A TANDEM MASS-SPECTROMETRY AND FOURIER-TRANSFORM ION-CYCLOTRON RESONANCE (FT-ICR) STUDY OF RMN(-ETHER) COMPLEXES IN THE GAS-PHASE()(CROWN)

Two ion-molecule 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 st able RMn(+)(3n-crown-n) (n = 4,5,6) ions, Ligand substitution at the M n atom took place when it was sterically accessible to the incoming ma crocyclic molecule, The efficiency of the macrocyclic ligand exchange was also greatly affected by the coordinative vacancies occupied by th e group R, The 5-coordinative C5H5-ligand completely prevented metal a tom attack by a second macrocyclic molecule, Very slow ligand substitu tion was observed for (acac)(2)Mn+(3n-crown-n) and (acac)Mn+(3n-crown- n) ions (n = 4,5), Whenever ligand substitution occurred, it always in volved 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 m olecules (C2H4O, RH, RH + C2H2), These fragmentations were attributed to the metal atom retaining its stable oxidative state Mn(2+). The ste p-wise loss of C2H4O molecules resulted in contraction of the macrocyc lic ring and the formation of a smaller crown ether in the coordinatio n sphere of the metal atom.