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Glycerol is a renewable chemical that has become widely available and inexpensive due to the increased production of biodiesel. Noble metal materials have shown to be effective catalysts for the production of hydrogen and value-added products through the electrooxidation of glycerol. In this work we develop three platinum systems with distinct pore mesostructures, e.g., hierarchical pores (HP), cubic pores (CP) and linear pores (LP); all with high electrochemically active surface area (ECSA). The ECSA-normalized GEOR catalytic activity of the systems follows HPC > LPC > CPC > commercial Pt/C. Regarding the oxidation products, we observe glyceric acid as the main three-carbon product (3C), with oxalic acids as the main two-carbon oxidation product. DFT-based theoretical calculations support the glyceraldehyde route going through tartronic acid towards oxalic acid and also help understanding why the dihydroxyacetone (DHA) route is active despite the absence of DHA amongst the observed oxidation products.

Lignin is an aromatic polymer that constitutes up to 30 wt% of woody biomass and is considered the largest source of renewable aromatics. Valorization of the lignin stream is pivotal for making biorefining sustainable. Monomeric units in lignin are bound via C–O and C–C bonds. The majority of existing methods for the production of valuable compounds from lignin are based on the depolymerization of lignin via cleavage of relatively labile C–O bonds within lignin structure, which leads to yields of only 36–40 wt%. The remaining fraction (60 wt%) is a complex mixture of high-molecular-weight lignin, generally left unvalorized. Here we present a method to produce additional valuable monomers from the high-molecular-weight lignin fraction through oxidative C–C bond cleavage. This oxidation reaction proceeds with a high selectivity to give 2,6-dimethoxybenzoquinone (DMBQ) from high-molecular-weight lignin in 18 wt% yield, thus increasing the yield of monomers by 32%. This is an important step to make biorefining competitive with petroleum-based refineries. The valorization of lignin is generally implemented through the cleavage of labile C–O bonds to produce aromatic monomers in up to 40 wt% yield. The remaining material consists of lignin dimers and oligomers connected by C–C bonds, but now a method has been developed for the oxidative cleavage of these C–C bonds using oxoammonium salts, to produce benzoquinones.

Uranium carbide (UC) is a candidate fuel material for future Generation IV nuclear reactors. As part of a general safety assessment, it is important to understand how fuel materials behave in aqueous systems in the event of accidents or upon complete barrier failure in a geological repository for spent nuclear fuel. As irradiated nuclear fuel is radioactive, it is important to consider radiolysis of water as a process where strongly oxidizing species can be produced. These species may display high reactivity toward the fuel itself and thereby influence its integrity. The most important radiolytic oxidant under repository conditions has been shown to be H2O2. In this work, we have studied the dissolution of uranium upon exposure of UC powder to aqueous solutions containing HCO3- and H2O2, separately and in combination. The experiments show that UC dissolves quite readily in aqueous solution containing 10 mM HCO3- and that the presence of H2O2 increases the dissolution further. UC also dissolves in pure water after the addition of H2O2, but more slowly than in solutions containing both HCO3- and H2O2. The experimental results are discussed in view of possible mechanisms.

Aurivillius oxides have been a research focus due to their ferroelectric properties, but by replacing oxide ions by fluoride, divalent magnetic cations can be introduced, giving Bi

Transparent single crystals of two new iodates K3Sc(IO3)6 and KSc(IO3)3Cl have been synthesized hydrothermally. Single-crystal X-ray diffraction was used to determine their crystal structures. Both compounds crystallize in non-centrosymmetric space groups. The compound K3Sc(IO3)6 crystallizes in the orthorhombic space group Fdd2. The crystal structure is made up of [ScO6] octahedra, [IO3] trigonal pyramids, and [KO8] distorted cubes. The compound KSc(IO3)3Cl crystallizes in the trigonal space group R3. The building blocks are [ScO6] octahedra, [KO12] polyhedra, and [IO3] trigonal pyramids. The Cl- ions act as counter ions and reside in tunnels in the crystal structure. The second harmonic generation (SHG) measurements at room temperature, using 1064 nm radiation, on polycrystalline samples show that the SHG intensities of K3Sc(IO3)6 and KSc(IO3)3Cl are around 2.8 and 2.5 times that of KH2PO4 (KDP), respectively. In addition, K3Sc(IO3)6 and KSc(IO3)3Cl are phase-matchable at the fundamental wavelength of 1064 nm. The large anharmonicity in the optical response of both compounds is further supported by an anomalous temperature dependence of optical phonon frequencies as well as their enlarged intensities in Raman scattering. The latter corresponds to a very large electronic polarizability.

In this study, the effect of SiC particle size on the sintering behavior of SiC-Si nano composites fabricated by spark plasma sintering (SPS) technique was investigated and a model was proposed, accordingly. To this purpose, SiC powders with three different particle sizes of 25 µm, 80 nm and 45 nm were chosen. It was expected that hardness of the composites increase with decreasing the SiC particle size; however, the outcomes were interesting and unpredictable. The composite with 80 nm SiC particles indicated the highest hardness. Hardness of the specimen with 25 µm SiC was low because of the large particle size of its reinforcement. While 80 and 45 nm SiC particles are considered as nano particles, the composite with 45 nm SiC particles showed lower hardness due to the growth of SiC powders during sintering according to a proposed model. Two reasons for the growth of 45 nm SiC particles were defined: (i) the fineness of the SiC particles prevented the Si particles to act as a binder between them thus, they agglomerated; (ii) SiC powders were oxidized during mixing procedure and a layer of SiO2 was formed on their surfaces. During sintering procedure, the reaction between SiC and SiO2 was happened and as a result SiO was formed. It caused vapor transportation during sintering leading to necking between particles and in turn, grain growth.

Glycerol electrolysis affords a green and energetically favorable route for the production of value-added chemicals at the anode and H

Uranium carbide (UC) is a candidate fuel material for future Generation IV nuclear reactors. As part of a general safety assessment, it is important to understand how fuel materials behave in aqueous systems in the event of accidents or upon complete barrier failure in a geological repository for spent nuclear fuel. As irradiated nuclear fuel is radioactive, it is important to consider radiolysis of water as a process where strongly oxidizing species can be produced. These species may display high reactivity toward the fuel itself and thereby influence its integrity. The most important radiolytic oxidant under repository conditions has been shown to be H

Investigation of new high-efficiency catalysts for the oxygen evolution reaction (OER) is important for propelling the practical applications of water splitting. Here we report the Aurivillius comp ...

SiC–Si composites are widely used either as a bulk material or as a matrix for fibre reinforced ceramics. In the current research, nanocomposites of SiC–Si with different volume fractions of Si wer...

Glycerol is a byproduct of biodiesel production and, as such, it is of limited economic value. By means of electrooxidation, glycerol can be used as a feedstock for scalable hydrogen production, in addition to conversion to value-added products. The development of novel and efficient catalytic electrode materials for the anodic side of the reaction is a key towards a hydrogen-based energy economy. In the present study, a computational screening protocol combining DFT, scaling relations, and microkinetic modeling allows for a rational selection of novel catalysts that can deliver efficient glycerol electrooxidation, low cost of production, and environmental sustainability. Activity and chemical selectivity towards hydrogen production on pure metal catalysts is discussed in terms of volcano-shaped plots. We find that the selectivity in the glycerol oxidation reaction is influenced by a different energy landscape when in the presence of water and best classified by a comparison of O-H and C-H bond-breaking barriers. In addition, we screened 3570 bi-metallic catalysts in the AB (L1(0)) and A(3)B (L1(2)) ordered structures for activity, stability, price, and toxicity. By filtering based on the criteria for toxicity, resistance to oxidation, miscibility, and price, we have identified 5 L1(0) structured catalysts (AgPd, AuPd, PtSb, CuPt, and AgPt) and 20 L1(2) catalysts (Ga3Ta, In3Ta, Ir3W, Ir3Mo, Cu3Pt, Ir3Ta, Ir3Re, Pd3Bi, Pd3Cu, Pd3W, Pd3Co, Pd3Sn, Pd3Mo, Pd3Ag, Pd3Ga, Pd3Ta, Au3Ru, Pd3In, Au3Ir, and Pd3Au) that are all predicted to show high activity. We also identify an additional 37 L1(0) and 92 L1(2) structured electrocatalysts with an anticipated medium-high activity. (C) 2021 The Author(s). Published by Elsevier Ltd.

Glycerol electrolysis affords a green and energetically favorable route for the production of value-added chemicals at the anode and H2 production in parallel at the cathode. Here, we report a novel and facile method for trapping Pt nanoparticles at oxygen vacancies of molybdenum oxide (MoOx) nanosheets, yielding a high-performance MoOx/Pt composite electrocatalyst for both the glycerol oxidation reaction (GOR) and the hydrogen evolution reaction (HER) in alkaline electrolytes. Combined electrochemical experiments and theoretical calculations revealed the important role of MoOx nanosheets for the adsorption of glycerol molecules in GOR and the dissociation of water molecules in HER, as well as the strong electronic interaction with Pt. With MoOx/Pt electrodes serving as both cathode and anode, we achieve two-electrode glycerol electrolysis at a cell voltage of 0.70 V to reach a current density of 10 mA cm− 2, which is 0.90 V less than that required for water electrolysis.

Lignin is an aromatic polymer that constitutes up to 30 wt% of woody biomass and is considered the largest source of renewable aromatics. Valorization of the lignin stream is pivotal for making biorefining sustainable. Monomeric units in lignin are bound via C-O and C-C bonds. The majority of existing methods for the production of valuable compounds from lignin are based on the depolymerization of lignin via cleavage of relatively labile C-O bonds within lignin structure, which leads to yields of only 36-40 wt%. The remaining fraction (60 wt%) is a complex mixture of high-molecular-weight lignin, generally left unvalorized. Here we present a method to produce additional valuable monomers from the high-molecular-weight lignin fraction through oxidative C-C bond cleavage. This oxidation reaction proceeds with a high selectivity to give 2,6-dimethoxybenzoquinone (DMBQ) from high-molecular-weight lignin in 18 wt% yield, thus increasing the yield of monomers by 32%. This is an important step to make biorefining competitive with petroleum-based refineries.

Transparent single crystals of two new iodates K3Sc(IO3)6 and KSc(IO3)3Cl have been synthesized hydrothermally. Single-crystal X-ray diffraction was used to determine their crystal structures. Both compounds crystallize in non-centrosymmetric space groups. The compound K3Sc(IO3)6 crystallizes in the orthorhombic space group Fdd2. The crystal structure is made up of [ScO6] octahedra, [IO3] trigonal pyramids, and [KO8] distorted cubes. The compound KSc(IO3)3Cl crystallizes in the trigonal space group R3. The building blocks are [ScO6] octahedra, [KO12] polyhedra, and [IO3] trigonal pyramids. The Cl– ions act as counter ions and reside in tunnels in the crystal structure. The second harmonic generation (SHG) measurements at room temperature, using 1064 nm radiation, on polycrystalline samples show that the SHG intensities of K3Sc(IO3)6 and KSc(IO3)3Cl are around 2.8 and 2.5 times that of KH2PO4 (KDP), respectively. In addition, K3Sc(IO3)6 and KSc(IO3)3Cl are phase-matchable at the fundamental wavelength of 1064 nm. The large anharmonicity in the optical response of both compounds is further supported by an anomalous temperature dependence of optical phonon frequencies as well as their enlarged intensities in Raman scattering. The latter corresponds to a very large electronic polarizability.

The new CoBi2O2F4 compound was synthesized by a hydrothermal method at 230 °C. Single-crystal X-ray diffraction data were used to determine the crystal structure. The compound is layered and belong...

A synthesis procedure for fabrication of hollow TiO2 spheres of mixed anatase/rutile composition loaded with noble metal nanoparticles (Au, Pt, Pd) is proposed. The materials demonstrated to be functioning photocatalysts for water oxidation. In particular nanoparticles loaded with Pd and Pt showed good catalytic activity in comparison to commercial TiO2 P25.

Single crystals of the new compound Cu2(SeO3)F2 were successfully synthesized via a hydrothermal method, and the crystal structure was determined from single-crystal X-ray diffraction data. The compound crystallizes in the orthorhombic space group Pnma with the unit cell parameters a = 7.066(4) A, b = 9.590(4) A, and c = 5.563(3) A. Cu2(SeO3)F2 is isostructural with the previously described compounds Co2TeO3F2 and CoSeO3F2. The crystal structure comprises a framework of corner- and edge-sharing distorted [CuO3F3] octahedra, within which [SeO3] trigonal pyramids are present in voids and are connected to [CuO3F3] octahedra by corner sharing. The presence of a single local environment in both the 19F and 77Se solid-state MAS NMR spectra supports the hypothesis that O and F do not mix at the same crystallographic positions. Also the specific phonon modes observed with Raman scattering support the coordination around the cations. At high temperatures the magnetic susceptibility follows the Curie–Weiss law with...

Zn 3 Sb 4 O 6 F 6 has been synthesized hydrothermally at 230 °C. The crystal structure was determined from single crystal X-ray diffraction data. It crystallizes in the cubic non-centrosymmetric space group I -43 m with the unit cell parameter a = 8.1291(4) A and is isostructural with M 3 Sb 4 O 6 F 6 (M = Co, Ni). The new compound is the first oxofluoride containing Zn 2+ and a p-element cation with a stereochemically active lone pair. The crystal structure is made up by [ZnO 2 F 4 ] octahedra forming a network via corner sharing at F-atoms and [SbO 3 ] trigonal pyramids that form [Sb 4 O 6 ] cages that connect via the O-atoms to the Zn-atoms. Powder second-harmonic generation (SHG) measurements using 1064 nm radiation on Zn 3 Sb 4 O 6 F 6 indicate an SHG intensity of approximately 40 × α-SiO 2 .

An experimental setup and routine is presented for evaluating potential catalysts for water splitting by means of measuring Faradaic efficiency in real time by coupled potentiometry and mass spectr ...

The new oxofluoride compound FeSbO2F2 was synthesized by hydrothermal techniques at 230 °C. Its crystal structure was determined from single-crystal X-ray diffraction data. The compound crystallizes in the monoclinic space group C2/c with one crystallographic site for Fe3+ and Sb3+, respectively. The crystal structure is made of [FeO2F4] octahedra and seesaw [SbO4] building blocks. These are connected to form [FeO2F2]n layers and [SbO2]n chains that bond together via the oxygen atoms to form the three-dimensional framework structure. Magnetic susceptibility and heat capacity measurements indicate long-range anti-ferromagnetic ordering below a Neel temperature of ∼175 K. Two-dimensional anti-ferromagnetic short-range order in the square planar net of the Fe3+ cations extends to temperatures far above the Neel temperature.

Reducing package-related cost is essential for various companies and institutions. Different packages are usually designed separately for each and every product, which results in less cost-effective packaging systems. In this study, a data mining model with three clustering algorithms was developed to modularize a packaging system by reducing the variety of packaging sizes. The three algorithms were k-means clustering, agglomerative hierarchical clustering and self-organizing feature map. The package models with similar shapes and sizes were clustered automatically and replaced by one package model with a size that suited them all. The study also analysed the financial effects including the purchasing and inventory costs of the package material and the transportation cost of the packaged products. The case study was carried out at Ericsson to select the best clustering algorithm of the three and to test the effectiveness and applicability of the proposed model. The results show that the packaging system modularized by the agglomerative hierarchical clustering algorithm is more cost-effective in this case compared with the ones modularized by the other two clustering algorithms and with the one without modularization. Copyright © 2017 John Wiley & Sons, Ltd.

The structural and electrochemical properties of a quaternary layered compound with elemental composition Mn2Sb3O6Cl have been investigated upon reaction with lithium in Li half cells. Operando XRD was used to investigate the potential impact of this particular layered structure on the lithiation process. Although the results suggest that the material is primarily reacted through a conventional conversion mechanism, they also provide some hints that the space between the slabs may act as preferential entry points for lithium ions but not for the larger sodium ions. Cyclic voltammetry, galvanostatic cycling, HRTEM, SAED, and EELS analyses were performed to unravel the details of the reaction mechanism with the lithium ions. It is found that two pairs of reactions are mainly responsible for the reversible electrochemical cycling of this compound, namely, the alloying of Li–Sb and the conversion of MnxOy to metallic Mn0 with concomitant formation of Li2O upon lithium uptake. A moderate cycling stability is a...

Lanthanum doped strontium titanate is a potential n-type thermoelectric material at moderate and high temperatures. (La0.12Sr0.88)0.95TiO3 ceramics were prepared by two different routes, conventional sintering at 1500 °C and spark plasma sintering at temperatures between 925 and 1200 °C. Samples with grain size between 40 nm and 1.4 μm were prepared and characterized with respect to their thermoelectric transport properties at temperatures between 100 and 900 °C under reducing conditions (H2/H2O-buffer mixtures). The thermal conductivity was significantly reduced with decreasing grain size reaching a value of 1.3 W m−1. K−1 at 600 °C for grain size of 40 nm and porosity of 19%. Electrical conductivity increased with increasing grain size showing a maximum of 500 S cm−1 at 200 °C for a grain size of 1.4 μm. The highest figure-of-merit (zT) was measured for samples with 1.4 μm average grain size reaching 0.2 at 500 °C.

Catalysts based on earth-abundant non-noble metals are interesting candidates for alkaline water electrolysis in sustainable hydrogen economies. However, such catalysts often suffer from high overp ...

The new quaternary layered oxide CoMo2Sb2O10 was synthesized by hydrothermal synthesis techniques, and its structure was determined from single-crystal X-ray diffraction data. CoMo2Sb2O10 crystallizes in the monoclinic space group C2/c with one Sb3+, Mo6+, and Co2+ atom site per unit cell, respectively. The crystal structure contains building units consisting of [Co2O8]n, [Mo2O8]n, and [SbO2]n chains. These are connected through corner sharing to form charge-neutral [CoMo2Sb2O10]n layers. Thermal decomposition of CoMo2Sb2O10 starts at 550 °C. The magnetic susceptibility follows a Curie–Weiss law above 50 K with a Curie constant of C = 3.46 emu·K·mol–1 corresponding to an effective moment of μeff = 5.26 μB per cobalt atom and a Curie–Weiss temperature θ = −13.2 K. Short-range anti-ferromagnetic ordering dominates below 5 K. Magnetic susceptibility and heat capacity data can be successfully modeled by the predictions from an Ising linear chain with an intrachain spin exchange of ca. −7.8 K.

A group of oxohalides, where Ni3Sb4O6F6 is one example, has been investigated with respect to its electrochemical reactions toward Li+/Li. In situ and ex situ XRD measurements reveal that the original structure collapses and the material becomes amorphous upon insertion of Li at low potentials versus Li+/Li. With continued cycling, a nanocrystalline phase of NiSb, which reacts reversibly with Li, appears and steadily grows more stable. Electrochemical experiments (i.e., chronopotentiometry and cyclic voltammetry) show that multiple reactions of both conversion- and alloying-type are active in the system. High storage capacities are achieved initially but with rapid fading as a consequence of a limited reversibility of the Ni2+/Ni redox process, as shown by X-ray absorption spectroscopy of the first discharge/charge cycle. Stable cycling can be achieved by optimizing the cutoff potentials (i.e., excluding poorly reversible reactions at high and low voltages, respectively), yielding long-term cycling with a practical gravimetric capacity of similar to 200 mAh g(-1).

Low temperature thermoelectric (TE) materials are in demand for more efficient cooling and power generation applications. Iron antimonide (FeSb2) draws great attention over the past few years because of its enhanced power factor values. Polycrystalline bulk FeSb2 nanopowder was prepared via a low-temperature molten salts approach followed by subsequent thermal treatment in synthetic air and hydrogen gas for calcination and reduction reactions, respectively. Structural analysis confirms the desired final phase with submicrometer grain size and high compaction density after consolidation using spark plasma sintering (SPS). TE transport properties revealed that the material is n-type below 150 K and p-type above this temperature; this suggests antimony vacancies in FeSb2. The electrical conductivity increased significantly, and the highest conductivity achieved was 6000 S/cm at 100 K. The maximum figure-of-merit, ZT, of 0.04 is achieved at 500 K, which is about 6 times higher than the earlier reported state-of-the art ZT value for the same material.

The single crystals of the new isostructural compounds Sb3O4F and Y0.5Sb2.5O4F and the two previously known compounds M-SbOF and α-Sb3O2F5 were successfully grown by a hydrothermal technique at 230 °C. The new compound Sb3O4F crystallizes in the monoclinic space group P21/c; a = 5.6107(5) Å, b = 4.6847(5) Å, c = 20.2256(18) Å, β = 94.145(8)°, z = 4. The replacing part of Sb with Y means a slight increase in the unit cell dimensions. The compounds M-SbOF and α-Sb3O2F5 have not been grown as single crystals before and it can be concluded that hydrothermal synthesis has proved to be a suitable technique for growing single crystals of antimony oxofluorides because of the relatively low solubility of such compounds compared to other antimony oxohalides that most often have been synthesised at high temperatures by solid state reactions or gas-solid reactions.

The recently described solid solution (Co,Ni,Mn)3Sb4O6F6has proved stable and efficient as a catalyst for electrocatalytic water oxidation. The end component Co3Sb4O6F6was found to be most efficient, maintaining a current density ofj= 10 mA cm−2at an overpotential of 443 mV with good capability. At this current density, O2and H2were produced in the ratio 1 : 2 without loss of faradaic current against a Pt-cathode. A morphological change in the crystallite surface was observed after 0.5 h, however, even after 64.5 h, the overall shape and size of the small crystallites were unaffected and the electrolyte contained only 0.02 at% Co. It was also possible to conclude fromin situEXAFS measurements that the coordination around Co did not change. The oxofluorides express both hydrophilic and hydrophobic surface sites, incorporate a flexible metalloid element and offer the possibility of a mechanism that differs from other inorganic catalytic pathways previously described.

The application of the recently discovered oxofluoride solid solution (Cox Ni1-x )3 Sb4 O6 F6 as a catalyst for water oxidation is demonstrated. The phase exhibits a cubic arrangement of the active metal that forms oxo bridges to the metalloid with possible catalytic participation. The Co3 Sb4 O6 F6 compound proved to be capable of catalyzing 2H2 O→O2 +4H(+) +4e(-) at 0.33 V electrochemical and ≤0.39 V chemical overpotential with a TOF of 4.4⋅10(-3) , whereas Ni3 Sb4 O6 F6 needs a higher overpotential. Relatively large crystal cubes (0.3-0.5 mm) are easily synthesized and readily handled as they demonstrate both chemical resistance to wear after repeated in situ tests under experimental conditions, and have a mechanical hardness of 270 V0.1 using Vickers indentation. The combined properties of this compound offer a potential technical advantage for incorporation to a catalytic interface in future sustainable fuel production.

The new compound Co 2 Te 3 (PO 4 )O 6 Cl was synthesized by chemical reactions in a sealed and evacuated silica tube. The crystal structure was solved from single crystal diffraction data and is made up by charge neutral layers. Within the layers two types of chains are made up by edge sharing [CoO 6 ] and [CoO 5 Cl] polyhedra respectively. The chains are separated by tellurium oxide and phosphate building blocks. There are only weak Van der Waals interactions in between the layers and severe diffuse scattering is observed due to faulted stacking of the layers. Structure solutions in a P -1 triclinic cell and a larger monoclinic cell in P 2 1 / c are discussed and compared to a computer generated model. The reasons for the stacking faults may be due to that there are two positions available for each layer that results in similar connectivity to the next layer in addition to the relatively wide channels in between the layers that reduce the Van der Waals interactions in between them.

The new oxofluoride compound FeSbO

Phase identification and structure characterization are important in synthetic and materials science. It is difficult to characterize the individual phases from multiphase crystalline powder samples, especially if some of the phases are unknown. This problem can be solved by combining rotation electron diffraction (RED) and powder X-ray diffraction (PXRD). Four phases were identified on the same transmission electron microscopy grid from a multiphase sample in the Ni–Se–O–Cl system, and their structures were solved from the RED data. Phase 1 (NiSeO3) was found in the Inorganic Crystal Structure Database using the information from RED. Phase 2 (Ni3Se4O10Cl2) is an unknown compound, but it is isostructural to Co3Se4O10Cl2, which was recently solved by single-crystal X-ray diffraction. Phase 3 (Ni5Se6O16Cl4H2) and Phase 4 (Ni5Se4O12Cl2) are new compounds. The fact that there are at least four different compounds in the as-synthesized material explains why the phase identification and structure determination could not be done by PXRD alone. The RED method makes phase identification from such multiphase powder samples much easier than would be the case using powder X-ray diffraction. The RED method also makes structure determination of submicrometre-sized crystals from multiphase samples possible.

The new compounds Mn4(TeO3)(SiO4)X2 (X=Br, Cl) were synthesized by solid state reactions in sealed evacuated silica tubes. The compounds crystallize in the monoclinic space group P21/m with the unit cell parameters a=5.5463(3) A (5.49434(7) A), b=6.4893(4) A (6.44184(9) A), c=12.8709(7) A (12.60451(18) A), β=93.559(5)° (94.1590(12)°) and Z=2 for the respective Br and Cl analogues. Manganese adopts various distorted coordination polyhedra; [MnO6] octahedra, [MnO5] tetragonal pyramids and [MnO2X2] tetrahedra. Other building blocks are [SiO4] tetrahedra and [TeO3] trigonal pyramids. The structure is made up from layers having no net charge that are connected via weak Van der Waal interactions. The layers that are parallel to (1 1 0) consist of two manganese oxide sheets which are separated by [SiO4] tetrahedra. On the outer sides of the sheets are the [MnO2X2] tetrahedra and the [TeO3] trigonal pyramids connected so that the halide ions and the stereochemically active lone pairs on the tellurium atoms protrude from the layers. Magnetic susceptibility measurements reveal a Curie law with a Weiss temperature of θ=−153(3) K for temperatures ≥100 K and indicate antiferromagnetic ordering at TN ~4 K. Possible structural origins of the large frustration parameter of f=38 are discussed.

The structural architecture found in low-dimensional materials can lead to a number of interesting physical properties including anisotropic conductivity, magnetic frustration and non-linear optical properties. There is no standard synthesis concept described thus far to apply when searching for new low-dimensional compounds, and therefore control on the design of the new materials is of great importance.This thesis describes the synthesis, crystal structure and characterization of some new transition metal oxohalide compounds containing p-elements having a stereochemically active lone-pair. First row transition metal cations have been used in combination with SeIV, SbIII and TeIV ions as lone-pair elements and Cl- and Br- as halide ions. The lone-pairs do not participate in covalent bonding and are responsible for an asymmetric one-sided coordination. Lone-pair elements in combination with halide ions have shown to be powerful structural spacers that can confine transition metal building blocks into low-dimensional arrangements. The halide ions and lone-pairs reside in non-bonded crystal volumes where they interact through weak van der Waals forces. The transition metal atoms are most often arranged to form sheets, chains or small clusters; most commonly layered compounds are formed.To further explore the chemical system and to separate the transition metal entities even more the possibility to include tetrahedral building blocks such as phosphate-, silicate-, sulphate- and vanadate building blocks into this class of compounds has been investigated. Tetrahedral building blocks are well known for their ability of segmenting structural arrangements by corner sharing, which often leads to the formation of open framework structures. The inclusion of tetrahedral building blocks led to the discovery of interesting structural features such as complex hydrogen bonding, formation of unusual solid solutions or faulted stacking of layers.Compounds for which phase pure material could be synthesized have been characterized in terms of their magnetic properties. Most compounds were found to have antiferromagnetic spin interactions and indications of magnetic frustration could be observed in some of them.

The synthesis and crystal structure of eight new layered compounds in the (Mn2+, Fe2+)-(Sb3+, Te4+)-O-(Cl, Br) system are presented. Mn5Te4O12Cl2 (1), MnSb4O6Cl2 (2), Mn2Sb3O6Cl (3), Mn9Sb8O16Cl10 (4), Fe3Sb2O4Br4 (5), Fe7Sb10O18X8 [X = Cl (6), Br (7)], and Mn7Sb10O18Br8 (8). All of the compounds are made up of charge neutral layers held together through van der Waals interactions, except for compound 2, which has positively charged layers with halide ions between them that act as counterions. The transition metal atoms are confined in sheets within the layers and are thus well separated from each other along the stacking direction. The synthesis concept is based on utilizing both halide ions and p-elements having a stereochemically active lone pair that both act to open up crystal structures. This combination has proven to be a successful synthetic approach for finding new layered inorganic materials containing transition metals.