₁₀₂ No ²⁺ as a soft metal ion: Extraction of ²⁵⁵ No using crown ethers

The chemical properties of transfermium elements 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, No ²⁺ exhibits similar behavior to alkaline earth metal ions, particularly Ca ²⁺ and Sr ²⁺ , suggesting hard-acid character. In this study, the soft metal ion behavior of No ²⁺ was demonstrated through complex with crown ethers. In the solid–liquid extraction of ²⁵⁵ No using di- ^t Bu-dicyclohexano-18-crown-6 in HNO ₃ , No ²⁺ was extracted as much as Sr ²⁺ . Density functional theory calculations confirmed higher stability of the No ²⁺ –DtBuCH18C6 complex, with covalent bonding involving the 6 d orbitals. Theoretical studies also revealed strong relativistic effects on the atomic orbitals of No ²⁺ , rendering No ²⁺ a soft ion similar to Pb ²⁺ .