Developing Magnetic and Metallic Behavior in High-Nuclearity Nickel Cluster Carbonyls. A LCGTO-LDF Study of [Ni₉(CO)₁₈]^n--, [Ni₁₀Ge(CO)₂₀]^n-, [Ni₃₂C₆(CO)₃₆]^n-, and [Ni₄₄(CO)₄₈]^n- Compounds

We have performed all-electron calculations on the electronic structure of medium-and high-nuclearity bare and carbonylated nickel cluster compounds by means of the linear combination of Gaussian type orbitals (LCGTO) local density functional (LDF) method. The transition from the molecular state to the metallic state as a function of the cluster size was studied by determining the one-electron energy spectra and the magnetic properties of naked and ligated Ni clusters. Medium-size clusters like [Ni₉(CO)₁₈]^2- and [Ni₁₀Ge(CO)₂₀]^2-, where all the Ni atoms are on the surface of the metal cage, show typically molecular features. They do not exhibit any magnetic behavior, and their one-electron spectrum has a discrete nature near the cluster HOMO with a well-defined HOMO-LUMO gap. By contrast, both high-nuclearity clusters, [Ni₃₂C₆(CO)₃₆]^n- and [Ni₄₄(CO)₄₈]^n-, show typical signs of a developing metallic character in agreement with experimental magnetic measurements. In particular, a magnetic behavior connected with the high density of states near the Fermi level is observed. This is entirely connected to the presence of Ni atoms in the interior (“bulk”) of the metal cage. The role of the CO ligands and of interstitial atoms, like C or Ge, in quenching the magnetic moment of the bare cluster is elucidated.