Abstract
Californium (Cf) is currently the heaviest element accessible above microgram quantities. Cf isotopes impose severe experimental challenges due to their scarcity and radiological hazards. Consequently, chemical secrets ranging from the accessibility of 5f/6d valence orbitals to engage in bonding, the role of spin–orbit coupling in electronic structure, and reactivity patterns compared to other f elements, remain locked. Organometallic molecules were foundational in elucidating periodicity and bonding trends across the periodic table1–3, with a twenty-first-century renaissance of organometallic thorium (Th) through plutonium (Pu) chemistry4–12, and to a smaller extent americium (Am)13, transforming chemical understanding. Yet, analogous curium (Cm) to Cf chemistry has lain dormant since the 1970s. Here, we revive air-/moisture-sensitive Cf chemistry through the synthesis and characterization of [Cf(C5Me4H)2Cl2K(OEt2)]n from two milligrams of 249Cf. This bent metallocene motif, not previously structurally authenticated beyond uranium (U)14,15, contains the first crystallographically characterized Cf–C bond. Analysis suggests the Cf–C bond is largely ionic with a small covalent contribution. Lowered Cf 5f orbital energy versus dysprosium (Dy) 4f in the colourless, isoelectronic and isostructural [Dy(C5Me4H)2Cl2K(OEt2)]n results in an orange Cf compound, contrasting with the light-green colour typically associated with Cf compounds16–22.
| Original language | English |
|---|---|
| Pages (from-to) | 421-424 |
| Number of pages | 4 |
| Journal | Nature |
| Volume | 599 |
| Issue number | 7885 |
| DOIs | |
| State | Published - Nov 18 2021 |
| Externally published | Yes |
Funding
Acknowledgements We thank I. May at Los Alamos National Laboratory (LANL) and G. P. Horne at Idaho National Laboratory for discussions. We acknowledge the US Department of Energy (DOE), Office of Science (SC), Basic Energy Sciences (BES) Heavy Element Chemistry Program (HEC) at LANL (E.R.B., A.J.G., S.A.K., Z.R.J., B.L.S., F.D.W., P.Y., J.S.; DE-AC52-06NA25396), at Florida State University (T.E.A.-S., A.N.G., J.M.S., C.J.W.; DE-FG02-13ER16414), and at the University of California at Irvine (W.J.E., T.F.J., J.C.W.; DE-SC0004739). C.A.P.G. was sponsored by a Distinguished J. R. Oppenheimer Postdoctoral Fellowship (LANL-LDRD, 20180703PRD1). We thank LANL-LDRD (L.M.S., A.J.G.; 20190091ER) for aspects of the 241Am experimental work. Theoretical research was performed using EMSL (grid.436923.9), a DOE-SC User Facility sponsored by the Office of Biological and Environmental Research. J.S. also thanks the National Natural Science Foundation of China (22076130), and the Fundamental Research Funds for the Central Universities (20826041D4117) and start-up funds from Sichuan University. J.N.C. and J.D.A. acknowledge the DOE-SC, Isotope Development and Production for Research and Application subprogram within the Office of Nuclear Physics for 241Am sample conditioning and dispensing. J.D.A. thanks the NNSA Plutonium Sustainment Program and the National Nuclear Security Administration (NNSA) Material Recycle and Recovery for funding. We thank E. R. Birnbaum and B. L. Ortiz for procurement of 241Am through the National Isotope Development Center, purchased with LANL DOE-SC-BES-HEC funds.