The electronic structure and magnetic properties of the nickel tetramer and its partially carbonylated forms

Density functional calculations using nonlocal functionals for exchange and correlation have been carried out on Ni-4 and Ni-4(CO)(x) (x = 1, 2) species. in the case of the nonligated cluster, all the forms originated by Jahn-Teller distortion of the tetrahedron have been investigated. The lowest-energy states are all characterized by a spin multiplicity corresponding to the total spin S = 2; the four unpaired electrons are strongly localized in the atomic 3d shells. The Ni-hii bond is dominated by the s-s interaction, as is proved by changes in electron distribution caused by the ionization. The interaction of the nickel tetramer with one CO ligand has no substantial effect on magnetic properties. On the contrary, two CO groups are already sufficient, when coordinated in a mu(2) mode, to quench completely the magnetism of the cluster. The mu(2) coordination is found to be more effective in reducing the paramagnetism than the mu(3) coordination