Materials with potential for high temperature inorganic pigment applications (e.g. ceramics) have been synthesised using solid state methods and characterised using powder X-ray and neutron diffraction, magic angle spinning NMR, Mossbauer spectroscopy, UVNis spectroscopy and colour measurement techniques. A number of compounds containing tin (H) and niobium (V) have been modified and doped with various constituents to tailor and widen the colour properties of the bright yellow parent phases. The dark yellow (L*(91.28), a*(13.74), b*(54.76)) tin niobium oxide pyrochlores have been re-characterised using neutron diffraction techniques. These materials exhibit both cation and anion disorder caused by a stereoactive lone pair on the tin (H) metal centres. Solid state NMR and Mossbauer studies have shown the presence of tin (IV) on a symmetric site within the primary phase of the pure oxide pyrochlore and methods have been investigated to minimise the tin (H) disproportion method from where the tin (IV) is derived.

Sustainable and renewable energy is an incredibly important area in today’s society and investigation into avenues to improve this wide ranging technology are underway in many different fields. Thermoelectric devices possess the ability for the direct solid-state interconversion of heat and electrical power, which not only allows for sustainable refrigeration but also waste heat recovery. One current restriction on the efficiency of thermoelectric devices is the disparity in thermoelectric performance of p-type and n-type materials. Furthermore, a key physical attribute shared by the majority of high performing thermoelectric materials is low thermal conductivity. Thus in this thesis three separate p-type material systems exhibiting low thermal conductivity will be discussed. The Cu-excessed quaternary chalcogenides, CuM2InTe4 (M = Zn, Cd), and ternary chalcogenide, CuSbS2, were investigated due to their intrinsically low thermal conductivity. Whereas, skutterudites typically have good electrical properties but do not exhibit an intrinsically low thermal conductivity. Nevertheless low thermal conductivity can be achieved by taking advantage of their unique crystal structure by filling large voids with loosely bound atoms that act as phonon scattering centers. Therefore double-filled Fe substituted skutterudites with nominal compositions Yb0.4In0.02Co3FeSb12 and Yb0.8In0.02Co2.5Fe1.5Sb12 were also investigated. The CuM2InTe4 (M = Zn, Cd) and skutterudite specimens were synthesized by direct reactions, whereas the CuSbS2 specimens were synthesized by mechanical alloying. Structural and stoichiometric compositions were analyzed by a combination of X-ray diffraction, Rietveld refinement and energy dispersive spectroscopy. High-temperature transport properties were measured for all specimens and will be discussed in detail. The Cu-excessed quaternary chalcogenides display intrinsically low thermal conductivity that appears to be unaffected by the change in electrical properties that is a result of differing stoichiometries. This may provide a possible route to furthering the enhancement of the thermoelectric properties of these materials. Similarly the CuSbS2 ternary chalcogenides display a very low thermal conductivity due to stereochemically active lone-pair electrons and would potentially allow an optimization of the power factor without a significant increase of the very low thermal conductivity, thus improving the figure of merit. For the case of p-type skutterudites, (Yb, In) double-filled skutterudites have a maximum ZT of 0.6, which is promising in the hunt for improved p-type materials. This fundamental investigation provides insight that can lead to a deeper understanding of all three material systems outlined in this thesis and provides a platform for new research in the quest for materials suitable for thermoelectric applications.

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. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 6: Manuscript. Paper 9: Manuscript. Paper 10: Manuscript.</p>

Recent structural studies evidenced the presence of a recurring well-known interaction between an oxygen atom and an aromatic nucleobase ring in structural motifs of nucleic acids. In particular, this type of interaction is observed between the O4' atom of the (deoxy)ribose moiety and the aromatic nucleobase in Z-DNA molecules and in a variety of structural RNA molecules. In this thesis, we comprehensively examine the hitherto undetected stacking interactions between an oxygen atom of a water (Ow) molecule and the aromatic nucleobase ring, using structural bioinformatics along with quantum mechanics. On the basis of the structural analysis of the high-resolution X-ray structures, we found out that the stacking distance between the Ow atom and the nucleobase plane varies between 3.1 and 4.0 Å. Further, the contact between the Ow-nucleobase plane can be categorized either as a lonepair-π type, where the Ow atom interacts directly with the aromatic surface of the nucleobase, or as an OH-π interaction, where one of the hydrogen atoms of the Ow points towards the nucleobase. Our quantum chemical analysis evidenced that the OH-π interaction is clearly favored in terms of energetics when compared to the lonepair-π, except for the uracil, where the lonepair-π kind of interaction seems to be energetically more stable, as also supported by electrostatic potential map calculations.

<p>Complex transition metals oxyhalides containing a lone pair element, such as tellurium (IV), form an attractive research field because there is a high probability of finding new low-dimensionally arranged compounds and, particularly, a low-dimensionally arranged transition metals substructures, leading to interesting physical properties. Tellurium (IV) can drive the formation of many unusual structures because of its stereochemically active lone pair electrons, E. It commonly takes a coordination of three or four oxygen atoms to form either a TeO3E square pyramid or a TeO3+1E trigonal bipyramid. These lone pairs are very important players involved in lowering the dimensionality of crystal structures. Previous studies in transition metal tellurium (IV) oxohalide quarternary systems revealed a family of compounds, many of which exhibit interesting properties e.g. magnetic frustration. The unique point of this thesis is to employ alkaline earth elements (AE) to augment this ability of lone pair elements to lower the dimensionality of the transition metal arrangements. By this double usage of “chemical scissors” (a lone pair element used in conjunction with alkaline earth elements) we obtained new types of low-dimensionally arranged compounds.</p><p>This thesis is focused on the syntheses and characterization of a series of compounds in the pentanary (five components) system AE-TeIV-TM-O-X (AE=alkaline earth metal, TM=transition metal and X=halogen), in which nine new compounds were found. The crystal structures of each of these compounds were determined by the single crystal X-ray diffraction data.</p>

Complex transition metals oxyhalides containing a lone pair element, such as tellurium (IV), form an attractive research field because there is a high probability of finding new low-dimensionally arranged compounds and, particularly, a low-dimensionally arranged transition metals substructures, leading to interesting physical properties. Tellurium (IV) can drive the formation of many unusual structures because of its stereochemically active lone pair electrons, E. It commonly takes a coordination of three or four oxygen atoms to form either a TeO3E square pyramid or a TeO3+1E trigonal bipyramid. These lone pairs are very important players involved in lowering the dimensionality of crystal structures. Previous studies in transition metal tellurium (IV) oxohalide quarternary systems revealed a family of compounds, many of which exhibit interesting properties e.g. magnetic frustration. The unique point of this thesis is to employ alkaline earth elements (AE) to augment this ability of lone pair elements to lower the dimensionality of the transition metal arrangements. By this double usage of “chemical scissors” (a lone pair element used in conjunction with alkaline earth elements) we obtained new types of low-dimensionally arranged compounds. This thesis is focused on the syntheses and characterization of a series of compounds in the pentanary (five components) system AE-TeIV-TM-O-X (AE=alkaline earth metal, TM=transition metal and X=halogen), in which nine new compounds were found. The crystal structures of each of these compounds were determined by the single crystal X-ray diffraction data.

No description available.

Graphitische Karbonitride sind organische, kovalent gebundene, geschichtete und kristalline Halbleiter mit einer hohen thermischen und chemischen Stabilität. Diese Eigenschaften machen 2D Schichten der graphitischen Kristalle potentiell nützlich für das Ziel, Limitationen von organischen 0D Molekularen und 1D polymerischen Halbleitern zu überwinden. Trotz dieser interessanten Eigenschaften haben nur wenige Publikationen erfolgreich graphitische Karbonitride in optoelektronischen Bauteilen eingesetzt. Um die Vorteile dieser Materialien nutzbar zu machen, wurden bessere Synthesebedingungen gesucht. Die Verwendung von einem Iod-Eutektikum zeigt, dass Anionen mit einem größeren Radius als Bromid nicht für die Stabilisation von graphitischen Karbonitriden geeignet sind. Das Optimieren der Synthesebedingungen von Poly(triazin-imid)-LiBr resultiert in der Reduzierung von einem kohlenstoffreichen Zersetzungsprodukt bei vollständiger Kondensation. Das Untersuchen der elektronischen Struktur mit ab initio Berechnungen ergibt, dass der elektronische VB-CB-Übergang verboten ist. Dies resultiert daraus, dass die Zustände des obersten Valenzbandes nichtbindender Natur sind. Ein Band aus nichtbindenden Elektronen als oberstes Valenzband ist vor allem aus „lone-pair semiconductors“ aus der sechsten Hauptgruppe bekannt. In der Welt organischer Halbleiter wurde dieses Phänomen bisher nicht beobachtet. Die geringe makroskopische elektrische Leitfähigkeit der PTI-Filme wurde mit der Leitfähigkeit auf Nanoebene verglichen, woraus gefolgert werden kann, dass der Ladungsträgertransport durch den nanokristallinen Charakter an den Kristall-Kristall Übergängen gestört wird. Die elektronische Leitfähigkeit, Mobilität der Ladungsträger sowie die Ladungsträgerdichte wurden untersucht. Die Energie Niveaus legen nahe das Elektronentransport in der Präsenz von Sauerstoff möglich ist. Die erste Applikation eines kovalenten organischen Netzwerks in einer organischen lichtemittierenden Diode ist gezeigt worden. / Graphitic carbon nitrides are organic covalently-bonded, layered, and crystalline semiconductors with high thermal and oxidative stability. These properties make 2D layers of graphitic carbon nitrides potentially useful in overcoming the limitations of 0D molecular and 1D polymer semiconductors. Only few reports have shown them being employed in optoelectronic applications. With the goal to find better reaction conditions that enable higher product quality from the ionothermal synthesis the size effect of anions is studied by using an iodide eutectic instead of bromide or chloride eutectic. The highest crystalline condensation product obtained is melem, revealing that the large iodide anion is not capable of stabilizing a graphitic structure. Studying the synthesis conditions of poly(triazine imide) (PTI), the best characterized graphitic carbon nitride in literature, it is revealed that the brown discoloration of the product is due to a carbon rich side product. Reduction of reaction temperature and increase of reaction time allows omittance of carbonisation. Analyzing the electronic structure with ab initio calculations one finds that the lowest energy electronic transition in PTI is forbidden due to a non-bonding uppermost valence band. A uppermost non-bonding valence band is most reminiscent of lone-pair semiconductors and unknown in the world of organic semiconductors making PTI the first organic lone-pair semiconductor. The low electrical conductivity of PTI derivatives is compared to nanoscale conductivity values. The results indicate that macroscopic conductivity is hampered by the nano-crystalline character due to charge carrier trapping at crystal interfaces. The effective mobility is in the range of amorphous organic semiconductors with an unexpectedly high carrier density. The energy levels in PTI-LiBr potentially enable environmentally stable n-transport. The first successful Application of a covalent organic framework in a organic light emitting diode is presented.