Intermetallic and Extraordinary Bonds of Beryllium and the Alkaline Earth Metals

在这个由化学系化学结构、动力学和机理a （CSDM-A）项目支持的项目中，埃默里大学的Michael C. Heaven教授和他的研究小组正在研究由碱土金属原子形成的不寻常的化学键。碱土金属的金属键和金属间键是一个既有概念又有实际意义的课题。碱土金属形成的化学键表现出不稳定的趋势，其中含有铍元素的分子表现出最不可预测的行为。由于其毒性，Be的化学性质尚未得到充分研究，但其化合物表现出独特而有价值的性质。例如，铍合金由于其特殊的强度与重量比而被用作轻质结构材料。这种金属的显著耐久性反映在它被用作极高温聚变反应堆的等离子体表面材料这一事实上。一种常见的化学键被称为共价单键，其中两个电子由两个原子共享，这对电子中的每个原子通常为键贡献一个电子。铍原子的不寻常之处在于，它们经常形成所谓的对置共价键，即两个键的电子都是由另一个原子提供的。Heaven教授和他的研究小组使用专门的仪器来表征含有碱土金属的小分子的结构和性质，包括与另一种称为碱金属的原子的键。该研究项目提供了对化学键的新见解，包括可用于测试描述键合的新理论的数据，并有助于预测用于技术应用的新化合物的性质。被研究的分子包括被提议作为量子信息存储和量子计算的基本单位（称为量子比特）的双原子。参与该项目的研究生在实验化学和理论化学方面都接受了高级培训。来自亚特兰大大学中心联盟（AUCC）机构的本科生也参与了该项目，为来自传统黑人学院和大学（HBCUs）的本科生提供研究机会。本科研究人员接受与键合机制调查相关的技术培训，并培养重要的职业技能，如网络、手稿准备和研究成果的口头陈述。目前，缺乏评价含铍和较重碱土金属化合物的高能级量子化学模型所需的实验数据。这种验证对于建立用于识别具有有价值的物理和化学性质的化合物的计算方法的信心是必要的。原型化合物的实验研究是本研究的主要目标。光谱技术，包括激光诱导荧光（LIF）和脉冲场电离零电子动能（PFI-ZEKE）测量，正被应用于气相分子和离子，以获得结构和热力学性质。被检测的物质包括LiBeLi，它被预测有一个3中心4电子键；Li4Be2，它的Be2亚基被认为有两个sigma键，没有pi键的贡献；Li6Be2，量子计算预测了一个前所未有的Be-Be三键。除了实验光谱工作外，该项目还采用了利用完全主动空间自洽场（CASSCF）和多参考构型相互作用（MRCI）方法的计算研究。该研究为研究生、本科生和博士后研究生提供了实验和理论方法方面的高级培训。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

In this project, supported by the Chemical Structure, Dynamics and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Professor Michael C. Heaven and his research group at Emory University are investigating the unusual chemical bonds formed by atoms called alkaline earth metals. Metallic and intermetallic bonding of the alkaline-earth metals is a subject of both conceptual and practical importance. The bonds formed by alkaline earth metals show erratic trends, with the most unpredictable behavior exhibited by molecules that contain the element beryllium (Be). The chemistry of Be is under-explored owing to its toxicity, but its compounds exhibit unique and valuable properties. For example, beryllium alloys are used as lightweight structural materials due to their exceptional strength to weight ratios. The remarkable durability of the metal is reflected by the fact that it is used as a plasma-facing material in extremely high-temperature fusion reactors. A common type of chemical bond is called a covalent single bond, where two electrons are shared by two atoms, each atom of the pair typically contributing one electron to the bond. Beryllium atoms are unusual in that they often form what are called dative covalent bonds, where both bonding electrons are provided by the other atom. Professor Heaven and his research group use specialized instrumentation to characterize the structure and properties of small molecules containing alkaline earth metals, including bonds with another type of atom called alkali metals. This research project provides new insights into chemical bonding in general, including data that can be used to test new theories to describe bonding and to help in the prediction of the properties of novel compounds for technological applications. The molecules under examination include diatomics that have been proposed as the basic units (called qubits) for quantum information storage and quantum computing. The graduate students engaged in this project receive advanced training in both experimental and theoretical chemistry. Undergraduate students from institutions in the Atlanta University Center Consortium (AUCC) are also involved in the project, providing research opportunities for undergraduate students from historically Black colleges and universities (HBCUs). Undergraduate researchers receive technical training related to the investigation of bonding mechanisms, and also develop important career skills, such as networking, manuscript preparation, and oral presentation of research results.At present, the experimental data needed to evaluate high-level quantum chemical models for compounds containing beryllium and the heavier alkaline earth metals are lacking. This validation is necessary to establish confidence in the computational methods that are used to identify compounds with valuable physical and chemical properties. Experimental studies of prototypical compounds are the primary objectives of this research. Spectroscopic techniques, including laser-induced fluorescence (LIF) and pulsed-field ionization-zero electron kinetic energy (PFI-ZEKE) measurements, are being applied to gas-phase molecules and ions to obtain structural and thermodynamic properties. The species being examined include LiBeLi, which is predicted to have a 3-center 4-electron bond, Li4Be2, where the Be2 sub-unit is thought to have two sigma-bonds with no pi-bonding contribution, and Li6Be2 where quantum calculations predict an unprecedented Be-Be triple bond. In addition to the experimental spectroscopic work, this project employs computational studies that utilize complete active space self-consistent field (CASSCF) and multi-reference configuration interaction (MRCI) methods. The research provides graduate, undergraduate, and post-doctoral research students with advanced training in experimental and theoretical methods.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.