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。在过去的几年里，反应性金属间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相。迄今为止，这些反应大多以非均相气固反应的形式进行。此外，在氨或Zintl相的有机胺溶液中，簇状物质的低温氧化还原反应提供了新的类金属物质，如簇状聚合物。但是，在大多数情况下，已得到含有溶剂分子或络合阳离子的相。在这方面，离子液体中的氧化还原反应作为金属间前体的溶剂可能为新的纯金属间相提供另一种途径。然而，到目前为止，这种尝试受到离子液体对高活性前驱体（如Zintl相）的反应性过高的影响，导致大多数非均相氧化成非晶产品的速度快且难以控制。一方面，本项目旨在开发能够在低温下溶解含锌团簇的金属间相的惰性离子液体，并系统地研究通过添加合适的氧化剂，从而可能控制的均相氧化还原反应生成新的亚稳金属间相。离子液体中这种氧化还原反应在类盐碳化物上的适用性也将被研究，有望制备新的碳化物甚至具有聚合物结构基序的元素碳修饰。此外，各金属间前驱体的拓扑化氧化还原反应将在有目的地合成的离子液体中进行研究，这些离子液体具有合适的反应活性和足够的溶解能力，可以使前驱体相完全转化，并提供技术上有趣但难以获得的产品种类，如石墨烯类似硅片。在这个项目的研究中，所谓的tail（可调烷基芳基离子液体）将被合成，其咪唑阳离子携带功能化的苯基取代基，可以进行电子调谐，从而修饰质子源的反应性。烷基侧链将被阴离子或聚醚官能团官能团化，通过阳离子络合提高盐或类盐相的溶解度。此外，通过咪唑核碳原子上的氢与惰性芳基取代基的选择性交换，可以调节这种il的质子活性。

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.