Hydroflux Syntheses — Reactions in Ultrabasic Media at Moderate Temperatures

氢通量合成，使用非常高浓度的碱性溶液，是一种有前途的新的时间，能量和原子效率的合成方法，特别是但不限于氧化物和氢氧化物。其条件不同于水热反应，也不同于碱盐熔体反应。先前的工作表明，可以反应的主族元素和过渡元素的范围，以及可以处理的氧化态，比最初预期的要宽得多。我们将探索氢通量合成的潜力，并进一步了解关键的反应参数和正在进行的化学过程。应确定所获得的固体产品的关键化学、结构和物理性质。我们将具体遵循两个方向。首先，流体通量中水的低活度为在中等温度下实现几乎无水的酸碱化学提供了选择。常见的无机酸及其酸酐会发生反应，目的是使不同程度的质子化和缩合的复合阴离子金属盐结晶。形成的化合物很可能是新化合物，具有非中心对称结构，并表现出非线性光学性质。其次，研究流体通量条件下的氧化还原化学。表中的电化学标准电位不再适用，特别是在依赖于ph的体系中。再加上流体通量的吸湿特性，这使得中间氧化态的可溶性金属氧酸盐成为意想不到的强还原剂，其潜力将被探索。另一方面，根据熔剂的pH值和碱金属阳离子，氧化物、过氧化物、超氧化物和分子氧之间存在活泼的氧化还原化学反应。通过使用固体氧源或过氧化氢溶液，可以以可控的方式增加氧化电位，这将被详细研究并用于稳定过渡金属的高氧化态。

Hydroflux synthesis, using very highly concentrated alkaline solutions, is a promising new time-, energy-, and atom-efficient synthesis approach, especially but not exclusively for oxides and hydroxides. The conditions differ from those in hydrothermal reactions as well as those in alkaline salt melts. Previous work has shown that the range of main-group and transition elements that can be reacted, as well as of the oxidation states that can be addressed, is much wider than initially expected. We will explore the potential of hydroflux synthesis and gain further knowledge about the crucial reaction parameters and the ongoing chemical processes. Key chemical, structural, and physical properties of the obtained solid products shall be determined. We will specifically follow two directions. First, the low activity of water in the hydroflux provides options for a virtually anhydrous acid-base chemistry at moderate temperature. Common mineral acids and their anhydrides will be reacted with the aim of crystallizing metal salts of complex anions with various degree of protonation and condensation. There is a high probability that the compounds formed are new, will have non-centrosymmetric structures and exhibit non-linear optical properties. Second, the redox chemistry under hydroflux conditions will be investigated. The tabulated electrochemical standard potentials no longer apply, particularly in systems that depend on pH. Together with the hygroscopic properties of hydroflux, this makes soluble oxometalates in intermediate oxidation states unexpectedly strong reducing agents whose potential will be explored. On the other hand, there is a lively redox chemistry between oxide, peroxide, superoxide and molecular oxygen depending on the pH and the alkali metal cation of the flux. By using solid oxygen sources or hydrogen peroxide solutions, the oxidation potential can be increased in a controlled manner, which will be studied in detail and exploited to stabilize high oxidation states of transition metals.