Berkelocene’s “sandwich” structure: a berkelium atom (purple) between two substituted cyclooctatetraene rings (gray). Periodic Table background highlights rare-earths (pink) and actinides (blue). Credit: Alyssa Gaiser/LBNL.
Scientists at Lawrence Berkeley National Laboratory built a first: berkelocene. It binds carbon to berkelium-249 and puts the atom between two substituted cyclooctatetraene-based ligands. The surprise? In this molecule, berkelium is tetravalent (Bk⁴⁺), not Tb-like as many models predicted. In plain terms: the berkelium atom ends up more positively charged than expected and bonds to the carbon rings in an unusual way.
The team had just 0.3 mg of berkelium from ORNL’s National Isotope Development Center. They worked in air-free, radiological labs and confirmed the symmetric “sandwich” by single-crystal X-ray diffraction; the work used resources at the Advanced Light Source. Computations at the University at Buffalo and spectroscopy show Bk–C bonding and charge distribution that depart from lanthanide analogies. Those details sharpen actinide models. They are useful for problems like long-term nuclear-waste chemistry.
This finding overturns decades-old theories on actinide chemistry, especially for transplutonium elements like berkelium, and could improve strategies for nuclear waste management and remediation.
The work was published in Science (DOI: 10.1126/science.adr3346).
Berkelium, a synthetic radioactive element with atomic number 97, belongs to the actinide series and does not occur naturally on Earth. Discovered in December 1949 at the University of California, Berkeley, by chemists Stanley G. Thompson, Albert Ghiorso and Glenn T. Seaborg, it was named after the city and produced via nuclear reactions in accelerators or reactors. As one of the transuranic elements beyond uranium, berkelium exists only in trace amounts. In other words, typically milligrams or less, limiting its study to specialized labs handling high radioactivity.
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