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Scientists Determine Properties of Extremely Rare Element: Promethium
Scientists Determine Properties of Extremely Rare Element: Promethium
May 22, 2024 by News Staff
Promethium is extremely rare, with only about 0.5 kg naturally occurring in Earth’s crust at any given time.
Conceptual art shows the rare earth element promethium in a vial surrounded by an organic ligand. Image credit: Jacqueline DeMink / Thomas Dyke / ORNL.
Discovered in 1945 at Clinton Laboratories, promethium is a lanthanide element with symbol Pm and atomic number 61.
[...]
Some of its properties have remained elusive despite the rare earth element’s use in medical studies and long-lived nuclear batteries.
[...]
The researchers bound, or chelated, radioactive promethium with special organic molecules called diglycolamide ligands.
Then, using X-ray spectroscopy, they determined the properties of the complex, including the length of the promethium chemical bond with neighboring atoms — a first for science and a longstanding missing piece to the periodic table of elements.
[...]
May 22, 2024 by News Staff
Promethium is extremely rare, with only about 0.5 kg naturally occurring in Earth’s crust at any given time.
Conceptual art shows the rare earth element promethium in a vial surrounded by an organic ligand. Image credit: Jacqueline DeMink / Thomas Dyke / ORNL.
Discovered in 1945 at Clinton Laboratories, promethium is a lanthanide element with symbol Pm and atomic number 61.
[...]
Some of its properties have remained elusive despite the rare earth element’s use in medical studies and long-lived nuclear batteries.
[...]
The researchers bound, or chelated, radioactive promethium with special organic molecules called diglycolamide ligands.
Then, using X-ray spectroscopy, they determined the properties of the complex, including the length of the promethium chemical bond with neighboring atoms — a first for science and a longstanding missing piece to the periodic table of elements.
[...]
================
https://www.nature.com/articles/s41586-024-07267-6
(links, full text, pdf available at source link)
Article Open access
Published: 22 May 2024
Observation of a promethium complex in solution
Darren M. Driscoll, Frankie D. White, Subhamay Pramanik, Jeffrey D. Einkauf, Bruce Ravel, Dmytro Bykov, Santanu Roy, Richard T. Mayes, Lætitia H. Delmau, Samantha K. Cary, Thomas Dyke, April Miller, Matt Silveira, Shelley M. VanCleve, Sandra M. Davern, Santa Jansone-Popova, Ilja Popovs & Alexander S. Ivanov
Nature volume 629, pages 819–823 (2024) Cite this article
Metrics
Abstract
Lanthanide rare-earth metals are ubiquitous in modern technologies1,2,3,4,5, but we know little about chemistry of the 61st element, promethium (Pm)6, a lanthanide that is highly radioactive and inaccessible. Despite its importance7,8, Pm has been conspicuously absent from the experimental studies of lanthanides, impeding our full comprehension of the so-called lanthanide contraction phenomenon: a fundamental aspect of the periodic table that is quoted in general chemistry textbooks. Here we demonstrate a stable chelation of the 147Pm radionuclide (half-life of 2.62 years) in aqueous solution by the newly synthesized organic diglycolamide ligand. The resulting homoleptic PmIII complex is studied using synchrotron X-ray absorption spectroscopy and quantum chemical calculations to establish the coordination structure and a bond distance of promethium. These fundamental insights allow a complete structural investigation of a full set of isostructural lanthanide complexes, ultimately capturing the lanthanide contraction in solution solely on the basis of experimental observations. Our results show accelerated shortening of bonds at the beginning of the lanthanide series, which can be correlated to the separation trends shown by diglycolamides9,10,11. The characterization of the radioactive PmIII complex in an aqueous environment deepens our understanding of intra-lanthanide behaviour12,13,14,15 and the chemistry and separation of the f-block elements16.
Main
One reason promethium (Pm) was so elusive for many years, despite a relatively low atomic number, is that it is the only element in the lanthanide (Ln) series (elements with atomic numbers 57–71) with no stable isotopes. Nowadays, mostly synthetic radioisotope 147Pm (with half-life τ1/2 = 2.62 years) is produced and isolated in small quantities through nuclear fission in reactors and subsequent tedious purification steps for many applications. Promethium uses range from long-life nuclear batteries used in space craft to radiation therapy7,8. A key obstacle impeding the efficient recovery of this critical element resides in our limited comprehension of the Pm coordination chemistry. In contrast to other lanthanides that favour the +3 oxidation state under ambient conditions, even the most fundamental characteristics of Pm in aqueous solution, including the bond distances and coordination number, remain unexplored. This valuable information is exceptionally challenging to obtain due to its radioactivity, synthetic nature and lack of availability. Only a few simple inorganic PmIII solids, such as halides17, oxide18, oxalate19, molybdate and tungstate20 have been prepared and characterized by X-ray powder diffraction to determine the lattice parameters. Furthermore, the absorption bands in the visible spectrum17,21,22, Raman spectra23 and magnetic susceptibility24 of the PmIII oxide and halides were reported. Beyond these examples, the fundamental chemistry of Pm is virtually unknown, and there are no experimental data to benchmark theoretical models for predicting Pm chemical bonding, structure and reactivity in solution. In addition, it is well known that the gradual population of the 4f electron shell in conjunction with relativistic effects cause a continuous decrease in the size of the ionic radii along the lanthanide series, leading to structural changes in Ln complexes. Whereas this lanthanide contraction phenomenon taught in general chemistry textbooks has been inferred mostly from theory25,26,27,28,29 and Shannon’s effective ionic radii database30, it still lacks experimental structural evidence for a complete set of lanthanides in solution that includes radioactive Pm31,32,33,34,35,36. Advancing our fundamental knowledge in this field is critical for rationalizing and predicting the structurally diverse coordination chemistry shown by lanthanides1,3,12.
[...]
Published: 22 May 2024
Observation of a promethium complex in solution
Darren M. Driscoll, Frankie D. White, Subhamay Pramanik, Jeffrey D. Einkauf, Bruce Ravel, Dmytro Bykov, Santanu Roy, Richard T. Mayes, Lætitia H. Delmau, Samantha K. Cary, Thomas Dyke, April Miller, Matt Silveira, Shelley M. VanCleve, Sandra M. Davern, Santa Jansone-Popova, Ilja Popovs & Alexander S. Ivanov
Nature volume 629, pages 819–823 (2024) Cite this article
Metrics
Abstract
Lanthanide rare-earth metals are ubiquitous in modern technologies1,2,3,4,5, but we know little about chemistry of the 61st element, promethium (Pm)6, a lanthanide that is highly radioactive and inaccessible. Despite its importance7,8, Pm has been conspicuously absent from the experimental studies of lanthanides, impeding our full comprehension of the so-called lanthanide contraction phenomenon: a fundamental aspect of the periodic table that is quoted in general chemistry textbooks. Here we demonstrate a stable chelation of the 147Pm radionuclide (half-life of 2.62 years) in aqueous solution by the newly synthesized organic diglycolamide ligand. The resulting homoleptic PmIII complex is studied using synchrotron X-ray absorption spectroscopy and quantum chemical calculations to establish the coordination structure and a bond distance of promethium. These fundamental insights allow a complete structural investigation of a full set of isostructural lanthanide complexes, ultimately capturing the lanthanide contraction in solution solely on the basis of experimental observations. Our results show accelerated shortening of bonds at the beginning of the lanthanide series, which can be correlated to the separation trends shown by diglycolamides9,10,11. The characterization of the radioactive PmIII complex in an aqueous environment deepens our understanding of intra-lanthanide behaviour12,13,14,15 and the chemistry and separation of the f-block elements16.
Main
One reason promethium (Pm) was so elusive for many years, despite a relatively low atomic number, is that it is the only element in the lanthanide (Ln) series (elements with atomic numbers 57–71) with no stable isotopes. Nowadays, mostly synthetic radioisotope 147Pm (with half-life τ1/2 = 2.62 years) is produced and isolated in small quantities through nuclear fission in reactors and subsequent tedious purification steps for many applications. Promethium uses range from long-life nuclear batteries used in space craft to radiation therapy7,8. A key obstacle impeding the efficient recovery of this critical element resides in our limited comprehension of the Pm coordination chemistry. In contrast to other lanthanides that favour the +3 oxidation state under ambient conditions, even the most fundamental characteristics of Pm in aqueous solution, including the bond distances and coordination number, remain unexplored. This valuable information is exceptionally challenging to obtain due to its radioactivity, synthetic nature and lack of availability. Only a few simple inorganic PmIII solids, such as halides17, oxide18, oxalate19, molybdate and tungstate20 have been prepared and characterized by X-ray powder diffraction to determine the lattice parameters. Furthermore, the absorption bands in the visible spectrum17,21,22, Raman spectra23 and magnetic susceptibility24 of the PmIII oxide and halides were reported. Beyond these examples, the fundamental chemistry of Pm is virtually unknown, and there are no experimental data to benchmark theoretical models for predicting Pm chemical bonding, structure and reactivity in solution. In addition, it is well known that the gradual population of the 4f electron shell in conjunction with relativistic effects cause a continuous decrease in the size of the ionic radii along the lanthanide series, leading to structural changes in Ln complexes. Whereas this lanthanide contraction phenomenon taught in general chemistry textbooks has been inferred mostly from theory25,26,27,28,29 and Shannon’s effective ionic radii database30, it still lacks experimental structural evidence for a complete set of lanthanides in solution that includes radioactive Pm31,32,33,34,35,36. Advancing our fundamental knowledge in this field is critical for rationalizing and predicting the structurally diverse coordination chemistry shown by lanthanides1,3,12.
[...]