Californium complex offers bonding insights

Abstract

A californium complex has provided the first crystal structure featuring a californium-carbon bond, helping probe bonding trends in the nether regions of the periodic table ( Nature 2021, DOI: 10.1038/s41586-021-04027-8 ). Californium is the heaviest element available in milligram quantities. Its scarcity and radioactivity pose huge experimental challenges. “We’re really pushing the limits of the smallest scale at which you can do classical synthetic chemistry,” says Andrew Gaunt, a researcher at Los Alamos National Laboratory and part of the team that created the complex. The researchers combined 2 mg of 249 Cf 3+ with potassium tetramethylcyclopentadienide in diethyl ether, forming crystals of a dark-orange metallocene complex (shown). Metallocenes are compounds in which aromatic ligands sandwich a metal ion. Most californium complexes are light green; the metallocene’s unusual color is likely due to an electron being excited from cyclopentadienyl to californium. X-ray crystallography revealed that the two cyclopentadienyl ligands were separated