The hydroflux method is a promising new synthesis approach for explorative crystal growth. Various new compounds were synthesized during the preparation of this PhD thesis, doubling the number of substances discovered to date via the hydroflux approach. The product range consists primarily of oxides, hydroxides or a mixture of both, with oxygen-free compounds being obtained for the first time in form of various chalcogenides. The so far barely explored redox chemistry of the hydroflux was elucidated in more detail and novel preparation procedures were developed to intentionally introduce reductive and oxidative conditions. Thus, chalcogenides and highly oxidized cations were obtained. In addition, important reaction parameters of the hydroflux method were derived based on the developed syntheses procedures and properties of the various new compounds. The two largest compound classes within the product range are the hydrogarnets and the oxo(hydroxo)ferrates. Among the various interesting properties of the latter compounds, the potassium ion conductivity stands out, which is closely related to their structure and chemical stability. The structure of the oxohydroxoferrates K2–x(Fe,M)4O7–y(OH)y (M = Fe, Si, Ge, Ti, Mn, Ir) can be described as a parking garage. Honeycomb layers consisting of edge-sharing [FeO6] octahedra form the floors, which are connected by pairs of vertices-sharing [FeO4] tetrahedra representing the pillars. In the pictorial representation of this two-dimensional ion conductor, the potassium ions represent the cars that are mobile within one floor because not all parking lots are occupied, i.e., the structure has a potassium deficit. The substituted elements M influence the potassium content and thus the ion conductivity, which tends to increase with higher potassium deficits. The oxohydroxoferrates hydrolyze slowly in moist air under segregation of potassium hydroxide, which significantly increases the mobility of the potassium ions due to the hygroscopic nature and thus the ion conductivity. The three-dimensional ion conductor K12+6xFe6Te4–xO27 consists of a cubic labyrinth of potassium channels, which are surrounded by an open framework of [FeO5] pyramids and [TeO6] octahedra. Every potassium position is connected with eight large cavities acting as nodes for the potassium channels. However, the potassium positions within the channels are fully occupied, which hinders mobility within the labyrinth to the disadvantage of the ion conductivity. Similar to K2–x(Fe,M)4O7–y(OH)y, K12+6xFe6Te4–xO27 hydrolyzes under ambient conditions decreasing the potassium content within the structure. However, only a slight amount of potassium can be removed before the open framework collapses. Hydrogarnets crystallize in the flexible garnet structure-type and adapt the general formula AE3[M(OH)6]2. The crystal structure consists of a complex three-dimensional framework, in which [MO6] octahedra and empty (O4H4)4– tetrahedra are connected via their vertices and the larger alkaline earth metal cations AE filling the remaining voids. In contrast to garnets (nesosilicates), the hydrogarnets have a lower thermal stability and hardness. For many applications, this instability might be a drawback, but at the same time, it qualifies them for a low temperature and resource efficient application as carbon-free single-source precursors. In case of the rare earth hydrogarnets (AE = Sr, Ba; M = Sc, Y, Ho–Lu), the dehydration at about 550 °C leads to the formation of AEM2O4, which were previously obtainable only at reaction temperatures above 1300 °C.[86–89] Redox chemistry in hydroflux systems had been barely investigated so far, with neither equations nor possible mechanisms discussed to explain redox phenomena. In more than half of the published articles of this thesis, redox reactions were observed, often involving molecular oxygen or nitrate as oxidant. Similar to alkali metal hydroxide melts, molecular oxygen is expected to react with hydroxide ions to form peroxides or even superoxides, while nitrates might be reduced to nitrites. Moreover, higher oxidations states seem to be preferred in the hydroflux medium, as, for example, tellurium(IV), chromium(III) and arsenic(III) were readily oxidized to their maximum oxidation states. Additionally, the partial replacement of KOH by KO2 in the hydroflux medium introduced a high oxygen partial pressure, resulting in the oxidation of iodide(–I) ions to orthoperiodate(VII) ions. This preparation procedure has a great potential to yield compounds with elements in unusual high oxidation states, especially transition metals. The tendency of some elements to prefer higher oxidation states than usual was utilized to intentionally introduce reductive conditions. With this approach, reduction of selenium(IV) and tellurium(IV) oxides to their chalcogenides was achieved by using arsenic(III) oxide as reducing agent. In solution, monochalcogenide and dichalcogenide anions as well as the new (SeTe)2– anions were obtained. In addition, millimeter-sized crystals of the chalcogenides K2Se3 and K2Te3 and the previously unknown K2Se2Te were crystallized. This unexpected redox chemistry is far from what the standard potentials would suggest. The activity of water is considerably reduced by the ultra-alkaline conditions, which does not only decrease its vapor pressure and drives the reaction but obviously prevents the hydrolysis of the water sensitive chalcogenides. Overall, a preparatively simple, time-saving and secure approach compared to traditional methods like the synthesis in liquid ammonia was developed. Moreover, this method allows known and new potassium trichalcogenides to be obtained in larger amounts and in form of millimeter-sized single-crystals. A transfer of the approach to other systems should be promising. Reaction parameters described in literature were mostly confirmed and some details were added. For example, the selection of mineralizers was extended, reaction times and temperatures were specified, and a method for purifying the reaction products was added. With the exception of base concentration and concentration-dependent product formation, both of which have barely been studied so far. An example is the iron(III)-KOH hydroflux system, where four different products are accessible with increasing base-concentrations: α-Fe2O3, K2–xFe4O7–x(OH)x, K2Fe2O3(OH)2 and KFeO2. Overall, two trends are evident with increasing base concentration. First, the alkali metal content within the product rises or the alkali metal is incorporated in the structure in the first place. Second, the hydrogen content of the products constantly decreases. The latter is attributed to the increasing hygroscopicity of the reaction medium at higher hydroxide concentrations, which also reduces the activity of water in the hydroflux medium, so that water-sensitive compounds are stabilized.

Oxygenierungs- und Oxidationsreaktionen sind in unserem Alltag allgegenwärtig und von großer Bedeutung. Sie finden Anwendung von der Natur bis hin zur Industrie. Der Einsatz von O2 als Sauerstoffquelle bzw. Oxidationsmittel ist besonders erstrebenswert. Die Erforschung der Aktivierung von O2 an Übergangsmetallkomplexen und Untersuchung der Reaktivität der resultierenden Verbindung ist von großer Bedeutung für das Verständnis dieser Reaktionen und Mechanismen. In dieser Arbeit wurde zunächst der Komplex trans-[Ir(4-C5F4N)(CNtBu)(PiPr3)2] synthetisiert, welcher mit dem 4-C5F4N- und dem CNtBu-Liganden stabilisierende Komponenten und wertvolle analytische Sonden enthält. Ausgehend von dieser Iridium(I)-Verbindung konnte auf verschiedenen Wegen der Peroxidokomplex trans-[Ir(4-C5F4N)(O2)(CNtBu)(PiPr3)2] erhalten und umfangreich charakterisiert werden. In Gegenwart von [Fe(C5H5)2][PF6] konnten Hinweise auf einen redoxkatalysierten Mechanismus gewonnen werden. Im nächsten Abschnitt konnte gezeigt werden, dass sich der Peroxidokomplex durch Bronstedsäuren aktivieren lässt. So wurde z.B. unter der Verwendung von Säuren wie HCl, CF3COOH oder HF die Bildung von H2O2 erzielt. Dabei entstehen die entsprechenden Iridium(III)-Komplexe mit den koordinierten Säureanionen. In Gegenwart von HCOOH werden ein Carbonatokomplex und H2 als Hauptprodukte gebildet und es konnten Hinweise zum Mechanismus dieser komplexen Reaktion gewonnen werden. Des Weiteren sind Lewissäuren und Elektrophile in der Lage, die metallgebundene Disauerstoffeinheit des Peroxidokomplexes zu aktivieren. Dazu wurden unter Anderem Silane und Borane eingesetzt. Im Fall von ClSiMe3 und BClCy2 konnten während der Reaktion Intermediate detektiert und analysiert werden. Tragen die Lewissäuren Chloratome wird die entsprechende Dichloridoiridium(III)-Verbindung gebildet. Durch Einsatz von BPh3 konnte eine veränderte Reaktivität erreicht werden und der Ausgangskomplex trans-[Ir(4-C5F4N)(CNtBu)(PiPr3)2] zurückerhalten werden. / Oxygenation- and oxidation reactions are ubiquitous and of great importance to our daily life. They find application from nature to industry. The use of O2 as an oxygen source or oxidation reagent, respectively, is particularly desirable. The research on the activation of O2 at transition metal complexes and the investigations of the reactivity of the resulting compounds is of great significance for the understanding of these reactions and mechanisms. Herein, this work describes the synthesis of the complex trans-[Ir(4-C5F4N)(CNtBu)(PiPr3)2], which incorporates stabilizing and valuable analytical elements provided by the 4-C5F4N and CNtBu ligands. Starting from this iridium(I) compound, the peroxido complex trans-[Ir(4-C5F4N)(O2)(CNtBu)(PiPr3)2] could be synthesized using different methods. In the presence of [Fe(C5H5)2][PF6], indications for a redox catalyzed mechanism could be provided. The next chapter shows that Bronsted acids are capable of activating the peroxido complex. With the help of acids like HCl, CF3COOH or HF, for example, the formation of H2O2 was achieved. Thereby, the corresponding iridium(III) complexes with the coordinating anions are formed. In the presence of HCOOH, a carbonato complex and H2 are formed as main products and ideas for the mechanism of this complex reaction were indicated. Furthermore, Lewis acids and electrophiles have the ability to activate the metal bound dioxygen moiety of the peroxido complex. Silanes and boranes were used for this purpose amongst others. In case of ClSiMe3 and BClCy2, intermediates of the reactions could be detected and analysed. If the Lewis acids carry chloride atoms, the corresponding dichlorido iridium(III) compounds were formed. BPh3 enabled a different reactivity and allowed the isolation of the starting material trans-[Ir(4C5F4N)(CNtBu)(PiPr3)2].