Bare Metal Ions Research Articles

Ion Spray Mass Spectrometry for Elemental Speciation in Aqueous Samples: Preliminary Investigation of Experimental Parameters, Matrix Effects and Metal–Ligand Complexation

Ion spray mass spectra obtained from aqueous solutions are discussed. Ion clusters with large numbers of water molecules, very few water molecules or bare elemental ions could be obtained by adjusting the sampling orifice voltage, the skimmer voltage or the position of the ion spray nebulizer relative to the sampling orifice. In some cases submillimeter changes in the position of the ion spray nebulizer can dramatically affect the nature of the spectra observed. There is evidence of declustering between the skimmer and first ion lens as well as between the sampling orifice and skimmer. Interpretation of the mass spectra must be carried out with care as potential spectral overlaps are common. Use of a triple quadrupole mass spectrometer allows assessment of potential spectral overlaps. Ni–EDTA complexation was investigated. The Ni + signal correlated with the expected concentration of free metal ions in the solution not the total metal concentration even when relatively harsh conditions that produced bare metal ion spectra were used. Matrix effects due to high concentrations of NaCl and HCl were briefly investigated.

Collisional fragmentation of endohedral fullerenes

The fragmentation patterns of the endohedral fullerenes ions, (Gd@C 82) + and (La@C 82) +, produced by energetic collisions with various atomic and molecular targets have been measured over an entire mass range extending from the parent endohedral to the bare metal ion. The fragmentation spectra confirm the endohedral nature of these fullerenes by the production of singly and doubly charged endohedral fragments M@C 2 n (30 ⩽ n ⩽ 40). The fragmentation pattern includes a substantial component of empty fullerenes that extend from C 80 to less than C 60 dependent on the collision partner. The empty fullerenes are accompanied by small metal-containing fragment ions, MC 2 n + (0 ⩽ n ⩽ 5), produced in hard central collisions with the target atom. The distribution of MC 2 n + fragments differs for the two endohedrals and is dependent on the collision partner.

Evidence for catalytic formation of benzene from ethylene on tungsten ions

The gas-phase reactivity of tungsten cations with ethylene was investigated by means of Fourier-transform ion cyclotron resonance mass spectrometry. The ethylene adsorbs on the W + with partial dehy drogenation, forming W (C 2 H 2) n + cluster ions. Up to nine ethylenes can be consecutively added, n = 1–9. Collision-induced dissociation (CID) experiments provide evidence that a dehydrogenative oligomerization and formation of benzene takes place on the tungsten cation. The dominating fragmentation channel of the WC 6H 6 + ion results in appearance of the bare metal ion, suggesting that a C 6H 6 fragment, most likely benzene, was formed.

Electrospray Mass Spectra of Lanthanides

The electrospray mass spectra of several elements in the lanthanide series are presented with the focus being on understanding the basic processes that occur to yield such spectra. The solution chemistry and the physical properties of the elements have a profound effect on the type of species observed in a mass spectrum. To perform elemental analysis by electrospray mass spectrometry, harsh declustering conditions are typically used. This results in a spectrum consisting of the bare metal ion (Ln[sup +] or Ln[sup 2+]) and molecular ions (LnO[sup +]) such as oxides as well as contributions due to matrix ions. The sampling conditions required to obtain such spectra require a large potential difference between the sampling plate and the skimmer at the atmosphere to vacuum interface, resulting in efficient collision-induced dissociation conditions. To monitor the process, a frame by frame illustration is used where the potential difference between the sampling plate and skimmer is increased in increments and the resultant spectra are captured. With this procedure, the dominant processes may be highlighted and explained step by step and a clearer understanding of the processes involved is obtained. 43 refs., 7 refs., 1 tab.

Bond activation by d0 metal carbene complexes in the gas phase

AbstractThe formation and bond activation reactions of the d0 carbene complexes MCHCN+ (M = Sc, Y) are presented. Sc+ and Y+ dehydrogenate acetonitrile to produce the metallocarbenes. The carbene complexes are less reactive towards hydrocarbons than their bare metal ion counterparts, but will activate CH, OH, and NH bonds through a four‐centered intermediate. Labeling studies indicate that reactions with olefins proceed by migratory insertion after initial CH activation, and that subsequent ligand coupling produces metal‐bound nitrite products. Oletin metathesis reactions are not observed due to the electron‐withdrawing characteristics of the CN substituent and the electrophilicity of the metal centers.

Effects of ligands on the reactivity of V + and Ti + toward dehydrogenation of ethylene

In this communication, we report studies of the dehydrogenation reactivity of bare Ti + and V +, as well as their coordinated complexes, toward ethylene at thermal energies, where the ligands are acetylene or ethylene for Ti +, and ethylene for V +. We have observed that coordinated Ti + and V + complexes show quite different reactivity from that of the bare metal ions, and that the effects of ligands on the reactivity depend strongly on the number of these as well as the type of metal ion. For both metal ions, the three-ligand coordinated species display higher dehydrogenation reactivity than the one- and two-ligand coordinated complexes.

Charge stripping as a probe to determine the effects of ligation in metal ion complexes produced in a fast atom bombardment source

Fast atom bombardment ionisation is combined with charge stripping (CS) to produce bare and ligated metal dications. Abundant quantities of ions resulting from the bombardment of transition and lanthanide metal salts are produced and charge stripped. Q min values obtained from the CS spectra agree within ± 0.5 eV of the respective second ionisation energies for the bare metal ions. Effects of ligands such as Cl and OH are observed as an increase in Q min values relative to the bare metals ions, e.g. Δ Q min = 0.9 eV for CoCl + and Δ Q min = 3.2 eV for HoCl +.

Metal ion catalysis in nucleophilic displacement reactions at carbon, phosphorus, and sulfur centers. III. Catalysis vs. inhibition by metal ions in the reaction of p-nitrophenyl benzenesulfonate with ethoxide

The rate of the nucleophilic displacement reaction of p-nitrophenyl benzenesulfonate (1) with alkali metal ethoxides in ethanol at 25 °C has been studied by spectrophotometric techniques. For lithium ethoxide, sodium ethoxide, potassium ethoxide, and cesium ethoxide, the observed rate constants increase in the order LiOEt < NaOEt < CsOEt < KOEt. The effect of added crown ether and cryptand complexing agents was also investigated. Addition of complexing agent to the reaction of KOEt results in the rate decreasing to a minimum value corresponding to the reaction of free ethoxide. Conversely, addition of complexing agent to the reaction of LiOEt results in the rate increasing to a maximum value that is identical to the minimum value seen in the reaction of KOEt in the presence of excess complexing agent. In complementary experiments, alkali metal ions were added in the form of unreactive salts. Addition of a K+ salt to the reaction of KOEt increases the reaction rate, while addition of a Li+ salt to the reaction of LiOEt decreases the rate. The involvement of metal ions in the reaction of 1 is proposed to occur via reactive alkali metal – ethoxide ion pairs. The kinetic data are analyzed in terms of an ion pairing treatment that allows the calculation of second-order rate constants for free ethoxide and metal–ethoxide ion pairs; the rate constants increase in the order LiOEt < EtO−< NaOEt < CsOEt < KOEt. Thus, Li+isaninhibitorofthereactionofethoxidewith1, whiletheothermetalsionsstudiedareallcatalysts. Equilibrium constants for the association of the various metal ions with the transition state are calculated using a thermodynamic cycle, and are compared to association constants in the ground state. Consistent with the observed kinetic results, Li+ is found to stabilize the ground state more than the transition state, while Na+, K+, and Cs+ all stabilize the transition state more than the ground state. The trend in the magnitude of the transition state stabilization is interpreted in terms of interactions of the transition state with bare or solvated metal ions. It is concluded that the transition state for the reaction of 1 with ethoxide forms solvent separated ion pairs with alkali metal ions. Analogous data were available for the reaction of p-nitrophenyl diphenylphosphinate (2) with ethoxides, where Li+, Na+, K+, and Cs+ all function as catalysts, and the results are analyzed as above. In contrast to the sulfonate system, it is proposed that the phosphinate transition state forms contact ion pairs with alkali metal ions. The difference is attributed to a greater localization of negative charge in the phosphinate transition state, leading to stronger interactions with metal ions, which overcome metal ion – solvent interactions. Keywords: nucleophilic substitution at sulfur, alkali metal ion catalysis.

Evidence for the activation of unstrained carbon-carbon bonds by bare transition metal ions M+ (M = Fe, Co) without prior C-H bond activation

The metastable ion (MI) decompositions of RNH 2 /M + complexes (R = (C 2 H 5 ) 2 CHCH 2 , C 2 H 5 C(CH 3 ) 2 CH 2 ; M=Fe, Co) in the gas phase have been studied by tandem mass spectrometry with a four-sector instrument of BEBE configuration. The analyses of the MI spectra of isotopically labeled complexes uncover processes which inter alia demonstrate that the loss of C 4 H 8 corresponds to a reaction in which site-specific oxidative addition of an unstrained C-C bond to the «anchored» transition-metal ion M + takes place without prior C-H bond activation. The intramolecular methyl migration preceding the elimination of C 4 H 8 is subject to a secondary kinetic isotope effect of k H /k D = 1.33 for M + = Fe + and k H /k D = 1.15 for M + = Co + per D atom. Additional processes observed correspond to the generation of molecular hydrogen, methane, ethylene and ethane. All reactions are highly specific, and mechanisms are suggested that are in keeping with the labeling data

Revised and modified mechanisms for the reactions of bare transition metal ions M+ (M = Fe, Co, Ni) with n-C3H7X (X = NH2, OH) in the gas phase

Etude de la decomposition des ions metastables des complexes n-C 3 H 7 X/M + (X=OH,NH 2 ;M=Fe,CO,Ni) en phase gazeuse par spectrometrie de masse tandem

Laser-Stimulated Noble Metal Deposition From Gaseous and Condensed Acetylacetonates. Photoreactions in the Supersonic Jet and Above Silicon

ABSTRACTLaser-stimulated deposition from the acetylacetonates of Pt and Ir has been found to take place on silicon surfaces. The gas phase photoreactions have been observed in a supersonic free jet TOF mass spectrometer and above silicon. The bare metal ions and metal cluster ions are formed from the complexes in the gas by multiphoton excitation. On the substrates deposits are detected by microprobe analysis with a metal content higher than 95 %. Also from condensed complexes laser-induced metal deposition, and as competitive process photodesorption, takes place.

Complexes of vitamin B 6—XVIII. Ternary and quaternary complexes involving pyridoxamine, glycylglycine and imidazole and some bivalent metal ions

The formation constants of ternary and quaternary complexes containing the ligands pyridoxamine, glycylglycine and imidazole with Co(II), Ni(II), Zn(II) and Cd(II) were determined by pH-metric titration in 0.15 M NaNO 3 at 37°C using the MINIQUAD-75 program. It has been shown that the logarithms of the ternary formation constants are linear increasing functions of the sum of the logarithms of the first protonation constants of the ligands, but the log K I (MLH m +ML′H m ⇌ K I MLL′H s ) are linear decreasing functions. It has been shown that deprotonation of the peptidic group is prohibited in ternary and quaternary metal complexes. It is also found that the imidazole moiety favourably ligates the ternary complexes rather than the bare metal ions.

Gas-phase reactions of MS + ions (M = Fe, Co, Ni) with alkanes. An FTMS study

The gas-phase reactions of MS + ions (M = Fe, Co, Ni) with small alkanes are reported. MS + reacts with hydrocarbons primarily by H 2S loss from the collision complex. This complex can further dissociate by dehydrogenation, creating a metal-polyolefin complex, or by loss of small alkenes. These latter dissociations are similar to the collision-induced dissociation decomposition pathways for the metal-olefin complex and suggest that H 2S loss leaves an internally excited metal-olefin complex. As has been observed for a variety of mono-ligated metal species, MS + shows a preference for CH bond insertion, leading to dehydrogenation, compared with the bare metal ions which predominantly attack CC bonds. The sulfur ligand does not activate reactions as much as an oxygen ligand, which may be attributed to the fact that H 2S loss is less exothermic than H 2O loss. Photodissociation threshold measurements yield D° (FE + −S) = 65 ± 5 kcal mol −1, D°(Co + −S) = 62 ± 5 kcal mol −1, and D°(Ni + −S) = 60 ± 5 kcal mol −1, from which additional thermochemical information is derived.

Catalytic activity of alkaline-earth Y zeolites and concentration of bare metal ions located in the site II of faujasite structure

The concentration of the bare metal ions located in the Site II of the alkaline-earth Y zeolites was determined from the CO adsorption, and the concentration sequence was obtained as follows: SrY>CaY>MgY>BeY. This sequence corresponded well to the radius of exchanged cation. Catalytic activity of alkaline-earth Y zeolites for the disproportionation reaction of NO, further, was discussed, and activity order of per unit amount of bare Site II cation was determined as follows: BeY>MgY>CaY>SrY>BaY. This order corresponded well to the strength of the electrostatic field of alkaline-earth Y zeolites.

Valence‐change in the mass spectra of metal complexes

AbstractA review article is presented relating to the concept of valence‐change in the mass spectra of metal‐containing compounds. It is found that the modes of ion dissociation in these spectra are markedly dependent on the oxidation states normally assumed by the metal concerned and it is postulated that electron‐transfer may be possible between the complexed metal atom and its ligands in the ion, such that the odd‐ or even‐electron character of the ion is inter‐changeable. Ion reactions such as the consecutive loss of two radicals are normally of low probability in the mass spectra of organic compounds, but are often observed in the mass spectra of metal‐containing compounds and can be rationalized in terms of the valence‐change concept. Convincing evidence for valence‐change in some spectra is provided by the occurrence of reactions leading to the bare metal ion, or to the loss of neutral fragments containing the metal atom in a lower oxidation state than in the precursor molecule. Further applications of the concept may be found in the rationalization of the mass spectra of inorganic and organometallic compounds.