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Interactions of cycloheptatriene derivatives, C7H6X, (X = NH, PH, AsH, O, S, Se) with the cations H+, CH3+, Cu+, Al+, Li+, Na+, and K+ are studied using B3LYP functional and 6-311++G(d,p) basis set. The calculated gas-phase cation affinities (CA) and cation basicities (CB) for all molecules decrease as H+ > CH3+ > Cu+ > Al+ > Li+ > Na+ > K+. We used the induced aromaticity in the 7-membered ring of C7H6X upon interaction with the cations, M+, as a measure of C7H6X/M+ interaction. Nucleus-independent chemical shift (NICS) and harmonic oscillator model of aromaticity (HOMA) were used as two indices of aromaticity. The highest and lowest induced aromaticities were observed for interactions of H+ and K+, respectively. Also, the aromaticity induced by interaction with a cation in C7H6AsH and C7H6PH was larger than that in C7H6NH and C7H6O. Hence, the aromaticity was considered as a measure of covalency for the C7H6X/M+ interactions showing a rational dependence on both the molecule and cation. The nature of the interactions was also assessed using electron density, charge distribution analysis and NBO calculations. The results of the aromaticity indices, NICS and HOMA, were compared with the electron density and NBO results. [ABSTRACT FROM AUTHOR]

[Display omitted] Interactions of three simple Lewis bases (LB) of varying strength: H 2 O, NH 3 , and CH 2 O with Noble gas (Ng) cations He+, Ne+, Ar+, Kr+, Xe+ were studied using the MP2 and CCSD(T) methods. Ng+ and LBs react via two competing pathways, charge exchange reaction and cationic adduct formation. Two kinds of [Ng/LB]+ adducts were obtained after geometry optimization. In most cases, the hydrogen atoms of the LBs were the most favored sites for interactions with Ng+. Exceptions were observed for the [Xe/NH 3 ]+, [Xe/H 2 O]+, and [Kr/H 2 O]+ systems in which interaction is via their N and O atoms. We showed that fluorination of the LBs increases their ionization energies, avoiding charge transfer, hence, F 2 O, NF 3 , and CF 2 O can act as LBs interacting with Ng+ via their O and N atoms. Using fluorination of the Lewis bases, the formation of [Kr/CF 2 O]+, [Kr/NF 3 ]+, [Xe/CF 2 O]+, and [Xe/NF 3 ]+ was more favorable than charge exchange reaction. [ABSTRACT FROM AUTHOR]

Relationship between the C≡O-X+ (X = H, Li, Na, K, Al, Cu) angle and covalent characteristic of the X+-M (M = CH2O, CH3CHO, acetone, imidazol-2-one (C2H2N2O), cytosine, γ-butyrolactone) was investigated, theoretically. The calculated electron densities ρ at the bond critical points revealed that the covalency of the M-X+ interaction depended on the nature of the cation and varied as H+ > Cu+ > Al+ > Li+ > Na+ > K+. The alkali cations tended to participate in electrostatic interactions and aligned with the direction of the molecule dipole or local dipole of C≡O group to form linear C≡O-X geometries. Because of overlapping with lone-pair electrons of the sp² carbonyl oxygen, the H+ and Cu+ formed a bent C≡O-X angle. Al+ displayed an intermediate behavior; the C≡O-Al angle was 180° in [CH2O/Al]+ (mainly electrostatic), but when the angle was bent (146°) under the effect of local dipole of an adjacent imine group in cytosine, the covalency of the CO-Al+ interaction increased. The C≡O-X angles in M/X+ adduct ions were scanned in different O-X bond lengths. It was found that the most favorable C≡O-X angle depended on the O-X bond length. This dependency was attributed to variation of covalent and electrostatic contributions with O-X distance. In addition, the structures of [CH2S/X]+ and [CH2Se/X]+ were studied, and only bent C≡S-X and C≡Se-X angles were obtained for all cations, although the dipole vectors of CH2S and CH2Se coincide with the C≡S and C≡Se bonds. The bending of the C≡S-X and C≡Se-X angles was attributed to the covalent characteristic of S-X and Se-X interactions due to high polarizability of S and Se atoms. [ABSTRACT FROM AUTHOR]

The effect of Cs+ ligation on the decarboxylation of malonic acids (unsubstituted and methyl-, dimethyl-, ethyl-, and phenyl-substituted) in their carboxylate form was studied in the gas phase using tandem mass spectrometry. The study is based on the comparison of the decarboxylation of the bare monoanion (hydrogen malonates) and of the cesium adduct of the cesium salt (Cs+[cesium hydrogen malonates]) under collisional activation. Energy-resolved dissociation curves of the negative and positive ions exhibit major differences. Decarboxylation of the cationic adducts of substituted malonic acid salts occurs at significantly lower collisional activation than for the corresponding bare hydrogen malonate anions. The conclusions from these experiments are supported by DFT calculations. The calculated activation parameters (enthalpy and Gibbs energy) confirm that the cesium cation coordination assists the decarboxylation of the carboxylate form. [ABSTRACT FROM AUTHOR]

The interaction between the cesium cation and fulvic or humic acids is supposed to play a role in cesium mobility in the environment, which is of importance in the context of geographical dispersion or concentration of the corresponding radionuclides. Among the singly charged positive clusters generated by electrospray ionization of mixtures of carboxylic acids (AH) and cesium salts (nitrate, iodide, or trifluoroacetate), the cluster [A−Cs+]Cs+[A′−Cs+] was subjected to collision-induced dissociation. The fragmentation into Cs+[A−Cs+] and Cs+[A′−Cs+] was treated using the kinetic method. A gas-phase basicity ladder was built by a step-by-step addition of the relative basicity data. The relative basicity scale deduced from the kinetic method was calibrated using the affinity and basicity (the enthalpy and Gibbs energy scales, respectively) obtained from DFT calculations. The enhanced basicity of the polyacid salts, relative to their monoacid salts, as well as the substituent effects on aliphatic and aromatic structures, are discussed. [ABSTRACT FROM AUTHOR]

Abstract: This review focuses on the quantitative data related to cesium cation interaction with neutral or negatively charged ligands. The techniques used for measuring the cesium cation affinity (enthalpies, CCA), and cesium cation basicities (Gibbs free energies, CCB) are briefly described. The quantum chemical calculations methods that were specifically designed for the determination of cesium cation adduct structures and the energetic aspects of the interaction are discussed. The experimental results, obtained essentially from mass spectrometry techniques, and complemented by thermochemical data, are tabulated and commented. In particular, the correlations between cesium cation affinities and lithium cation affinities for the various kinds of ligands (rare gases, polyatomic neutral molecules, among them aromatic compounds and negative ions) serve as a basis for the interpretation of the diverse electrostatic modes of interaction. A brief account of some recent analytical applications of ion/molecule reactions with Cs+, as well as other cationization approaches by Cs+, is given. [Copyright &y& Elsevier]

The lithium-cation basicity (LCB=Gibbs energy of adduct dissociation) of methyl benzoate, and the three isomeric dimethyl phthalates (phthalate, iso- and tere-phthalate) has been determined by Fourier transform ion cyclotron resonance (FT-ICR), using the kinetic method. The dimethyl phthalate ester appears to be a relatively strong base toward Li+, as compared to the other isomers and to methyl benzoate. This is attributed to the chelation effect of the two carboxyl groups. The previously unknown protonic gas-phase basicity of dimethyl phthalate was also determined. Chelation makes also dimethyl phthalate a much stronger base than the two other isomers toward H+, but its protonated form decomposes readily by loss of a methanol molecule. [Copyright &y& Elsevier]

The article presents an experiment that illustrates the possibilities offered by mass spectrometry for the determination of thermo-chemical data on gas-phase species. It provides students the opportunity to identify and manipulate metal-cation adducts which are frequently observed in mass spectrometry. The use of mass spectrometry to measure gas-phase basicities relative to the lithium cation is described.

The relative Lewis basicity of a series of phosphoryl compounds toward cations Mn+(OTf)n−1derived from triflate salts, M(OTf)n, is ranked using electrospray mass spectrometry according to competitive adduct formation. [ABSTRACT FROM AUTHOR]

Humic substances (HS), including humic and fulvic acids, play a significant role in the fate of metals in soils. The interaction of metal cations with HS occurs predominantly through the ionized (anionic) acidic functions. In the context of the effect of HS on transport of radioactive cesium isotopes in soils, a study of the interaction between the cesium cation and model carboxylic acids was undertaken. Structure and energetics of the adducts formed between Cs+ and cesium carboxylate salts [Cs+RCOO−] were studied by the kinetic method and density functional theory (DFT). Clusters generated by electrospray ionization mass spectrometry from mixtures of a cesium salt (nitrate, iodide, trifluoroacetate) and carboxylic acids were quantitatively studied by CID. By combining the results of the kinetic method and the energetic data from DFT calculations, a scale of cesium cation affinity, CsCA, was built for 33 cesium carboxylates representing the first scale of cation affinity of molecular salts. The structural effects on the CsCA values are discussed. [Copyright &y& Elsevier]