Researchers created rare complexes with uranium and nickel atoms that feature multiple uranium-nickel single bonds (Nat. Chem. 2019, DOI: 10.1038/s41557-018-0195-4). Congqing Zhu of Nanjing University and colleagues chelated heptadentate ligands containing nitrogen and phosphorus with uranium atoms. Then they added a nickel reagent, which formed bridges between the uranium-ligand complexes. Uranium chemistry expert Suzanne C. Bart of Purdue University said the researchers drew on decades of research to design the ligands that make these unusual complexes possible. Zhu says the complexes are stabler than the two previously reported compounds with multiple uranium-metal bonds. Two of the group’s complexes contain four U-Ni bonds, and a third has six. The researchers say density functional theory calculations by coauthor Laurent Maron of Paul Sabatier University suggest uranium atoms in two of the complexes have a 5f26d1 electron configuration rather than the expected 5f36d⁰ configuration, a result of the U-Ni bonds’ partly ionic character.