Preparation of intermetallic phases in ionic liquids

在低温下制备金属间相仍然是一项具有挑战性的任务。在过去的几年中，反应性金属间化合物前体的氧化还原反应已经发展成为一种通用的方法，特别是提供亚稳金属间化合物相。到目前为止，反应主要是作为非均相气-固反应进行的。此外，在Zintl相的氨或有机胺溶液中的簇物种上的低温氧化还原反应提供了获得新的准金属物种如簇聚合物的途径。但是，在大多数情况下，已经获得了含有溶剂分子或络合阳离子的相。在这方面，作为金属间前体的溶剂的离子液体中的氧化还原反应可能提供新的纯金属间相的替代途径。然而，到目前为止，这些尝试受到所应用的离子液体对高反应性前体如Zintl相的过高反应性的影响，导致快速且难以控制大部分非均相氧化成无定形产物。该项目一方面旨在开发能够在低温下溶解含有Zintl簇的金属间相的惰性离子液体，并通过添加合适的氧化剂系统地研究由此可能的受控均相氧化还原反应以形成新的亚稳金属间相。这种氧化还原反应在离子液体中的盐状碳化物的适用性也将被研究，有希望的制备新的碳化物，甚至元素碳修饰与聚合物结构图案。此外，将在有目的地合成的离子液体中研究相应金属间前体的拓扑结构氧化还原反应，所述离子液体具有合适的反应性和足够的溶解能力，以使前体相能够完全转化，并提供技术上感兴趣但难以获得的产物种类，例如石墨烯类似的硅片。在本项目的研究中，将合成所谓的TAAIL（可调烷基-芳基离子液体），其咪唑鎓阳离子携带官能化苯基取代基，能够进行电子调节，从而改变作为质子源的反应性。烷基侧链将被阴离子或聚醚基团官能化，通过阳离子的络合增强盐或盐样相的溶解度。此外，这种离子液体的质子活性将通过咪唑核的碳原子上的氢与惰性芳基取代基的选择性交换来调节。

The preparation of intermetallic phases at low temperatures continues to be a challenging task. During the past years, redox reactions of reactive intermetallic precursors have been developed to a versatile method providing access particularly to metastable intermetallic phases. The reactions so far have been conducted mostly as heterogeneous gas-solid reactions. Additionally, low-temperature redox reactions on cluster species in ammonia or organic amine solutions of Zintl phases provide access to new metalloid species such as cluster polymers. But, in most cases, phases containing solvent molecules or complex cations have been obtained. In that respect, redox reactions in ionic liquids acting as a solvent for the intermetallic precursors might provide an alternative route to new purely intermetallic phases. However, such attempts so far have suffered from a too high reactivity of the applied ionic liquids towards highly reactive precursors such as Zintl phases, resulting in a fast and difficult to control mostly heterogeneous oxidation to amorphous products. This project, on the one hand, aims to develop inert ionic liquids capable of dissolving intermetallic phases containing Zintl clusters at low temperatures and to systematically study thus possible controlled homogeneous redox reactions to new metastable intermetallic phases by addition of suitable oxidizing agents. The applicability of such redox reactions in ionic liquids on salt-like carbides will be investigated as well, promising the preparation of new carbides or even elemental carbon modifications with polymeric structural motifs. Furthermore, topotactic redox reactions of respective intermetallic precursors will be investigated in purposefully synthesized ionic liquids of suitable reactivity and sufficient dissolution capability for product species to enable complete conversion of the precursor phase and to provide access to technically interesting yet otherwise hardly accessible product species such as graphene-analogous silicon sheets. For the studies within this project, so called TAAILs (Tunable Alkyl-Aryl Ionic Liquids) will be synthesized, the imidazolium cations of which carry functionalized phenyl substituents enabling electronic tuning and thus modification of the reactivity as proton source. The alkyl side chains will be functionalized by anionic or polyether groups enhancing solubility of salts or salt-like phases by complexation of cations. Furthermore, the protic activity of such ILs will be tuned by selective exchange of the hydrogens on carbon atoms of the imidazole core against inert aryl substituents.