Zur Chemie des Chlortrifluorids und der Fluoride des Urans, Neptuniums und Plutoniums

The reactions of chlorine trifluoride with a variety of compounds were studied in the course of this work. The reactions of alkali metal fluorides with liquid chlorine trifluoride at room temperature lead to the formation of alkali metal tetrafluoridochlorates(III), A[ClF4] (A = K, Rb, Cs). Their crystal structures were determined for the first time and they indicate the presence of planar (almost) square tetrafluoridochlorate(III) anions. Vibrational spectra of the compounds show, that hydrogen fluoride adducts of the alkali metal fluorides occur as impurities. The reaction of cesium fluoride with an excess of chlorine trifluoride leads to the formation of a salt with a polynuclear fluoridochlorate(III) anion. The propeller-shaped [Cl3F10]− anion is obtained in the Cs[Cl3F10] salt. The crystal structure of this compound can be regarded as a representative of the rare A[5]B[5] structure type. Quantum-chemical calculations for [X3F10]− anions in the gas-phase indicate ionic or polar, covalent X−F bonds. The reactions of metal powders, fluorides, or chlorides with an excess of chlorine trifluoride lead to the formation of difluorochloronium(III) salts if the starting material can form a stable fluoridometallate anion. A bent ClF2+ cation is present in the crystal structures of these compounds and a variety of structural motifs are observed. They range from molecular building blocks to linear, zig-zag, or helical chains. Reactions of oxides, metal powders, or chlorides with chlorine trifluoride, and in some cases additional oxygen, under photochemical conditions lead to the formation of difluorooxychloronium(V) salts. The starting material has to have the ability to form stable fluoridometallate or fluoridooxidometallate anions. Pyramidal ClOF2+ cations are present in the crystal structures and the Cl−O and Cl−F distances within these cations strongly depend on the anion. Dioxychloronium(V) salts can be obtained from the hydrolysis reactions of difluorochloronium(III) compounds, or, if the starting material can form a stable fluoridometallate or fluoridooxidometallate anion, from the reaction of oxides with chlorine trifluoride. The Lewis acid properties of uranium pentafluoride were studied in another project. Fluoridouranates(V) were obtained from reactions of fluoride ion donors such as strontium or barium fluoride, or hydrazinium difluoride with uranium pentafluoride in anhydrous hydrogen fluoride. The obtained compounds show novel structure motifs, which were previously unknown for the fluoridouranates(V). An isolated anion is observed in the salt Sr[UF5(HF2)2], a dinuclear one in Sr[U2F12], and more complex, layer-like anions in the salts Ba(HF)2U2F12 and (N2H6)U2F10(HF2)2. The reaction of uranium hexafluoride with sulfur in anhydrous hydrogen fluoride leads to the formation of uranium tetrafluoride, which can be obtained in pure form after removal of volatiles in vacuo. It has a high purity and is free from oxidic or sulfidic impurities. Under the impact of high pressure and temperature, a novel high-pressure modification of uranium tetrafluoride could be obtained. Hp-UF4 shows a complex structure. The reaction of neptunium or plutonium dioxide with fluoride ion donors in hydrofluoric acid at room temperature or hydrofluorothermal conditions leads to the formation of single-crystalline fluoridometallates(IV). The characterized compounds are isotypic with the respective uranium compounds and the actinoid fluorine distances tend to decrease with increasing atomic number, which is likely due to the actinoid contraction. Single-crystalline rubidium heptafluoridouranate(VI) could be obtained from the oxidation of the hexafluoridouranate(V) RbUF6 with chlorine trifluoride. Isolated [UF7]− anions are present in the crystal structure, which could be structurally characterized for the first time.