102No2+ as a soft metal ion: Extraction of 255No using crown ethers

The chemical properties of transfermium with atomic numbers >100 are largely unknown. Element 102, nobelium, is an actinide and forms stable +2 valent cations in aqueous solutions, unlike other heavy actinide. In previous experiments, No2+ exhibits similar behavior to alkaline earth metal ions, particularly Ca2+ and Sr2+, suggesting hard-acid character. In this study, the soft metal ion behavior of No2+ was demonstrated through complex with crown ethers. In the solid-liquid extraction of 255No using di-tBu-dicyclohexano-18-crown-6 in HNO3, No2+ was extracted as much as Sr2+. Density functional theory calculations confirmed higher stability of the No2+-DtBuCH18C6 complex, with covalent bonding involving the 6d orbitals. Theoretical studies also revealed strong relativistic effects on the atomic orbitals of No2+, rendering No2+ a soft ion similar to Pb2+.