ChemInform Abstract: Some General Aspects of the Chemistry of Organo-Alkali Metal Ions. An Overview of Recent Work (original) (raw)
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Some general aspects of the chemistry of Organo-alkali metal ions. An overview of recent work
International Journal of Mass Spectrometry and Ion Processes, 1987
Organo-alkali metal ions of the type [M + xNa-(x-l)H]+ (x = l-3) are commonly observed in the desorption ionization mass spectra of polar organic molecules. An overview of our work on the formation and selected applications of organo-alkali metal ions is presented. We interpret our data as evidence that ions of the type [M + xA-(x-l)H]+ are formed from [M+ A(AX),]+ cluster ions. Another important aspect of this work deals with the dissociation reactions of organo-alkali metal ions. We have found that structurally significant fragment ions are observed in the collision-induced dissociation (CID) spectra of [M+A]+ ions that are not observed in the [M+H]+ ion CID spectrum. We attribute these differences to functional group basicity and organo-alkali metal ion binding energies. That is, alkali metal ions are bound to specific sites of the organic molecule and the fragment ions formed upon CID are indications of the structure of the ionic organo-alkali metal ion complex.
Inorganica Chimica Acta, 1995
A negative ion electrospray mass spectrometric study of COII@X~S in solution formed between uninegative tripodal oxygen or nitrogen ligands and alkali metal ions and alkali metal halides Abstract Negative ion electrospray mass spectra have been observed from 5050 i-propanol/water solution for the sodium salts of uninegative tripodal oxygen ligands of the type [(CJ-i,)C@(0)(OR)z},l-(=[L]-) (R=Me, Et, i-Pr) and solutions of the potassium salt of the uninegative tripodal hydridotris(pyrazole)borate ligand [HB(pz),]-. The sodium salts of the oxygen ligands all give negative ion ES mass spectra which show not only a peak due to the free anion, but also other peaks which may be assigned to [NaLJI-, [Na&]-, and in the case of R=Me even [Na3L,]-. These results are consistent with the known trimeric and polymeric structures of the sodium salts of several of these type of organometallic ligands confirming that these oligomeric structures are at least partially retained in solution. Addition of alkali and metal halides to the solutions of NaL leads to negative ion ES mass spectra showing ions assigned to alkali metal halide adducts of the types {[L]-+n(NaCl)} (n-l-9) and {[NaL]-+n(NaCl)} (n = l-g) etc. Fewer alkali metal halides are adducted to the anions with larger alkali metal ions. Lithium chloricje also strongly adducts to [L]-, but it causes dissociation of the associated species containing more than one [L]-group. In contrast, only [HB(pz),]-and [KjHB(pz),},]-are observed in the negative ion ES mass spectrum of K[HB(pz),] and alkali metal halides do not form observable adducts with this anion. Keyword: Electrospray mass spectrometry; Alkali metal ion complexes; Alkali metal halide complexes; Tripodal oxygen or nitrogen ligand compIexes * Corresponding author. 0020-1693/95/$09.50 6 1995 Else-vier Science S.A. All rights reserved SSDI 0020-1693(94)04397-E
Dissociation of polyether-transition metal ion dimer complexes in a quadrupole ion trap
Journal of the American Society for Mass Spectrometry, 1997
The formation and dissociation of dimer complexes consisting of a transition metal ion and two polyether ligands is examined in a quadrupole ion trap mass spectrometer. Reactions of three transition metals (Ni, Cu, Co) with three crown ethers and four acyclic ethers (glymes) are studied. Singly charged species are created from ion-molecule reactions between laserdesorbed monopositive metal ions and the neutral polyethers. Doubly charged complexes are generated from electrospray ionization of solutions containing metal salts and polyethers. For the singly charged complexes, the capability for dimer formation by the ethers is dependent on the number of available coordination sites on the ligand and its ability to fully coordinate the metal ion. For example, l&crown-6 never forms dimer complexes, but 12-crown4 readily forms dimers. For the more flexible acyclic ethers, the ligands that have four or more oxygen atoms do not form dimer complexes because the acyclic ligands have sufficient flexibility to wrap around the metal ion and prevent attachment of a second ligand. For the doubly charged complexes, dimers are observed for all of the crown ethers and glymes, thus showing no dependence on the flexibility or number of coordination sites of the polyether. The nonselectivity of dimer formation is attributed to the higher charge density of the doubly charged metal center, resulting in stronger coordination abilities. Collisionally activated dissociation is used to evaluate the structures of the metal-polyether dimer complexes. Radical fragmentation processes are observed for some of the singly charged dimer complexes because these pathways allow the monopositive metal ion to attain a more favorable 2 + oxidation state. These radical losses are observed for the dimer complexes but not for the monomer complexes because the dimer structures have two independent ligands, a feature that enhances the coordination geometry of the complex and allows more flexibility for the rearrangements necessary for loss of radical species. Dissociation of the doubly charged complexes generated by electrospray ionization does not result in losses of radical neutrals because the metal ions already exist in favorable 2+ oxidation states. (J Am Sot Mass Spectrom 1997,8,620-629) 0 1997 American Society for Mass Spectrometry T he examination of reactions of metal ions with organic ligands in the gas phase has been an ongoing field of research over the past two decades because of both the fundamental interest in metal ion chemistry [ l---8] and the interesting analogies between solution and gas-phase chemistry. Recent advances in mass spectrometry have allowed the generation of selectivity solvated metal complexes [g-lo], measurement of binding energies of metal-containing clusters 18-111, and elucidation of metal binding sites of oligonucleotides [12], to name just a few of the active areas of research involving metal complexation in the gas phase. Metal complexation has also been viewed as a versatile method of ionizing molecules, and there have been numerous reports of metal complexation in fast-atom bombardment (FAB) [13-181 or electrospray ionization (ESI) mass spectrometry Address reprint requests to Jennifer Brodbelt, resulting in the creation of stable complexes, such as those containing saccharides or peptides.
The Journal of Physical Chemistry A, 1997
Bond dissociation energies of Na + [O(CH 3 ) 2 ] x , x ) 1-4; Na + [(CH 2 OCH 3 ) 2 ] x , x ) 1 and 2; and Na + [c-(C 2 H 4 O) 4 ] are reported. The bond dissociation energies are determined experimentally by analysis of the thresholds for collision-induced dissociation of the cation-ether complexes by xenon measured using guided ion beam mass spectrometry. In all cases, the primary and lowest energy dissociation channel observed experimentally is endothermic loss of one ligand molecule. The cross section thresholds are interpreted to yield 0 and 298 K bond dissociation energies after accounting for the effects of multiple ion-molecule collisions, internal energy of the complexes, and unimolecular decay rates. Trends in the bond dissociation energies determined by experiment and recent theoretical ab initio calculations are in good agreement. Our best experimental values, which have an average uncertainty of (7 kJ/mol, are lower than the theoretical values by 7 ( 5 kJ/mol per metal-oxygen interaction. These values are compared with bond dissociation energies for the comparable lithium cation-ether complexes. This comparison reveals the thermodynamic consequences of ligand-ligand repulsion.
Journal of the American Chemical Society, 1992
Ion/molecule reactions are used to demonstrate that mass-selected C2H3O+ and C2H3S+ ions have distinctive reactivities which depend on the precursor molecule from which they are generated. Several isomers of both ions are distinguished, and the mechanisms of their reactions are elucidated. Structural characterization of the ion/molecule products is achieved in multistage (MS3) experiments. In reactions with isoprene, the acetyl cation (a) is unique in that it displays a [4 + 2+] Diels-Alder cycloaddition product while other C2H30+ isomers, 0-protonated ketene (b) and the oxiranyl cation (c), as well as the isobar C3H7+, undergo proton-transfer reactions. The proportion of the acetyl ion in m/z 43 ion mixtures is estimated by comparing the extent to which cycloaddition and proton transfer take place. On this basis, compounds with various functionalities are ordered in terms of the degree to which their m/z 43 fragments comprise the acetyl cation. Correlations are developed with the degree of enolization in the molecular ions of the precursors. Further distinction of C2H3O' isomers 81: is achieved in reactions with methylanisoles. Ion a preferentially forms the intact adduct with these reagents while ions b and c fail to do so, their spectra being dominated by characteristic charge-exchange, proton-transfer,, and adduct-fragmentation products. Ion c reacts with m-and o-methylanisole by a process which formally corresponds to CH+ addition to the neutral molecule. Reaction with p-methylanisole shows predominant formation of the CH2'+ addition product. Sequential product MS3 spectra show that methyne addition yields m-and o-methylmethoxytropylium ions, while methylene addition yields ionized 2,4-dimethylanisole. The C2H3S+ ions formed from a variety of precursors show similar product spectra upon reaction with isoprene, all displaying abundant cycloaddition products. Sequential product spectra are identical, a result that indicates formation of a common adduct. Reaction with m-methylanisole, however, allows distinction of the isomeric C2H3S+ ions and shows that the failure to distinguish these isomers by reaction with isoprene is the result of isomerization of the different cycloaddition products to a common structure. Similarly, failure to distinguish the C2H3S+ ions by previous collision-induced-dissociation experiments is interpreted to be a result of isomerization after collision, not of the existence of a single ionic population. These results provide an illustration of the detailed information on ions which is possible using ion/molecule reactions and the degree to which the structures of ion/molecule reaction products can be elucidated using multistage (pentaquadrupole) mass spectrometry. On leave from Universidade Estadual de Campinas, Caixa Postal 6154, 1308 1 Campinas, SsIo Paulo, Brazil.
Chemical Physics Letters, 1979
Bemd M_ RODE and Hans G_ KRAFT hstitut fw AnorgnniscIxe und Anatytische Chemie der Llnirershir Znnsbruck, A-6020 Innsbruck, Austrih Received 13 November i978 _4t, initio MO SCF cdcuIations on the complexes of Li. Na, K, Be, Mg and Ca ions ~5th glyo?tal have been performed. These calcu!atiom represent the fust part ofa series of theoretical investigations on the dependence of complex formation properties ofhgands containing tw.o carbonyl groups on the structure of the coordinative center. Special attention has been paid to the chelate effect, Rhich is found to increase with increasing atomic number within the series of ions. The cakuiated values ;LTe compared with our recent data obtained from W spectroscopy of ion complexes with dicarbonyl Iigands