## Abstract

Measurements are reported for sequential clustering of CH_{4} to Fe^{+} and Ni^{+} ions under equilibrium conditions. Detailed density functional theory calculations were performed to provide structural and electronic configuration information and to help analyse and interpret the experimental data. The calculations indicate that the first two CH_{4} ligands add on opposite sides of the Fe^{+} core ion in an η^{3} configuration, in an η^{2} configuration for Ni^{+}, and induce significant s/d hybridization on both of the metal centers. This hybridization both reduces Pauli repulsion and fosters sigma donation from the ligands into the 4s orbital on M^{+}. Another major covalent interaction is the donation from CH_{4} into the singly occupied d orbital(s) on M^{+} for both η^{2} and η^{3} configurations. For Fe^{+}, the change of spin state, from ^{6}D (3d^{6}4s^{1}) to ^{4}F (3d^{7}), takes place during the clustering of the first methane ligand. The clustering of the third CH_{4} to Fe^{+} and Ni^{+}, unlike Co^{+}(CH_{4})_{3}, is not impeded by the s/d hybridization present for n=1 and 2. The interactions of all three CH_{4} ligands with the Fe^{+} and Ni^{+} core are essentially the same. The m/z 120 peak [nominally Fe^{+}(CH_{4})_{4}] and the m/z 122 peak [nominally Ni^{+}(CH_{4})_{4}] were formed irreversible in the temperature range from 270 to 170 K, probably due to the persistent impurity we reported earlier for the Co^{+} system. The n=5 and 6 ligands are very weakly bound and begin a second solvation shell. Calculations suggest the n=6 cluster forms a pseudo octahedral complex.

Original language | English |
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Pages (from-to) | 265-281 |

Number of pages | 17 |

Journal | International Journal of Mass Spectrometry |

Volume | 210-211 |

DOIs | |

State | Published - Sep 14 2001 |

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_{n}

^{+}and Ni(CH

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_{n}

^{+}clusters: Experimental and theoretical bond energies for n=1-6'. Together they form a unique fingerprint.