Ammonium Counterions Research Articles

Progression of the Morphology in Random Ionomers Containing Bulky Ammonium Counterions

Poly(isoprene-ran-dimethyloctylammonium styrenesulfonate) (P(I-ran-DMOASS)) copolymers with high molecular weights and dimethyloctylammonium styrenesulfonate (DMOASS) compositions ranging between 8 and 40 mol % (30 and 77 wt %) were synthesized via nitroxide-mediated polymerization. Thermal and viscoelastic characterization revealed distinct behaviors for the low (30–51 wt %) and high (56–77 wt %) DMOASS content copolymers. Three structural regimes were identified: ion clusters (30 wt % DMOASS), continuous ionic phase (56–77 wt % DMOASS), and the coexistence of the two (42–51 wt % DMOASS). As DMOASS content increased, small-angle X-ray scattering revealed a gradual transition from the characteristic ion cluster structure to a smaller, more regular backbone–backbone structure associated with a continuous ionic phase. The ion clusters acted as physical cross-links and introduced additional elasticity into the low DMOASS content copolymer, while the continuous ionic phase showed restricted flow behavior and ...

Replacing calcium with ammonium counterion in lignosulfonates from paper mills affects their molecular properties and bioactivity

Lignosulfonates are important by-products of the paper industry and may be transformed into different commodities. We studied the molecular properties of ammonium (LS-AM) and calcium Lignosulfonates (LS-C) and evaluated their bioactivity towards the early development of maize plantlets. The FT-IR, 13C NMR and 1H-13C-HSQC-NMR spectra showed that the two lignosulfonates varied in hydroxyl, sulfonate and phenolic content, while DOSY-NMR spectroscopy suggested a similar diffusivity. High Performance Size Exclusion Chromatography (HPSEC) was used to simulate the effects of root-exuded acids and describe the conformational dynamics of both LS substrates in acidic aqueous solutions. This technique showed that LS-C was stabilized by the divalent Ca2+ counterion, thus showing a greater conformational stability than LS-AM, whose components could not be as efficiently aggregated by the monovalent NH4+ counter-ion. The plant bioassays revealed that LS-AM enhanced the elongation of the root system, whereas LS-C significantly increased both total and shoot plant weights. We concluded that the lignosulfonate bioactivity on plant growth depended on the applied concentrations, their molecular properties and conformational stability.

Counterion-Regulated Dynamics of Water Confined in Lyotropic Liquid Crystalline Morphologies.

The dynamics of confined water is of fundamental and long-standing interest. In technologically important forms of confinement, such as proton-exchange membranes, electrostatic interactions with the confining matrix and counterions play significant roles on the properties of water. There has been recent interest on the dynamics of water confined to the lyotropic liquid crystalline (LLC) morphologies of Gemini dicarboxylate surfactants. These systems are exciting because the nature of confinement, for example, size and curvature of channels and surface functionality is dictated by the chemistry of the self-assembling surfactant molecules. Quasielastic neutron scattering experiments have shown an interesting dependence of the water self-diffusion constant, Dα, on the identity (denoted α) of the counterion: at high hydration, the magnitude of the water self-diffusion constant is in the order DTMA < DNa < DK, where TMA, Na, and K refer to tetramethyl ammonium, sodium, and potassium counterions, respectively. This sequence is similar to what is seen in bulk electrolyte solutions. At low hydrations, however, the order of water self-diffusion is different, that is, DNa < DTMA < DK. In this work, we present molecular dynamics simulations for the dynamics of water in the LLC phases of dicarboxylate Gemini surfactants. The simulations reproduce the trends seen in experiments. From an analysis of the trajectories, we hypothesize that two competing factors play a role: the volume accessible to the water molecules and the correlations between the water and the counterion. The excluded volume effect is the largest with TMA+, and the electrostatic correlation is the strongest with Na+. The observed trend is a result of which of these two effects is dominant at a given water to surfactant ratio.

The effect of cation chemistry on physicochemical behaviour of superconcentrated NaFSI based ionic liquid electrolytes and the implications for Na battery performance

There is growing interest in ionic liquid based electrolytes for Na metal and Na-ion batteries. Here we compare three quite distinct bis(fluorosulfonyl)imide (FSI) anion based ionic liquids with small alkyl phosphonium (trimethyl isobutyl phosphonium, methyl tri-isobutyl: P111i4, P1i4i4i4) or alkoxy ammonium counter cations (N-ethyl-2-(2-methoxyethoxy)-N,N-bis(2-(2-methoxyethoxy)ethyl)ethan-1-ammonium bis(fluorosulfonyl)imide: N2(2O2O1)3) mixed at near 1:1 mol ratio with NaFSI. The conductivities of these electrolytes range from 4.4 mScm−1 for the smallest P111i4FSI:NaFSI system to 0.3 mScm−1 for the N2(2O2O1)3FSI:NaFSI mixture at 50 °C. This difference in conductivity is interestingly not reflected in the cyclic voltammetry for Na/Na+ where the maximum peak current density of 10 mAcm−2 is surprisingly high for the poorly conductive N2(20201)3FSI:NaFSI solution (e.g. 17 mAcm−2 for P111i4FSI:NaFSI). The overpotentials observed for Na symmetric cell cycling show very little differences after initial stabilising/conditioning for the three electrolytes being 50 mV for P111i4FSI:NaFSI and 100 mV for the others (at 0.1 mA cm−2). Also the Na+ transport number is similar for the three electrolytes ranging from 0.33 to 0.37. Full cells were prepared with layered transition metal oxide cathodes: O3-Na2/3(Fe2/3Mn1/3)O2), P2-Na2/3(Fe2/3Mn1/3)O2 and P2-Na2/3(Mn0.8Fe0.1Ti0.1)O2. While for the O3/P2-Na2/3(Fe2/3Mn1/3)O2 structures the device performance is consistent with the electrolyte properties, with the P2-Na2/3(Mn0.8Fe0.1Ti0.1)O2 cathode the N2(2O2O1)3FSI:NaFSI electrolyte cycling extremely well. The P111i4FSI and N2(2O2O1)3FSI yield almost equivalent specific capacities of approximately 180 and 160 mAhg−1 respectively at C/10 rate.

Interaction of testosterone-based compounds with dodecyl sulphate monolayers at the air-water interface.

A series of atomistic molecular dynamics simulations were performed for investigating the interactions between three different testosterone-based compounds (testosterone (T), testosterone propionate (TP) and testosterone enanthate (TE)) and sodium dodecyl sulphate (SDS) and ammonium dodecyl sulphate (ADS) monolayers, which vary only in the sodium or ammonium counterions used to neutralise the sulphate headgroup. These simulations were used to investigate how the structural and interfacial properties of the monolayer were affected by changing the number of drug molecules present per monolayer, and the chemical nature of the surfactant counterions and the testosterone-based compounds. Our results show that the structure of the interfacial water layer is affected by the change of the counterion but not the chemistry of the drug molecules. As a result of the difference in their chemical structure, the T, TP and TE drug molecules prefer different locations and orientations within the monolayers. Finally, we observed that the hydration of the drug molecules encapsulated within the ADS monolayers is significantly less than when they are encapsulated within the SDS monolayers. Understanding the role that the counterion and the chemistry of the drug molecules play in these systems provides us with a detailed description of the interactions that cause ADS micelles to encapsulate significantly less drug molecules than SDS micelles, which we have recently observed experimentally.

Catalytic enantioselective synthesis of atropisomeric biaryls by a cation-directed O-alkylation.

Axially chiral biaryls, as exemplified by 1,1'-bi-2-naphthol (BINOL), are key components of catalysts, natural products and medicines. These materials are synthesized conventionally in enantioenriched form through metal-mediated cross coupling, de novo construction of an aromatic ring, point-to-axial chirality transfer or an atropselective transformation of an existing biaryl. Here, we report a highly enantioselective organocatalytic method for the synthesis of atropisomeric biaryls by a cation-directed O-alkylation. Treatment of racemic 1-aryl-2-tetralones with a chiral quinidine-derived ammonium salt under basic conditions in the presence of an alkylating agent leads to atropselective O-alkylation with e.r. up to 98:2. Oxidation with DDQ gives access to C2-symmetric and non-symmetric BINOL derivatives without compromising e.r. We propose that the chiral ammonium counterion differentiates between rapidly equilibrating atropisomeric enolates, leading to highly atropselective O-alkylation. This dynamic kinetic resolution process offers a general approach to the synthesis of enantioenriched atropisomeric materials.

Catalytic Enantioselective Synthesis of C1‐ and C2‐Symmetric Spirobiindanones through Counterion‐Directed Enolate C‐Acylation

AbstractA catalytic enantioselective route to C1‐ and C2‐symmetric 2,2′‐spirobiindanones has been realized through an intramolecular enolate C‐acylation. This reaction employs a chiral ammonium counterion to direct the acylation of an in situ generated ketone enolate with a pentafluorophenyl ester. This reaction constitutes the first example of a direct catalytic enantioselective C‐acylation of a ketone and provides an efficient and highly enantioselective route to axially chiral spirobiindanediones. These products can be diastereoselectively derivatized, offering access to a range of functionalized spirocyclic architectures.

Catalytic Enantioselective Synthesis of C1 - and C2 -Symmetric Spirobiindanones through Counterion-Directed Enolate C-Acylation.

A catalytic enantioselective route to C1‐ and C2‐symmetric 2,2′‐spirobiindanones has been realized through an intramolecular enolate C‐acylation. This reaction employs a chiral ammonium counterion to direct the acylation of an in situ generated ketone enolate with a pentafluorophenyl ester. This reaction constitutes the first example of a direct catalytic enantioselective C‐acylation of a ketone and provides an efficient and highly enantioselective route to axially chiral spirobiindanediones. These products can be diastereoselectively derivatized, offering access to a range of functionalized spirocyclic architectures.

Catalytic Control in Cyclizations: From Computational Mechanistic Understanding to Selectivity Prediction.

This Account describes the use of quantum-chemical calculations to elucidate mechanisms and develop catalysts to accomplish highly selective cyclization reactions. Chemistry is awash with cyclic molecules, and the creation of rings is central to organic synthesis. Cyclization reactions, the formation of rings by the reaction of two ends of a linear precursor, have been instrumental in the development of predictive models for chemical reactivity, from Baldwin's classification and rules for ring closure to the Woodward and Hoffmann rules based on the conservation of orbital symmetry and beyond. Ring formation provides a productive and fertile testing ground for the exploration of catalytic mechanisms and chemo-, regio-, diastereo-, and enantioselectivity using computational and experimental approaches. This Account is organized around case studies from our laboratory and illustrates the ways in which computations provide a deeper understanding of the mechanisms of catalysis in 5-endo cyclizations and how computational predictions can lead to the development of new catalysts for enhanced stereoselectivities in asymmetric cycloisomerizations. We have explored the extent to which several cation-directed 5-endo ring-closing reactions may be considered as electrocyclic and demonstrated that reaction pathways and magnetic parameters of transition structures computed using quantum chemistry are inconsistent with this notion, instead favoring a polar mechanism. A rare example of selectivity in favor of 5-endo-trig ring closure is shown to result from subtle substrate effects that bias the reactant conformation out-of-plane, limiting the involvement of cyclic conjugation. The mode of action of a chiral ammonium counterion was deduced via conformational sampling of the transition state assembly and involves coordination to the substrate via a series of nonclassical hydrogen bonds. We describe how computational mechanistic understanding has led directly to the discovery of new catalyst structures for enantioselective cycloisomerizations. Calculations have revealed that stepwise C-C bond formation and proton transfer dictate the exclusive endo diastereoselectivity of the intramolecular Michael addition to form 2-azabicyclo[3.3.1]nonane skeletons catalyzed by primary amines. These insights have led to development of a highly enantioselective catalyst with higher atom economy than previous generations. This Account also explores transition-metal-catalyzed cycloisomerizations, where our theoretical investigations have uncovered an unexpected reaction pathway in the [5 + 2] cycloisomerization of ynamides. This has led to the design of new phosphoramidite ligands to enable double-stereodifferentiating cycloisomerizations in both matched and mismatched catalyst-substrate settings. Computational understanding of the factors responsible for the regio-, enantio-, and diasterocontrol is shown to generate tangible predictions leading to an acceleration of catalyst development for selective cyclizations.

Ionomers for Tunable Softening of Thermoplastic Polyurethane

Thermoplastic polyurethane (TPU) sulfonate ionomers with quaternary ammonium cations were synthesized to achieve soft TPUs without using conventional low molecular weight plasticizers. The sulfonated monomer N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES) neutralized with bulky ammonium counterions was incorporated as a chain extender to internally plasticize the TPU. Increasing the steric bulk of the counterion and the concentration of the ionic species produced softer TPUs with improved melt processability. The incorporation of the sulfonate species suppressed crystallinity of the TPU hard block, which was mainly responsible for the softening of the polymer. The synthetic procedure developed allows for facile tuning of the mechanical properties of the TPU by simply switching the counterion and/or increasing the feed ratio of ionic monomer. The precursors in this study were synthesized and analyzed via 1H NMR, and the thermomechanical properties of the resulting TPU ionomers were characterized b...

Spectroscopic and structural investigation of oxocarbon salts with tetraalkylammonium ions

In this study the synthesis, vibrational spectra (infrared and Raman) and crystal structures of three oxocarbon compounds with tetra-alkyl ammonium counter cations, namely [N(C3H7)4](HC4O4) (1), [N(C4H9)4]2[(C4O4) (H2C4O4)2] (2) and [N(C2H5)4]2(C5O5)·5H2O (3), have been reported. The supramolecular arrangement for all compounds as shown by x-ray diffraction indicate that strong donor (D)–acceptor (A) hydrogen bonds D–H…A are present in the dimer formation with monohydrogen squarate anion HC4O4− (2.503 Å) and for the trimer with two squaric acid moieties (H2C4O4) and the squarate dianion C4O42− (2.500 Å), for compounds 1 and 2, respectively. In contrast, compound 3 was stabilized through only averagely strong hydrogen bonds (2.735 Å) between all five oxygen atoms of the croconate dianion with different water molecules of crystallization of the supramolecular system. The presence of bands in the Raman spectrum at 1793 and 1670 cm−1 for compounds 1 and 2 have been assigned to the ν(CO), ν(CC) + ν(CO) modes, thus confirming the oxocarbon presence in the solid structure, as well as the bands at 1716 and 1601 cm−1 for compound 3, assigned to the ν(CO) and ν(CO) + ν(CC) + δ(CCC) + δ(CO) coupled modes of the associated croconate dianion (C5O52−). An important Raman signal observed for all structures can be seen at ca. 2950 cm−1 which is associated with the ν(CH2) and ν(CH3) stretching modes from the tetraalkylammonium cations.

Magnetically-induced ferroelectricity in the (ND4)2[FeCl5(D2O)] molecular compound

The number of magnetoelectric multiferroic materials reported to date is scarce, as magnetic structures that break inversion symmetry and induce an improper ferroelectric polarization typically arise through subtle competition between different magnetic interactions. The (NH4)2[FeCl5(H2O)] compound is a rare case where such improper ferroelectricity has been observed in a molecular material. We have used single crystal and powder neutron diffraction to obtain detailed solutions for the crystal and magnetic structures of (NH4)2[FeCl5(H2O)], from which we determined the mechanism of multiferroicity. From the crystal structure analysis, we observed an order-disorder phase transition related to the ordering of the ammonium counterion. We have determined the magnetic structure below TN, at 2 K and zero magnetic field, which corresponds to a cycloidal spin arrangement with magnetic moments contained in the ac-plane, propagating parallel to the c-axis. The observed ferroelectricity can be explained, from the obtained magnetic structure, via the inverse Dzyaloshinskii-Moriya mechanism.

Soluble Xanthate Compounds for the Solution Deposition of Metal Sulfide Thin Films

AbstractA series of soluble metal ethylxanthate compounds was synthesised as precursors for metal sulfide thin films to be deposited using solution‐based techniques. Initially, a range of air‐ and moisture‐stable organic ethylxanthate (EtXn) salts were synthesised (cation=Me4N (1), Et4N (2), Pr4N (3), Ph4P (4), guanidinium (5), NMeH3 (6), NMe2H2 (7), NMe3H (8), NH4 (9)). Thermogravimetric analysis (TGA) was used to examine their decomposition profiles, which in turn informed the decision of which counter cation was best suited for inclusion in the metal xanthate compounds. Periodic NMR spectroscopy studies and single‐crystal X‐ray diffraction (SXRD) were used to determine the role protic ammonium counter cations play in the detrimental conversion of xanthates to dithiocarbamate anions. The organic salts 1 and 4 were used to form the metal ethylxanthate compounds (Me4N)[M(EtXn)x] (x=3 for M=Cd (10 Cd), Ni (10 Ni), Zn (10 Zn); x=4 for M=La (11 La)) and (Ph4P)[M(EtXn)3] (M=Cd (12 Cd), Ni (12 Ni), Zn (12 Zn)). Solubility studies on these compounds were performed using a range of solvents to demonstrate the viability of using these compounds for solution‐based deposition methods for thin‐film formation. TGA of the metal xanthate compounds was used to examine their thermal‐decomposition profiles and the product resulting from thermolysis was found to be the respective metal sulfide. In addition, the coproducts of thermal decomposition were analysed by headspace gas‐chromatography mass spectrometry (HS GC–MS) to probe the decomposition mechanism of the precursors. In situ variable‐temperature synchrotron XRD studies on both bulk and thin‐film samples of 10 Cd and 12 Cd were used to examine metal sulfide crystalline phase formation. Decomposition of both precursors was found to give CdS in a hexagonal phase, with the addition of CdCl2 found to aid in increasing the crystallite size during crystallisation.

Effects of counterion structure on the surface activities of anionic fluorinated surfactants whose counterions are organic ammonium ions

The surface tension of dialkylammonium perfluorooctanoate [C7F15COONH2(CnH2n+1)2, n=1–4], dialkylammonium perfluorooctylsulfonate [C8F17SO3NH2(CnH2n+1)2, n=1–4] and trialkylammonium perfluorooctylsulfonate [C8F17SO3NH(CnH2n+1)3, n=1–4] in aqueous solution was measured by drop volume method at 25°C. The critical micelle concentration (cmc), the surface tension at cmc (γcmc), the maximum amount adsorbed (Γmax) and the minimum molecular area (Amin) in the surface adsorption layer were obtained. Because of the limited solubility for C7F15COONH2(C4H9)2, C8F17SO3NH2(C4H9)2 and C8F17SO3NH(C4H9)3 at 25°C, their cmc and γcmc values could not be successfully obtained. Combining with other series in previous works, an overview picture for the effects of organic ammonium counterions on anionic fluorinated surfactants could be drawn. The rules for the interactions between organic ammonium ions and surfactive anions were summarized (including headgroup type, the chain length of fluorinated hydrophobic tail, and the substituent number, the alkyl chain length and the presence of hydroxyl groups in counterion structure). The mechanism behind these rules was discussed in detail, relying on the electrostatic, hydrophobic and steric factors.

Preparation and Characterisation of complex Bis(pentafluorophenyl) antimony(V) anions of the type [(Rf)2SbCl3X

A series of hiteherto unreported solid salts of hexa-coordinated anions of the general formula [(Rf)2SbCl3X]- , where Rf = C6F5 ; L = Cl and X = Cl, Br, I, N3, NCS and SeCN have been prepared in the presence of tetraorgano ammonium, phosphonium, arsonium and stibonium counter ions. The complexes have been formulated and characterised on the basis of elemental analysis, molar conductances, molecular weights and solid state IR, solution state 1H NMR and 19F NMR spectral data. The physico-chemical data are consistent with six-coordinate antimony complexes.DOI: http://dx.doi.org/10.3126/ijasbt.v1i3.8304 Int J Appl Sci Biotechnol, Vol. 1(3) 2013 : 90-96

Nonanuclear lanthanide(III) nanoclusters: Structure, luminescence and magnetic properties

A series of nonanuclear lanthanide(III) nanoclusters, (CH3)3NH[Ln9(L)16(μ3-OH)8(μ5-O)2](CH3OH) where Ln=Nd, Eu, Tb, Gd, Dy, Er, Yb and HL=(2-hydroxy-5-methylphenyl)propan-1-one, was successfully synthesized and characterized by photoluminescence, magnetic susceptibility and X-ray crystallography. (CH3)3NH[Gd9(L)16(μ3-OH)8(μ5-O)2](CH3OH) crystallized in the monoclinic space group C2/c, with a monovalent anionic cluster and a tertiary ammonium counter ion. Temperature dependent photoluminescence studies of ((CH3)3NH)0.5[Eu9(L)16(μ3-OH)8(μ5-O)2](H2O)5 highlights the presence of two distinct metal centers and temperature dependent magnetic susceptibilities for both ((CH3)3NH)0.5[Dy9(L)16(μ3-OH)8(μ5-O)2](H2O)4 and ((CH3)3NH)0.5[Tb9(L)16(μ3-OH)8(μ5-O)2](H2O)5 suggest weak antiferromagnetic interactions between the lanthanide(III) ions.

Synthesis and Polymerization of Substituted Ammonium Sulfonate Monomers for Advanced Materials Applications

Sulfonated polymers have found use as ion-exchange membranes for use in fuel cells, water purification, electroactive devices, and inorganic materials templating and synthesis. Improving the materials for these applications and opening up new applications requires the ability to synthesis targeted or more complex sulfonated polymers, which includes tailoring the chemistry (copolymerization across a wider range of solubility) and/or polymer architecture (block, graft, nanoparticle). This article will summarize the recent work using sulfonated monomers with substituted ammonium counterions as a versatile route for enabling this goal. Two main benefits of these monomers are as follows. First, they are useful for preparing amphiphilic copolymers, which is a challenge using traditional acidic or alkali salt forms of sulfonated monomers. Second, sulfonated polymers with substituted ammonium counterions are useful polymers for obtaining unique material properties, such as organo-gelation of low polarity solvents or obtaining ionic liquid polymers for the fabrication of solid polymer electrolytes.

A Marriage of POM and MOF

Chemistry![Figure][1] CREDIT: SONG ET AL., J. AM. CHEM. SOC. 133 , 10.1021/JA203695H (2011) Polyoxometalates (POMs) are clusters, typically bearing a net negative charge, that assemble from multiple metal oxide units sharing oxygens and have shown useful catalytic activity for a range of organic oxidation reactions. Metal organic framework (MOF) materials are three-dimensional porous structures that can be designed with specific pore size and composition. As such, they have found use for gas adsorption, separation, and in some cases catalysis. Song et al. show that the Keggin-type POM [CuPW11O39]5− can fit snugly into the pores of MOF-199, leading to a strong enhancement of catalytic properties for the oxidation of thiols to disulfi des and the removal of hydrogen sulfide. Analysis of the unit cells shows that the MOF remains intact after inclusion of the POM and associated (tetramethyl)ammonium counter-ion into adjacent large and small pores, and that 50% of the large pores remain empty, allowing for easy movement of reactants and products. Aerobic H2S oxidation was achieved from aqueous solutions at a rate of 4000 turnovers within 20 hours and was also observed under gas-phase conditions but with lower turnover as the pores were blocked by sulfur accumulation. Tests with a non–copper-containing POM did not show catalytic activity, indicating that the Cu centers in the POM unit are probably the active sites. Air-based oxidations of thiols to disulfides showed excellent selectivity, although decreasing yield as the size of the thiol substituents increased, leading to steric hindrance within the MOF. J. Am. Chem. Soc. 133 , 10.1021/ja203695h (2011). [1]: pending:yes

Anionic Surfactants and Surfactant Ionic Liquids with Quaternary Ammonium Counterions

Small-angle neutron scattering and surface tension have been used to characterize a class of surfactants (SURFs), including surfactant ionic liquids (SAILs). These SURFs and SAILs are based on organic surfactant anions (single-tail dodecyl sulfate, DS, double-chain aerosol-OT, AOT, and the trichain, TC) with substituted quaternary ammonium cations. This class of surfactants can be obtained by straightforward chemistry, being cheaper and more environmentally benign than standard cationic SAILs. A surprising aspect of the results is that, broadly speaking, the physicochemical properties of these SURFs and SAILs are dominated by the nature of the surfactant anion and that the chemical structure of the added cation plays only a secondary role.

Collision-induced gas-phase reactions of perhalogenated closo-dodecaborate clusters – a comparative study

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.