## Abstract

Measurements are reported for sequential clustering of CH_{4} to Co^{+} ions under equilibrium conditions. The CH_{4} cluster bond strengths show a pairwise behavior: -ΔH_{0}/^{0} = 23.1 and 25.3 kcal/mol for n = 1 and 2; 7.3 and 5.2 kcal/mol for n = 3 and 4; and ∼2 kcal/mol for both n = 5 and 6. This pairwise behavior is well reproduced by large basis set density functional theory calculations. These calculations indicate n = 1 and n = 2 add on opposite sides of the Co^{+} ion in η^{2} configuration and induce significant s/d hybridization on Co^{+}. This hybridization both reduces Pauli repulsion and fosters sigma donation into the 4s orbital on Co^{+}. Clusters n = 3 and n = 4 add at 90° to the n = 1 and 2 line of centers forming a planar system. The s/d hybridization is unfavorable for these clusters resulting in longer Co^{+}-C bond lengths and substantially reduced binding energies. To n = 5 and 6 ligands probably complete a pseudo octahedral complex and are very weakly bound, perhaps defining a second solvation shell. An impurity contributed substantially to the experimental peak at m/z = 123 corresponding to Co^{+}(CH_{4})_{4}. The impurity was tentatively identified as O_{2}Co^{+}(CH_{4})_{2} and experimental protocals were developed to eliminate its impact on the data reported here. It is suggested this impurity could be responsible for published guided ion beam results that found a substantially larger binding energy for n = 4 than for n = 3 in contrast to what is reported here.

Original language | English |
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Pages (from-to) | 281-294 |

Number of pages | 14 |

Journal | International Journal of Mass Spectrometry |

Volume | 204 |

Issue number | 1-3 |

DOIs | |

State | Published - Feb 6 2001 |

## Keywords

- Cobalt
- Density function theory
- Methane
- Sigma bond activation
- Transition metal

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