Oxidative hydrogenation of polyanions with gallium, silicon, germanium and tin - functional materials by subtle redox chemistry

Zintl相是碱性或碱土金属M与13-16族元素E之间的化合物，通常含有带有共价E-E键的多阴离子[Ex-]n。氢可以通过氧化这些聚阴离子从而增加它们的连通性来反应，也可以通过在聚阴离子上插入或添加氢来反应。在之前的一个项目中，建立了主族元素-元素和元素-氢键形成的初步规则。通过原位x射线和中子粉末衍射、电子显微镜、热分析、固体核磁共振波谱、全中子散射、量子力学建模和拉曼光谱等方法，对具有硅和锗之链的Zintl相（M = Ca, Sr, Ba; E = Si, Ge）的加氢过程进行了研究，发现了新的Zintl相氢化物（MEH4/3、MEH5/3和MEH6/3）与缩合的含氢阴离子和含氢量较低的中间体。在M(I)-M(II)-M（III）系列中，即碱-碱土-稀土，H原子的化学键由共价键转变为离子键和金属键。在本项目中，我们将完善这一经验法则，用于Zintl相的加氢反应，使我们能够合理化氢化Zintl相的存在、热力学稳定性、化学键、晶体和电子结构以及氢容量。最初将通过上述方法研究约45种具有E = Ga, Si, Ge， Sn和M =碱-碱-稀土或其中两种的混合物的MxEy化合物，这些化合物具有各种阴离子（之字形链，螺旋，五元环和六元环，哑铃，1D带状和3D网）。对E-E和E-H键形成规则的详细了解将使我们能够预测Zintl相的进一步氢化反应，即允许通过与氢氧化来调整Zintl相氢化物的聚阴离子的连性。探索在储氢材料和低维材料制备方面的潜力。一方面，将测试Zintl相作为储氢材料的实际应用。通过体积法和重量法，将研究CaSi储氢的热力学、动力学、可逆性和可循环性，并在项目的第一部分确定进一步的候选材料。另一方面，Zintl相氢化物将被用作1D和2D材料的前驱体。水解、氨解和甲基化反应可生成1D和2D聚合物，这可能是硅烷、日耳曼烷和锡烷或相关材料的有趣中间体。本课题所开发的氢对聚阴离子的控制氧化，在固体结构、电子和磁性能的微调方面具有很大的潜力。该项目的研究结果有望促进含有三价金属和四价金属多阴离子化合物的材料相关研究，特别是镓、硅、锗、锡。

Zintl phases are compounds between an alkaline or alkaline earth metal M with an element E of group 13-16 and usually contain polyanions [Ex-]n with covalent E-E bonds. Hydrogen may react either by oxidizing these polyanions thus increasing their connectivity or by insertion or addition of hydrogen to the polyanions. In a previous project, preliminary rules for the formation of main group element-element and element-hydrogen bonds were established. The hydrogenation of Zintl phases with silicon and germanium zigzag chains (ME with M = Ca, Sr, Ba; E = Si, Ge) by in situ X-ray and neutron powder diffraction, electron microscopy, thermal analysis, solid-state nuclear magnetic resonance spectroscopy, total neutron scattering, quantum-mechanical modelling and Raman spectroscopy revealed new Zintl phase hydrides (MEH4/3, MEH5/3 and MEH6/3) with condensed hydrogen-containing polyanions and intermediates with lower hydrogen content. In the series M(I)-M(II)-M(III), i. e. alkali-alkaline earth-rare earth, the chemical bonding of H atoms shifts from covalent to ionic and metallic. In this project, we will refine this rule-of-thumb for hydrogenation reactions of Zintl phases, enabling us to rationalize existence, thermodynamic stability, chemical bonding, crystal and electronic structure, and hydrogen capacity of hydrogenated Zintl phases. Initially about 45 compounds MxEy with E = Ga, Si, Ge, Sn and M = alkali-alkaline earth-rare earth or a mixture of two of them, featuring various polyanions (zigzag chains, helices, five- and six-membered rings, dumb-bells, 1D ribbons and 3D nets) will be studied by the above mentioned methods. The detailed knowledge of the rules governing the formation of E-E and E-H bonds will enable us to predict further hydrogenation reactions of Zintl phases, i. e. allow for a connectivity tuning in polyanions of Zintl phase hydrides by oxidation with hydrogen. The potential in the preparation of materials for hydrogen storage and low-dimensional materials shall be explored. On one hand, practical aspects of Zintl phases as hydrogen stores will be tested. By volumetric and gravimetric method, thermodynamics, kinetics, reversibility and cycleability for hydrogen storage will be studied for CaSi and further candidates identified in the first part of the project. On the other hand, Zintl phase hydrides will be used as precursors for 1D and 2D materials. Hydrolysis, ammonolysis and methylation reactions may lead to 1D and 2D polymers, which could be interesting intermediates to silicane, germanane, and stannanane or related materials. The controlled oxidation of polyanions by hydrogen, to be developed in this project, has got a great potential for the fine tuning of structural, electronic and magnetic properties of solids. The results of this project are expected to stimulate materials related research with compounds containing polyanions of triels and tetrels, especially gallium, silicon, germanium, tin.