Fe(CH4)(n)(+) and Ni(CH4)(n)(+) clusters: experimental and theoretical bond energies for n=1-6

Measurements are reported for sequential clustering of CH4 to Fe+ and Ni+ i ons under equilibrium conditions. Detailed density functional theory calcul ations were performed to provide structural and electronic configuration in formation and to help analyse and interpret the experimental data. The calc ulations indicate that the first two CH, ligands add on opposite sides of t he Fe+ core ion in an eta (3) configuration, in an eta (2) configuration fo r Ni+, and induce significant s/d hybridization on both of the metal center s. This hybridization both reduces Pauli repulsion and fosters sigma donati on from the ligands into the 4s orbital on M+. Another major covalent inter action is the donation from CH4 into the singly occupied d orbital(s) on M for both eta (2) and eta (3) configurations. For Fe+ the change of spin st ate, from D-6 (3d(6)4s(1)) to F-4 (3d(7)), takes place during the clusterin g of the first methane ligand. The clustering of the third CH4 to Fe+ and N i+, unlike Co+(CH4)(3), is not impeded by the s/d hybridization present for n = 1 and 2. The interactions of all three CH4 ligands, with the Fe+ and N i+ core are essentially the same. The m/z 120 peak [nominally Fe+(CH4)(4)] and the m/z 122 peak [nominally Ni+(CH4)(4)] were formed irreversible in th e temperature range from 270 to 170 K, probably due to the persistent impur ity we reported earlier for the Co+ system. The n = 5 and 6 ligands are ver y weakly bound and begin a second solvation shell. Calculations suggest the n = 6 cluster forms a pseudo octahedral complex. (C) 2001 Elsevier Science B.V.