Unusual structural phenomena in the reaction of copper and nickel dihalides with NH_3(g) at ambient conditions

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Zinc germanium nitrides and oxide nitrides: the influence of oxygen on electronic and structural properties

Zinc containing ternary nitrides, in particular ZnSnN2 and ZnGeN2, have great potential as earth-abundant and low toxicity light-absorbing materials. The incorporation of oxygen in this system – may it be intentional or unintentional – affects the crystal structure of the materials as well as their optical band gaps. Herein, we explore the origins of structural changes between the wurtzite type and its hettotype, the β-NaFeO2 type, and highlight the effect of oxygen. Furthermore, we study the electronic structure and bonding in order to understand the reason for the narrower band gap of zinc germanium oxide nitrides as opposed to pure zinc germanium nitride

A contribution towards the performance and structural understanding of copper and nickel salts as ammonia stores

The ongoing depletion of fossil fuels and the severe consequences of the greenhouse effect make the development of alternative energy systems crucially important. While hydrogen is, in principle, a promising alternative, releasing nothing but energy and pure water. Hydrogen storage is complicated and no completely viable technique has been proposed so far. This work is concerned with the study of one potential alternative to pure hydrogen: ammonia, and more specifically its storage in solids. Ammonia, NH3, can be regarded as a chemical hydrogen carrier with the advantages of strongly reduced flammability and explosiveness as compared to hydrogen. Furthermore, ammine metal salts presented here as promising ammonia stores easily store up to 50 wt.-% ammonia, giving them a volumetric energy density comparable to natural gas. The model system NiX2–NH3 ( X = Cl, Br, I) is studied thoroughly with respect to ammine salt formation, thermal decomposition, air stability and structural effects. The system CuX2–NH3 ( X = Cl, Br) has an adverse thermal decomposition behaviour, making it impractical for use as an ammonia store. This system is, however, most interesting from a structural point of view and some work concerning the study of the structural behaviour of this system is presented. Finally, close chemical relatives to the metal ammine halides, the metal ammine nitrates are studied. They exhibit interesting anion arrangements, which is an impressive showcase for the combination of diffraction and spectroscopic information. The characterisation techniques in this thesis range from powder diffraction over single crystal diffraction, spectroscopy, computational modelling, thermal analyses to gravimetric uptake experiments. Further highlights are the structure solutions and refinements from powder data of (NH4)2[NiCl4(H2O)(NH3)] and Ni(NH3)2(NO3)2, the combination of crystallographic and chemical information for the elucidation of the (NH4)2[NiCl4(H2O)(NH3)] formation reaction and the growth of single crystals under ammonia flow, a technique allowing the first documented successful growth and single crystal diffraction measurement for [Cu(NH3)6]Cl2

A thorough investigation of the crystal structure of willemite-type Zn2GeO4

The thermodynamically stable phase of Zn2GeO4 contains tetrahedrally coordinated cations only and crystallizes isostructurally to Zn2SiO4 (willemite, space group R3? , no. 148). While this material is considered for a plethora of energy-related applications, such as transparent conducting oxide, battery material and photocatalyst, cation ordering in the crystal structure has not been investigated thoroughly. We have therefore re-determined the crystal structure of Zn2GeO4 using a combination of X-ray and neutron powder diffraction. The additional neutron diffraction study helps to distinguish between the isoelectronic Zn2+ and Ge4+ cations and yields valuable information about a partial or complete cation permutation in this material. The experimental study is supported by first-principles calculations on the structural properties of Zn2GeO4 utilizing a standard generalized gradient approximation, and the more accurate hybrid functional HSE06. In order to better understand cation permutations, additional calculations including defective Zn2GeO4 have been performed based on a supercell approach. Our results show that, with the preparation conditions applied, cation permutation is unlikely to occur in our samples

Ni(NH3)2(NO3)2 – A 3-D network through bridging nitrate units isolated from the thermal decomposition of nickel hexammine dinitrate

Nickel nitrate diammine, Ni(NH3)2(NO3)2, can be synthesised from the thermal decomposition of nickel nitrate hexammine, Ni[(NH3)6](NO3)2. The hexammine decomposes in two distinct major stages; the first releases 4 equivalents of ammonia while the second involves the release of NOx, N2, and H2O to yield NiO. The intermediate diammine compound can be isolated following the first deammoniation step or synthesised as a single phase from the hexammine under vacuum. Powder X-ray diffraction (PXD) experiments have allowed the structure of Ni(NH3)2(NO3)2 to be solved for the first time. The compound crystallises in orthorhombic space group Pca21 (a = 11.0628 (5) Å, b = 6.0454 (3) Å, c = 9.3526 (4) Å; Z = 4) and contains 11 non-hydrogen atoms in the asymmetric unit. Fourier transform infrared (FTIR) spectroscopy demonstrates that the bonding in the ammine is consistent with the structure determined by PXD

Ni(NH3)2(NO3)2 – A 3-D network through bridging nitrate units isolated from the thermal decomposition of nickel hexammine dinitrate

Nickel nitrate diammine, Ni(NH3)2(NO3)2, can be synthesised from the thermal decomposition of nickel nitrate hexammine, Ni[(NH3)6](NO3)2. The hexammine decomposes in two distinct major stages; the first releases 4 equivalents of ammonia while the second involves the release of NOx, N2, and H2O to yield NiO. The intermediate diammine compound can be isolated following the first deammoniation step or synthesised as a single phase from the hexammine under vacuum. Powder X-ray diffraction (PXD) experiments have allowed the structure of Ni(NH3)2(NO3)2 to be solved for the first time. The compound crystallises in orthorhombic space group Pca21 (a = 11.0628 (5) Å, b = 6.0454 (3) Å, c = 9.3526 (4) Å; Z = 4) and contains 11 non-hydrogen atoms in the asymmetric unit. Fourier transform infrared (FTIR) spectroscopy demonstrates that the bonding in the ammine is consistent with the structure determined by PXD

Uncovering cation disorder in ternary Zn1+xGe1−x(N1−xOx)2 and its effect on the optoelectronic properties

Ternary nitride materials, such as ZnGeN2, have been considered as hopeful optoelectronic materials with an emphasis on sustainability. Their nature as ternary materials has been ground to speculation of cation order/disorder as a mechanism to tune their bandgap. We herein studied the model system Zn1+xGe1−x(N1−xOx)2 including oxygen – which is often a contaminant in nitride materials – using a combination of X-ray and neutron diffraction combined with elemental analyses to provide direct experimental evidence for the existence of cation swapping in this class of materials. In addition, we combine our results with UV-VIS spectroscopy to highlight the influence of disorder on the optical bandgap

A metamorphic inorganic framework that can be switched between eight single-crystalline states

The design of highly flexible framework materials requires organic linkers, whereas inorganic materials are more robust but inflexible. Here, by using linkable inorganic rings made up of tungsten oxide (P8W48O184) building blocks, we synthesized an inorganic single crystal material that can undergo at least eight different crystal-to-crystal transformations, with gigantic crystal volume contraction and expansion changes ranging from −2,170 to +1,720 Å3 with no reduction in crystallinity. Not only does this material undergo the largest single crystal-to-single crystal volume transformation thus far reported (to the best of our knowledge), the system also shows conformational flexibility while maintaining robustness over several cycles in the reversible uptake and release of guest molecules switching the crystal between different metamorphic states. This material combines the robustness of inorganic materials with the flexibility of organic frameworks, thereby challenging the notion that flexible materials with robustness are mutually exclusive