Abstract
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+
.