Bonding of isovalent homologous actinide and lanthanide pairs with chalcogenide donors: Effect of metal f-orbital participation and donor softness

Abstract

Chemistry of f-element gains importance in several fields due to the extensive scope of their applications. The aim of this study is to understand the subtle differences in bonding of theexceptionally similar actinides and their homologous (isovalent) lanthanides with several donors, which may lead to their covalency mediated separation. Several experimental and theoretical studies have been reported to address this aspect. However, to the best of our knowledge, systematic study on the variations in the bonding patterns of the isovalent ‘Ln’ and ‘An’ pairs encompassing the effect of valence f-orbitals participation was not encountered. In this study, the minute differences in covalent interactions of these isovalent f-element pairs with chalcogenide ions of varying softness via the metal (n-2)f orbital participation was probed using relativistic density functional theory (DFT). The f-electronic configurations of the metal ions were observed to play an important role in the f-orbital participation. f0, f7 (half filled) [AnX]+/ [LnX]+ pairs expresses resistance to f-orbital directed bonding, unlike the f3, f5, f6 pairs. QTAIM study indicated that the f-orbital directed covalent bonding is pronounced for the [AnX]+ systems of the latter set than the corresponding [LnX]+s, and it is near degeneracy driven. The extent of near degeneracy driven covalency was found to increase with the subsequent increase in the softness of the donor centres i.e. oxides through sulphides to selenides, although energetic stabilisation was not rendered. These results are anticipated to provide deeper understanding on exclusive differences in bonding of the homologous An3+/Ln3+ ions with the chalcogenide donors.