Generation of Gas-Phase VO2+, VOOH+, and VO2+-Nitrile Complex Ions by Electrospray Ionization and Collision-Induced Dissociation
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- 作者：Zack Parsons ; Chris Leavitt ; Thanh Duong ; Gary S. Groenewold ; Garold L. Gresham ; Michael J. Van Stipdonk
- 刊名：Journal of Physical Chemistry A
- 出版年：2006
- 出版时间：October 19, 2006
- 年：2006
- 卷：110
- 期：41
- 页码：11627 - 11635
- 全文大小：142K
- 年卷期：v.110,no.41(October 19, 2006)
- ISSN：1520-5215
文摘
Cationic metal species normally function as Lewis acids, accepting electron density from bound electron-donating ligands, but they can be induced to function as electron donors relative to dioxygen by carefulcontrol of the oxidation state and ligand field. In this study, cationic vanadium(IV) oxohydroxy complexeswere induced to function as Lewis bases, as demonstrated by addition of O2 to an undercoordinated metalcenter. Gas-phase complex ions containing the vanadyl (VO2+), vanadyl hydroxide (VOOH+), or vanadium(V) dioxo (VO2+) cation and nitrile (acetonitrile, propionitrile, butyronitrile, or benzonitrile) ligands weregenerated by electrospray ionization (ESI) for study by multiple-stage tandem mass spectrometry. The principalspecies generated by ESI were complexes with the formula [VO(L)n]2+, where L represents the respectivenitrile ligands and n = 4 and 5. Collision-induced dissociation (CID) of [VO(L)5]2+ eliminated a single nitrileligand to produce [VO(L)4]2+. Two distinct fragmentation pathways were observed for the subsequentdissociation of [VO(L)4]2+. The first involved the elimination of a second nitrile ligand to generate [VO(L)3]2+,which then added neutral H2O via an association reaction that occurred for all undercoordinated vanadiumcomplexes. The second [UO(L)4]2+ fragmentation pathway led instead to the formation of [VOOH(L)2]+through collisions with gas-phase H2O and concomitant losses of L and [L + H]+. CID of [VOOH(L)2]+caused the elimination of a single nitrile ligand to generate [VOOH(L)]+, which rapidly added O2 (in additionto H2O) by a gas-phase association reaction. CID of [VONO3(L)2]+, generated from spray solutions createdby mixing VOSO4 and Ba(NO3)2 (and precipitation of BaSO4), caused elimination of NO2 to produce [VO2(L)2]+. CID of [VO2(L)2]+ produced elimination of a single nitrile ligand to form [VO2(L)]+, a V(V) analogueto the O2-reactive V(IV) species [VOOH(L)]+; however, this V(V) complex was unreactive with O2, whichindicates the requirement for an unpaired electron in the metal valence shell for O2 addition. In general, the[VO2(L)2]+ species required higher collisions energies to liberate the nitrile ligand, suggesting that they aremore strongly bound than the [VOOH(L)2]+ counterparts.