A tandem mass spectrometry and Fourier transform ion cyclotron resonance (FTICR) study of RMn

⁺ (crown-ether) complexes in the gas phase

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Eur. J. Mass Spectrom. 3, 27 - 36 (1997)

A tandem mass spectrometry and Fourier transform ion cyclotron resonance (FTICR) study of RMn⁺ (crown-ether) complexes in the gas phase

Dmitri V. Zagorevskii and John L. Holmes^*
Chemistry Department, University of Ottawa, Ottawa, Ontario, Canada K1N 6NS.
Clifford H. Watson and John R. Eyler
Department of Chemistry, University of Florida, PO Box 117200,Gainesville, FL 32, USA.

ABSTRACT:

Two ionmolecule reactions were identified as the source of complexes of crown ethers with RMn⁺ (R = H, Br, OH, C₆H₅,acac, C₅H₅, C₅H₄CH₃) ions in the gas phase. Adduct formation was the important route to stable RMn⁺(3n-crown-n) (n = 4,5,6) ions. Ligand substitution at the Mn atom took place when it was sterically accessible to the incoming macrocyclic molecule. The efficiency of the macrocyclic ligand exchange was also greatly affected by the coordinative vacancies occupied by the group R. The 5-coordinative C₅H₅-ligand completely prevented metal atom attack by a second macrocyclic molecule. Very slow ligand substitution was observed for (acac)₂Mn⁺(3n-crown-n) and (acac)Mn⁺(3n-crown-n) ions (n = 4,5).Whenever ligand substitution occurred, it always involved the replacement of a smaller crown ether by a larger homologue. The unimolecular dissociation of RMn⁺(3n-crown-n) ions was studied by tandem mass spectrometry; it was dominated by the loss of neutral molecules (C₂H₄O, RH, RH + C₂H₂). These fragmentations were attributed to the metal atom retaining its stable oxidative state Mn(2+). The step-wise loss of C₂H₄O molecules resulted in contraction of the macrocyclic ring and the formation of a smaller crown ether in the coordination sphere of the metal atom.

Keywords: Substituted manganese ioncrown ether complexes, mass spectrometry, reactivity.

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