title: Collision-induced gas-phase reactions of perhalogenated closo-dodecaborate clusters--a comparative study.
abstract: The gas phase reactivity of perhalogenated closo-dodecaborate clusters [B(12)X(12)](2-) (X = F, Cl, Br, I) with N-tetraalkylated ammonium counter ions was investigated by electrospray ionization ion trap mass spectrometry (ESI-IT-MS). Collisions with the background gases introduced a broad variety of gas phase reactions. This study represents the first experimental approach to a new class of boron-rich boron clusters that are not accessible in the condensed phase. The anionic ion pair [B(12)X(12) + N(C(n)H(2n+1))(4)](-) is generally found as the ion of highest mass. Its reaction sequence starts with an alkyl transfer from the ammonium ion to the dodecaborate cluster. Subsequently, the alkylated intermediate [B(12)X(12) + C(n)H(2n+1)](-) decomposes to give very reactive ions of the general formula [B(12)X(11)](-). These ions possess a free boron vertex and immediately bind to the residual gases N(2) and H(2)O in the ion trap by formation of the corresponding adducts [B(12)X(11) + N(2)](-) and [B(12)X(11) + H(2)O](-). Subsequent fragmentations of the water adduct repetitively substitute halogen atoms by hydroxyl groups. The fragmentation process of the free anion [B(12)X(12)](2-) depends on the applied excitation energy and on the halogen substituent X. A radical dehalogenation of the B(12) unit is observed for X = I, whereas for X = Cl or F the loss of small molecules (mainly BX(3)) dominates. The different reaction behavior is explained by the different electron affinity of the halogens and the strength of the boron-halogen-bonds. Surprisingly, isolation of the fragment ion [B(12)I(9)](-) in the ion trap yields the highly stable [B(24)I(18)](2-) dianion. This observation suggests a reaction between two negative ions in the gas phase.
authors.affiliation: Fachbereich 2 (Chemie/Biologie), Universität Bremen, Bremen, Germany.
authors.forename: Jonas
authors.initials: J
authors.lastname: Warneke
authors.forename: Thomas
authors.initials: T
authors.lastname: Dülcks
authors.forename: Carsten
authors.initials: C
authors.lastname: Knapp
authors.forename: Detlef
authors.initials: D
authors.lastname: Gabel
mesh_terms: D001881:Borates / Q000737:chemistry*; D005740:Gases; D006219:Halogens / Q000737:chemistry*; D015394:Molecular Structure; D044367:Phase Transition; D011789:Quantum Theory; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D001881:Borates; D005740:Gases; D006219:Halogens