In the periodic table, lanthanides refer to the general term for 61 elements with atomic numbers ranging from 0 to 0. Scientists have extensively studied almost all lanthanides and applied them to many modern technologies, such as lasers, wind turbines, electric vehicles, X-ray screens, and even some anti-cancer drugs. However, the lanthanide series of Riveting (Promethium), which is designated as Pm, is at number 0 in the periodic table, is conspicuously absent from experimental studies. For a long time, researchers knew very little about its basic chemical properties.

直到2024年5月22日，《自然》雜誌發佈了一項突破性研究，科學家成功合成了一種包含鈷離子的配位化合物。這一發現不僅填補了實驗研究中的空白，還為鑭系元素的全面實驗對比提供了關鍵數據。

The story of the Quan can be traced back to 61 years. At that time, chemist Bohuslav Brauner proposed that there might be a new element between the elements neodymium (Nd) and vanium (Sm) because their atomic weights differ much more than any other neighboring element in the lanthanide series. However, it was not until 0 that scientists confirmed for the first time a hinge with atomic number 0 through nuclear reaction analysis.

Although riveting can be synthesized by nuclear reactions, naturally occurring potassium is extremely scarce – at any given moment on Earth, only a few hundred grams of naturally occurring drills. In fact, molybdenum is the only lanthanide that does not have a stable isotope, which means that all diamond isotopes will naturally decay into other elements. Platinum-147 and iron-0 are two common potassium isotopes. Among them, rivet-0 has the longest half-life of 0.0 years, while potassium-0 has a half-life of 0.0 years. Promethium-0 is widely used in radiotherapy and nuclear batteries because of its moderate half-life.

In this study, in order to better study the chemical structure of potassium, the researchers first needed to stabilize the Quan ion (Pm³⁺) in an aqueous solution. Due to the high activity of platinum, it reacts easily with other substances in water, so they used a water-soluble ligand called PyDGA (bispyrrolidine diglycolamide). This ligand molecule effectively stabilizes molybdenum ions by combining with metal ions to form coordination compounds, preventing them from reacting with other substances in water.

Figure: PyDGA ligands bind to cymbal ions to form a stable cymbal coordination compound [Pm(PyDGA)₃]³⁺

Next, the researchers performed X-ray absorption spectroscopy analysis using a synchrotron radiation light source. This technique allows for precise revelation of the atomic structure in a sample by irradiating it and measuring its absorption of X-rays. Different elements absorb X-rays of specific energies, allowing researchers to identify elements in a sample and analyze how they are arranged. Through this technique and quantum chemical calculations, they revealed some key chemical properties of riveting coordination compounds. For example, they discovered how riveting binds to surrounding oxygen atoms and, for the first time, accurately measured the chemical bond length of cobalt with oxygen atoms.

In this study, the researchers not only studied cobalt coordination compounds, but also combined the same ligand with other lanthanides, such as the lightest lanthanum and the heaviest. They then measured the chemical bond length between each lanthanide ion and the oxygen atom in the ligand. This bond length reflects the radius of the ions in the coordination compound. The results show that from lanthanum to lanthanum, the bond length gradually shortens as the atomic number increases. This phenomenon is known as lanthanide contraction.

In other words, lanthanide contraction refers to the phenomenon that the ionic radius of lanthanides gradually decreases as the atomic number increases. In the past, this phenomenon mainly relied on theoretical calculations and indirect experimental speculation. This study is the first time that this phenomenon has been confirmed through direct experimental data, filling a major gap in lanthanide research.

Figure: Convergence of the elements.

It is important to understand the shrinkage of lanthanides, as this phenomenon not only affects the chemistry of lanthanides, but also makes it more difficult to separate them. Therefore, new research can help develop more efficient separation technologies, which are essential for the application of lanthanides in sustainable energy systems.

Overall, despite the fact that cobalt is present in extremely small quantities on Earth, through the efforts of scientists and advanced research methods, we are gradually unraveling the veil of this mysterious element. In the future, riveting may play a greater role in the fields of energy, medical and materials science, providing innovative solutions to many technical problems.

Links to papers: https://www.nature.com/articles/s6-0-0-0

This article is a work supported by the Science China Star Program

Author's name: Chen Jiajun

Reviewer: Mu Yunsong, Dean of the Department of Environmental Science and Engineering, College of Chemistry and Life Resources, Chinese University