How can f-block mono-cations behave as Mono-Cations of d-block transition metals ?

International audienceThe electronic structures of LnNH+ is studied by DFT (B3LYP) quantum calculation for the Ln = La, Eu and Gd 4f-block elements (lanthanides). Ln ≡N triple bonds of essentially d-character are formed for La and Gd explaining why La+ and Gd+ behave like d-block elements as experimentally evidenced by mass spectrometry, and why the Ln+ reactivity is correlated with its electron-promotion energy: the present theoretical study is a support to such correlation and qualitative knowledge. The Ln+ + NH3 → LnNH 3+ → transition state → HLn=NH 2+ → transition state → Ln≡NH+ + H2 reaction pathway is calculated. The formation of HLn=NH2+ corresponds to the formation of new covalent bonds associated with more electron pairing, and corresponding lowering of the spin multiplicity-spin crossing reaction. It is in this step that low electron-promotion energy is required to promote an Ln 4f electron onto an Ln 5d orbital as typically for La+ and Gd+. Similar geometry, bonding and electronic cofiguration are calculated for NpNH +-an actinide complex observed by mass spectrometry-with higher participation of 5f-valence orbitals (20% and 25% for the σ and π bonds) as compared to the 4f-valence orbitals (3% and 8%) of GdNH+ : Gd+ and Np+ are the only lanthanide and actinide cations with two non-f-valence electrons-one s and one din their ground states