with Bi and NiBi as intermediates. In the more complex Ni/Bi/Se system, the mechanism found can be used to selectively direct the reaction between the competing ternaries and to suppress side-product formation. Contrary to solid-state reactions (500-900 °C) control of product formation is reached at reaction temperatures and times between 166-300 °C and 0.5-10 h, respectively. The formation of different phases is discussed from results of DFT calculations.

Na2TeS3, Na2TeSe3-mP24, and Na2TeSe3-mC48: Crystal Structures and Optical and Electrical Properties of Sodium Chalcogenidotellurates(IV).

Pure samples of Na2TeS3 and Na2TeSe3 were synthesized by the reactions of stoichiometric amounts of the elements Na, Te, and Q (Q = S, Se) in the ratio 2:1:3. Both compounds are highly air- and moisture-sensitive. The crystal structures were determined by single-crystal X-ray diffraction. Yellow Na2TeS3 crystallizes in the space group P21/c. Na2TeSe3 exists in a low-temperature modification (Na2TeSe3-mP24, space group P21/c) and a high-temperature modification (Na2TeSe3-mC48, space group C2/c); both modifications are red. Density functional theory calculations confirmed the coexistence of both modifications of Na2TeSe3 because they are very close in energy (ΔE = 0.18 kJ mol(-1)). To the contrary, hypothetic Na2TeS3-mC48 is significantly less favored (ΔE = 1.8 kJ mol(-1)) than the primitive modification. Na2TeS3 and Na2TeSe3-mP24 are isotypic to Li2TeS3, whereas Na2TeSe3-mC48 crystallizes in its own structure type, which was first described by Eisenmann and Zagler. The title compounds have two common structure motifs. Trigonal TeQ3 pyramids form layers, and the Na atoms are surrounded by a distorted octahedral environment of chalcogen atoms. Raman spectra are dominated by the vibration modes of the TeQ3 units. The activation energies of the total conductivity of the title compounds range between 0.68 eV (Na2TeS3) and 1.1 eV (Na2TeSe3). Direct principal band gaps of 1.20 and 1.72 eV were calculated for Na2TeSe3 and Na2TeS3, respectively. The optical band gaps are in the range from 1.38 eV for Li2TeSe3 to 2.35 eV for Na2TeS3.

One-Dimensional [P15](-) Tubes in Layered Semiconducting AgP15.

AgP15 was synthesized from the elements via a short-way transport reaction following the mineralizer concept. The needle-shaped crystals were characterized by single-crystal and powder X-ray diffraction. It crystallizes triclinically in space group P1̅ with cell parameters of a = 6.937(1) Å, b = 9.000(1) Å, c = 11.103(2) Å, α = 99.95(1)°, ß = 99.61(1)°, and γ = 105.980(9)°. AgP15 exhibits a tubular phosphorus substructure related but neither isotypic nor isostructural to the alkaline phosphides MP15 (M = Li-Rb). The thermal properties, electronic structure, and experimental band gap of this new semiconductor have been determined. Finally, Raman spectra of AgP15 and selected alkaline-metal polyphosphides MP15 have been measured and interpreted. AgP15 represents the first transition-metal representative of this class of materials.

Tuneable anisotropy and magnetism in Sn2Co3S2-xSex - probed by (119)Sn Mößbauer spectroscopy and DFT studies.

The half metal (HFM) Sn2Co3S2 shows a fascinating S = 1/2 magnetism. Anisotropic coupling of spins in and between Co Kagomé layers by Sn sites is now studied from the substitution effects of S by Se by systematic and local experimental and first principles data. Trends in crystal structure changes (c/a ratio) as retrieved from XRD data on the solid solution Sn2Co3S2-xSex are complemented by DFT modelling on Sn2Co3SeS and hitherto unknown Sn2Co3Se2. The relationship of crystal structure effects with changes in Curie temperatures and magnetic hysteresis is shown from susceptibility measurements. An insight into the role of the Sn sites in magnetism and bonding is gained from (119)Sn Mössbauer spectroscopic measurements. Isomer shifts, quadrupole splitting, and magnetic hyperfine fields are interpreted by DFT calculations on chemical bonding, electric field gradients (EFG), Fermi contact, and spin polarization.

Two Pseudopolymorphic Star-Shaped Tetranuclear Co(3+) Compounds with Disulfide Anions Exhibiting Two Different Connection Modes and Promising Photocatalytic Properties.

The compound [Co4(C6H14N2)4(µ4-S2)2(µ2-S2)4] (I) and the pseudo-polymorph [Co4(C6H14N2)4(µ4-S2)2(µ2-S2)4]⋅4 H2O (II) were obtained under solvothermal conditions (C6H14N2=trans-1,2-diaminocyclohexane). The structures feature S2(2-) ions exhibiting two different coordination modes. Terminal S2(2-) entities join two Co(3+) centres in a µ2 fashion, whereas the central S2(2-) groups connect four Co(3+) cations in a µ4-coordination mode. Compound II can be transformed into compound I by heat and storage over P2O5 and storing compound I in humid air yields in the formation of compound II. The intermolecular interactions investigated through Hirshfeld surface analysis reveal that besides S⋅⋅⋅H bonding close contacts are associated with relatively weak H⋅⋅⋅H interactions. A detailed DFT analysis of the bonding situation explains the long S-S bonds in the µ4-bridging S2(2-) units and the short bonds for the S2(2-) moieties in the µ2-connecting mode. Photocatalytic hydrogen evolution experiments demonstrate the potential of compound II as catalyst.

Reaction of Ni(2+) and SnS as a Way to Form Ni@SnS and Sn2Ni3S2 Nanocrystals: Control of Product Formation and Shape.

Reductive diffusion of Ni(2+) into SnS particles was shown to selectively form Sn2Ni3S2, hybrid, or even core-shell Ni@SnS, Ni1.523Sn, and Ni3S2, by tuning the reaction conditions at low temperatures. The mechanism of Ni(2+) reduction and diffusion into SnS was observed in ethylene glycol, which served both as solvent and reducing agent. Tuning of reaction temperature and duration, morphology of the template SnS, and the application of ethylenediamine as supporting chelating agent, influence the formation of the final products. Their formation was controlled by carefully adjusting redox and equilibrium reactions. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy analysis (EDX).

Black Arsenic-Phosphorus: Layered Anisotropic Infrared Semiconductors with Highly Tunable Compositions and Properties.

New layered anisotropic infrared semiconductors, black arsenic-phosphorus (b-AsP), with highly tunable chemical compositions and electronic and optical properties are introduced. Transport and infrared absorption studies demonstrate the semiconducting nature of b-AsP with tunable bandgaps, ranging from 0.3 to 0.15 eV. These bandgaps fall into the long-wavelength infrared regime and cannot be readily reached by other layered materials.

Synthesis, structural characterization, and physical properties of Cs2Ga2S5, and redetermination of the crystal structure of Cs2S6.

The reaction of CsN3 with GaS and S at elevated temperatures results in Cs2Ga2S5. Its crystal structure was determined from single-crystal X-ray diffraction data. The colorless solid crystallizes in space group C2/c (no. 15) with V = 1073.3(4) Å(3) and Z = 4. Cs2Ga2S5 is the first compound that features one-dimensional chains ∞(1)([Ga2S3(S2)(2-)] of edge- and corner-sharing GaS4 tetrahedra. The vibrational band of the S2(2-) units at 493 cm(-1) was revealed by Raman spectroscopy. Cs2Ga2S5 has a wide bandgap of about 3.26 eV. The thermal decomposition of CsN3 yields elemental Cs, which reacts with sulfur to provide Cs2S6 as an intermediate product. The crystal structure of Cs2S6 was redetermined from selected single crystals. The red compound crystallizes in space group P1 with V = 488.99(8) Å(3) and Z = 2. Cs2S6 consists of S6(2-) polysulfide chains and two Cs positions with coordination numbers of 10 and 11, respectively. Results of DFT calculations on Cs2Ga2S5 are in good agreement with the experimental crystal structure and Raman data. The analysis of the chemical bonding behavior revealed completely ionic bonds for Cs, whereas Ga-S and S-S form polarized and fully covalent bonds, respectively. HOMO and LUMO are centered at the S2 units.

The extended stability range of phosphorus allotropes.

Phosphorus displays fascinating structural diversity and the discovery of new modifications continues to attract attention. In this work, a complete stability range of known and novel crystalline allotropes of phosphorus is described for the first time. This includes recently discovered tubular modifications and the prediction of not-yet-known crystal structures of [P12] nanorods and not-yet-isolated [P14] nanorods. Despite significant structural differences, all P allotropes consist of covalent substructures, which are held together by van der Waals interactions. Their correct reproduction by ab initio calculations is a core issue of current research. While some predictions with the established DFT functionals GGA and LDA differ significantly from experimental data in the description of the P allotropes, consistently excellent agreement with the GGA-D2 approach is used to predict the solid structures of the P nanorods.

Cd4Cu7As, the first representative of a fully ordered, orthorhombically distorted MgCu2 Laves phase.

The ternary Laves phase Cd(4)Cu(7)As is the first intermetallic compound in the system Cu-Cd-As and a representative of a new substitution variant for Laves phases. It crystallizes orthorhombically in the space group Pnnm (No. 58) with lattice parameters a = 9.8833(7) Å; b = 7.1251(3) Å; c = 5.0895(4) Å. All sites are fully occupied within the standard deviations. The structure can be described as typical Laves phase, where Cu and As are forming vertex-linked tetrahedra and Cd adopts the structure motive of a distorted diamond network. Cd(4)Cu(7)As was prepared from stoichiometric mixtures of the elements in a solid state reaction at 1000 °C. Magnetic measurements are showing a Pauli paramagnetic behavior. During our systematical investigations within the ternary phase triangle Cd-Cu-As the cubic C15-type Laves phase Cd(4)Cu(6.9(1))As(1.1(1)) was structurally characterized. It crystallizes cubic in the space group Fd3m with lattice parameter a = 7.0779(8) Å. Typically for quasi-binary Laves phases Cu and As are both occupying the 16c site. Chemical bonding, charge transfer and atomic properties of Cd(4)Cu(7)As were analyzed by band structure, ELF, and AIM calculations. On the basis of the general formula for Laves phases AB(2), Cd is slightly positively charged forming the A substructure, whereas Cu and As represent the negatively charged B substructure in both cases. The crystal structure distortion is thus related to local effects caused by Arsenic that exhibits a larger atomic volume (18 Å(3) compared to 13 Å(3) for Cu) and higher ionicity in bonding.