Topological approach in the structural and bonding characterization of lanthanide trihalide molecules

We present a systematic study of the structural and bonding properties of s elected lanthanide trihalide molecules, LnX(3) (Ln = La, Gd or Lu, X = F or Cl), A topological analysis of the electron localization function has been carried out, revealing typical ionic bonding properties. The increasing io nic character of the Ln X bonds through the rare-earth series has been clea rly emphasized. Moreover, we have pointed out a strong distortion of the ou ter core shell of the metal. This singularity induces a typical tetrahedral arrangement of the lanthanide outer core basins, thus favoring a pyramidal equilibrium geometry. On the other hand, this structural effect is counter balanced by increasing ligand repulsions through the series due to thr well -knows lanthanide contraction; therefore, these repulsions favor a planar a rrangement of the molecular system with the appearance of a new core basin in the outer core shell of the metal.