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A chemical holy grail: the synthesis of helium and neon-containing compounds

化学圣杯：含氦和氖化合物的合成

基本信息

批准号：
EP/J021342/1
负责人：
Shengfu Yang
金额：
$ 52.6万
依托单位：
University of Leicester
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2012
资助国家：
英国
起止时间：
2012 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FJ021342%2F1
关键词：
chemical holy grail synthesis helium

项目摘要

A central quest of chemistry is to construct new compounds and synthesise entirely new links between atoms using the known elements as the building blocks. The only two long-lived elements in our universe that are not found in any known chemical compounds are helium and neon. Consequently, one of the greatest remaining challenges in the chemical sciences is to incorporate these elements into synthetic chemistry. However, current thinking is that this is impossible, since helium and neon are thought to have almost no propensity to form chemical bonds.The difficulties faced in forming compounds containing helium and neon atoms derives from their full and compact electronic shells. For example, helium has a full 1s orbital and is therefore resistive to covalent bond formation. It also has the highest first ionization energy of any neutral atom, and so is energetically unwilling to form ionic bonds. These are huge obstacles to any attempt to induce chemistry for helium, and they are largely shared by neon. Nevertheless, encouraging signs are derived from recent work on the chemistry of argon, another of the noble gases. In the past few years it has been shown that argon-containing compounds can be made using chemistry induced in solid argon matrices at very low temperatures. This work was driven initially by purely theoretical predictions but was shown subsequently to be experimentally viable. In particular, the formation of insertion compounds, such as HArF, was achieved using photochemical stimulation of HF in a low-temperature argon matrix. However, these compounds are metastable, i.e. are trapped in a potential energy well which lies above the dissociation limit that would regenerate bare argon atoms. It is therefore possible for these compounds to decompose rapidly. Recent theoretical predictions suggest that stable donor-acceptor compounds containing helium or neon atoms are possible. The ideal acceptor molecule contains an energetically accessible orbital vacancy combined with a substantial dipole moment, which serves to stabilise any interaction with the helium or neon atom. Molecules with the right properties include transition metal halides such as AgF and CuF. Calculations suggest that adduct compounds, such He-CuF, can form spontaneously, with He-Cu binding energies of approximately 30 kJ/mol. Even stronger bonds, approaching 100 kJ/mol, are predicted to be achievable if so-called dipole-encapsulated species, such as NaF-He-CuF are formed. Thus we have a potential route to helium and neon chemistry, but the challenge then becomes how to put this into practice.Here we propose a novel strategy to access this new and profound chemistry. In the case of helium compounds, we propose to synthesise both adduct and dipole-encapsulated compounds using the unique environment provided by helium nanodroplets. Molecules can be added to helium nanodroplets by pick-up of gases, and in the case of metal fluorides these can be formed by oven evaporation. At that point the unique properties of helium nanodroplets kick-in, which include the ultra-low temperature (0.4 K) and rapid cooling, all within a liquid environment. It is therefore possible to bring the metal fluorides into gentle contact with helium using this approach. Furthermore, the low temperature liquid environment provides a means of using long-range dipole forces to steer two metal fluorides into the correct orientation for dipole-encapsulation of a helium atom. Once the compounds have formed, the helium droplets provide another benefit: a convenient means for detecting the new compounds using IR depletion spectroscopy. In the case of neon compounds we will adopt a different experimental approach which exploits low temperature solid neon matrices to form both adduct and dipole-encapsulated compounds.We believe that the work proposed here is internationally-leading and will deliver a paradigm change in chemistry.

化学的一个中心任务是构建新的化合物，并使用已知元素作为构建单元合成原子之间的全新连接。在我们的宇宙中，只有两种在任何已知的化合物中都没有发现的长寿元素是氦和氖。因此，化学科学中最大的挑战之一是将这些元素纳入合成化学。然而，目前的想法是这是不可能的，因为氦和氖被认为几乎没有形成化学键的倾向。形成含有氦和氖原子的化合物所面临的困难来自于它们完整而紧凑的电子壳层。例如，氦有一个完整的1 s轨道，因此不容易形成共价键。它也具有任何中性原子中最高的第一电离能，因此在能量上不愿意形成离子键。这些都是任何试图诱导氦化学的巨大障碍，它们在很大程度上被氖所共享。尽管如此，最近对另一种稀有气体氩的化学研究还是出现了令人鼓舞的迹象。在过去的几年中，已经表明，含氩化合物可以在非常低的温度下在固体氩基质中使用化学诱导来制备。这项工作最初是由纯粹的理论预测推动的，但随后被证明在实验上是可行的。特别是，形成的插入化合物，如HArF，实现了使用HF在低温氩气基质中的光化学刺激。然而，这些化合物是亚稳态的，即被困在高于解离极限的势能阱中，该解离极限将再生裸露的氩原子。因此，这些化合物可以迅速分解。最近的理论预测表明，含有氦或氖原子的稳定的供体-受体化合物是可能的。理想的受体分子包含一个能量可达的轨道空位，结合大量的偶极矩，用于稳定与氦或氖原子的任何相互作用。具有合适性质的分子包括过渡金属卤化物，如AgF和CuF。计算表明，加合物，如He-CuF，可以自发形成，与He-Cu结合能约为30 kJ/mol。甚至更强的键，接近100 kJ/mol，预计是可以实现的，如果所谓的偶极封装的物种，如NaF-He-CuF形成。因此，我们有一个潜在的途径，氦和氖化学，但挑战是如何将其付诸实践。在这里，我们提出了一个新的战略，以访问这个新的和深刻的化学。在氦化合物的情况下，我们建议使用氦纳米液滴提供的独特环境来合成加合物和偶极封装的化合物。分子可以通过吸收气体添加到氦纳米液滴中，并且在金属氟化物的情况下，这些可以通过烘箱蒸发形成。在这一点上，氦纳米液滴的独特性质，包括超低温（0.4 K）和快速冷却，都在液体环境中发挥作用。因此，可以使用这种方法使金属氟化物与氦气温和接触。此外，低温液体环境提供了一种使用长程偶极力将两种金属氟化物转向正确取向以用于氦原子的偶极封装的方法。一旦化合物形成，氦滴就会提供另一个好处：使用红外耗尽光谱法检测新化合物的方便方法。在氖化合物的情况下，我们将采用不同的实验方法，利用低温固体氖基质形成加合物和偶极包封的化合物。我们相信，这里提出的工作是国际领先的，并将提供化学的范式变化。