Gas Chromatographic-Ion Trap Mass Spectrometric Analysis of Volatile Organic Compounds by Ion–Molecule Reactions Using the Electron-Deficient Reagent Ion CCl<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack>

When using tetrachloromethane as the reagent gas in gas chromatography-ion trap mass spectrometry equipped with hybrid ionization source, the cation CCl₃⁺ was generated in high abundance and further gas-phase experiments showed that such an electron-deficient reagent ion CCl₃⁺ could undergo interesting ion–molecule reactions with various volatile organic compounds, which not only present some informative gas-phase reactions, but also facilitate qualitative analysis of diverse volatile compounds by providing unique mass spectral data that are characteristic of particular chemical structures. The ion–molecule reactions of the reagent ion CCl₃⁺ with different types of compounds were studied, and results showed that such reactions could give rise to structurally diagnostic ions, such as [M + CCl₃ – HCl]⁺ for aromatic hydrocarbons, [M – OH]⁺ for saturated cyclic ether, ketone, and alcoholic compounds, [M – H]⁺ ion for monoterpenes, M^·+ for sesquiterpenes, [M – CH₃CO]⁺ for esters, as well as the further fragment ions. The mechanisms of ion–molecule reactions of aromatic hydrocarbons, aliphatic ketones and alcoholic compounds with the reagent ion CCl₃⁺ were investigated and proposed according to the information provided by MS/MS experiments and theoretical calculations. Then, this method was applied to study volatile organic compounds in Dendranthema indicum var. aromaticum and 20 compounds, including monoterpenes and their oxygen-containing derivatives, aromatic hydrocarbon and sesquiterpenes were identified using such ion–molecule reactions. This study offers a perspective and an alternative tool for the analysis and identification of various volatile compounds.     

Reactions of Hf, Ta, and W with O2 and CO: Metal carbide and metal oxide cation bond energies

The reactions of Hf⁺, Ta⁺, and W⁺ with O₂ and CO are studied as a function of translational energy in a guided ion beam tandem mass spectrometer. All three reactions with O₂ form diatomic metal oxide cations in exothermic reactions that occur at the collision rate. In the CO systems, formation of both diatomic metal oxide and metal carbide cations is observed to be endothermic. The energy-dependent cross sections in the latter systems are interpreted to give 0 K bond energies (in eV) of D₀(HfC⁺) = 3.19 ± 0.03, D₀(TaC⁺) = 3.79 ± 0.04, D₀(WC⁺) = 4.76 ± 0.09, D₀(HfO⁺) = 6.91 ± 0.11, D₀(TaO⁺) = 7.10 ± 0.12, and D₀(WO⁺) = 6.77 ± 0.07. The present experimental values for TaO⁺ and WC⁺ agree well with literature thermochemistry, those for HfO⁺ and WO⁺ refine the available literature bond energies, and those for HfC⁺ and TaC⁺ are the first measurements available. The nature of the bonding in MO⁺ and MC⁺ is discussed and compared for these three metal ions and analyzed using theoretical calculations at a B3LYP/HW+/6-311+G(3df) level of theory. Bond energies for all MO⁺ and MC⁺ species are calculated using geometries calculated at this level and single point energies determined at B3LYP, CCSD, CCSD(T), QCISD, and QCISD(T) levels of theory with the same basis set. Reasonable agreement between the theoretical and experimental bond energies for the three metal oxide and three metal carbide cations is found. Potential energy surfaces for reaction of the metal cations with CO are also calculated at the B3LYP level of theory and reveal additional information about the reaction mechanisms.     

phosphate hydrate complexes of singly and doubly charged magnesium ions: Structure,energies, and spin states

For mixed magnesium phosphate hydrate complexes containing Mg²⁺ and Mg⁺ cations and HPO₄²⁻, HPO₄⁻, and H₂P₂O₇²⁻ anions, theoretical analysis of the electronic structure and energies has been performed at the model level in order to predict the actual role of these systems in various reactions that occur in the catalytic sites of ATP synthesizing enzymes. The calculations (DFT/B3LYP, MP2 with the 6–31G* basis set) of isolated aqua complexes Mg(H₂O) _n ^p (n = 1−6, p = 0, +1, +2) show that their relative stability monotonically increases with increasing n in each series and sharply decreases at a given n in going from the charged systems of Mg²⁺ (4–16 eV) and Mg⁺ (2–7 eV) to the neutral systems of Mg (<2 eV). An even higher stability is predicted for mixed magnesium complexes. The energies of fragmentation of mixed Mg²⁺ complexes into singlet phosphate and Mg²⁺-containing fragments at n = 0–4 are within 6–27 eV, and the energies of fragmentation into the corresponding radical ions are within 3–10 eV; for the Mg⁺ complexes, the fragmentation energies are also high (6–14 eV). The reasons for the enhanced stability of the complexes of both types have been analyzed with allowance for the predicted specific features of the electron density redistribution upon complex formation. Typical changes in the geometry of the P- and Mg-containing fragments caused by formation of mixed complexes have been discussed in the framework of the vibronic model of heteroligand systems. The high stability of all mixed magnesium complexes relative to various fragmentation products presumably rules out any dissociative processes in them in the course of ATP synthesis with the participation of phosphorylating enzymes.     

Statistical evaluations of single-ion Gibbs energies of transfer

A statistical approach for the evaluation of single-ion Gibbs energies of transfer of the cations Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ba²⁺, Ag⁺, Tl⁺, Cu⁺, Zn²⁺, Cu²⁺, Cd²⁺, Hg²⁺ and Pb²⁺ into 40 solvents based on the principal component analysis is presented. It is shown that the Gibbs energies of transfer depend both on the nature of the cation and on the donor site of the respective solvent molecule. Correlation of the data for the investigated cations required separating the solvents into subgroups according to their donor atoms in the solvent molecule. Gibbs energies of transfer into oxygen donor solvents could be correlated with the Born term [N _L(z _i e ₀)²/(8πε₀ r _i )]. Several cation parameters were investigated with respect to the transfer data into nitrogen and sulfur donor solvents. No correlations were found. Thus the use of cation parameters derived from the statistical analysis are proposed to account for the Gibbs energies of transfer into nitrogen and sulfur donor solvents. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 1, pp. 9–17. The text was submitted by the authors in English.     

Dual-level direct dynamics studies on the hydrogen abstraction reactions of fluorine atoms with CF<Subscript>3</Subscript>CH<Subscript>2</Subscript>X(X=F,Cl)

The kinetic properties of the hydrogen abstraction reactions of CF₃CH₂F + F → CF₃CHF + HF (R1) and CF₃CH₂Cl + F → CF₃CHCl + HF (R2) have been studied by dual-level direct dynamics method. Optimized geometries and frequencies of all the stationary points and extra points along the minimum-energy path (MEP) were obtained at the B3LYP/6-311 + G(2d,2p) level. Two complexes with energies less than that of the reactants were located in the reactant side of each reaction. The energy profiles were further refined with the interpolated single-point energies (ISPE) method at the G3(MP2) level of theory. Using canonical variational transition state theory (CVT) with the small-curvature tunneling correction (SCT) method, the rate constants were evaluated over a wide temperature range of 200–2,000 K. Our calculations have shown that C–H bond activity decreases when one hydrogen atom of CF₃CH₃ is substituted by a fluorine atom, than when substituted with a chlorine atom. This is in good agreement with the experimental results.     

Novel C<Subscript>β</Subscript>–C<Subscript>γ</Subscript> Bond Cleavages of Tryptophan-Containing Peptide Radical Cations

In this study, we observed unprecedented cleavages of the C_β–C_γ bonds of tryptophan residue side chains in a series of hydrogen-deficient tryptophan-containing peptide radical cations (M^•+) during low-energy collision-induced dissociation (CID). We used CID experiments and theoretical density functional theory (DFT) calculations to study the mechanism of this bond cleavage, which forms [M – 116]⁺ ions. The formation of an α-carbon radical intermediate at the tryptophan residue for the subsequent C_β–C_γ bond cleavage is analogous to that occurring at leucine residues, producing the same product ions; this hypothesis was supported by the identical product ion spectra of [LGGGH – 43]⁺ and [WGGGH – 116]⁺, obtained from the CID of [LGGGH]^•+ and [WGGGH]^•+, respectively. Elimination of the neutral 116-Da radical requires inevitable dehydrogenation of the indole nitrogen atom, leaving the radical centered formally on the indole nitrogen atom ([Ind]^•-2), in agreement with the CID data for [WGGGH]^•+ and [W_1-CH3GGGH]^•+; replacing the tryptophan residue with a 1-methyltryptophan residue results in a change of the base peak from that arising from a neutral radical loss (116 Da) to that arising from a molecule loss (131 Da), both originating from C_β–C_γ bond cleavage. Hydrogen atom transfer or proton transfer to the γ-carbon atom of the tryptophan residue weakens the C_β–C_γ bond and, therefore, decreases the dissociation energy barrier dramatically.     

Syntheses,molecular structures and magnetic properties of two hybrid organic–inorganic salts of bis(maleonitriledithiolato)copper(II) and substituted benzyl-4-dimethylaminopyridinium cations

Two new hybrid organic–inorganic salts, [BzDMAP]₂[Cu(mnt)₂](1) and [NO₂BzDMAP]₂[Cu(mnt)₂] (2) ([BzDMAP]⁺ = 1-benzyl-4′-dimethylaminopyridinium, [NO₂BzDMAP]⁺ = 1-(4′-nitrobenzyl)-4′-dimethylaminopyridinium, and mnt²⁻ = maleonitriledithiolate) have been characterized structurally and magnetically. The [BzDMAP]⁺ or [NO₂BzDMAP]⁺ cations (C) and the [Cu(mnt)₂]²⁻ anions (A) in 1 and 2 stack into a 1D alternating CC-A-CC-A-CC column. The Cu···N, π···π, C–H···N, C–H···O, and C–H···S weak interactions play important roles in the molecular stacking and generate a 2D or 3D structure of 1 and 2. The magnetic susceptibilities of these salts measured in the temperature range 2.0–300 K show weak antiferromagnetic coupling features with θ = −2.370 K for 1 and −0.222 K for 2.     

Quantum chemical analysis of possible fragmentation of [M + H]<Superscript>+</Superscript> and [M + Na]<Superscript>+</Superscript> complexes of monosubstituted methane,cyclohexane, and benzene derivatives in mass spectrometric studies

The formation and fragmentation energies of the proton and sodium cation complexes with monosubstituted methane, cyclohexane, and benzene derivatives in which carbon atoms are bonded to substituents (NH₂, OH, F, Cl, Br, ONO₂, NO₂, COOH, CN, and Ph) were calculated by the B3LYP/6-31G(d) method. For [M + Na]⁺ complexes, the formation energies are much lower (and differ from one another to a much lesser extent), while the dissociation energies are much higher, than the corresponding energies of the [M + H]⁺ complexes. Na⁺ cation shows a lower selectivity toward localization at functional groups in molecules compared to H⁺. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 246–249, February, 2008.     

Force field studies of some trifluoromethyl- and trichloromethyl-mercury-II) compounds

Force constants of [Hg(CF₃)₂], [Hg(CCl₃)₂], [Hg(CF₃)X] (X = Cl, Br, or I) and [Hg(CCl₃)X] (X = Cl or Br) have been calculated using a valence force field and wavenumber data from solutions. The potential energy distributions show substantial mixing between the symmetrical stretching and umbrella deformation coordinates of the trihalomethyl groups. The high degree of mixing of HgC and HgX stretching coordinates in [Hg(CF₃)Br] and [Hg(CF₃)I] accounts for the discontinuous frequency and intensity trends in the [Hg(CF₃)X] series.The results are discussed in comparison with methylmercury and other trifluoromethyl systems.     

Sequential bond energies of water to sodium glycine cation

Absolute bond dissociation energies of water to sodium glycine cations and glycine to hydrated sodium cations are determined experimentally by competitive collision-induced dissociation (CID) of Na⁺Gly(H₂O)_x, x = 1–4, with xenon in a guided ion beam tandem mass spectrometer. The cross sections for CID are analyzed to account for unimolecular decay rates, internal energy of reactant ions, multiple ion–molecule collisions, and competition between reaction channels. Experimental results show that the binding energies of water and glycine to the complexes decrease monotonically with increasing number of water molecules. Ab initio calculations at four different levels show good agreement with the experimental bond energies of water to Na⁺Gly(H₂O)_x, x = 0–3, and glycine to Na⁺(H₂O), whereas the bond energies of glycine to Na⁺(H₂O)_x, x = 2–4, are systematically higher than the experimental values. These discrepancies may provide some evidence that these Na⁺Gly(H₂O)_x complexes are trapped in excited state conformers. Both experimental and theoretical results indicate that the sodiated glycine complexes are in their nonzwitterionic forms when solvated by up to four water molecules. The primary binding site for Na⁺ changes from chelation at the amino nitrogen and carbonyl oxygen of glycine for x = 0 and 1 to binding at the C terminus of glycine for x = 2–4. The present characterization of the structures upon sequential hydration indicates that the stability of the zwitterionic form of amino acids in solution is a consequence of being able to solvate all charge centers.     

Molecular fragmentation on collision with protons for freon and propane molecules

In ab initio calculations, we determined the most probable routes of decomposition of the [CF₃Cl]⁺, [CF₂Cl₂]⁺, [CFCl₃]⁺, [CCl₄]⁺ molecular ions of freons and [C₃H₈]⁺ ions of hydrocarbons formed by collision of neutral molecules with protons with energies of the order of 10 keV. The calculated potential surface sections are compared on a qualitative level with the probability of various ion fragments in experiments on fragmentation. The role of the charge transfer dynamics between the proton and the molecule is discussed.     

Reactions of [Cp*Ru(H<Subscript>2</Subscript>O)(NBD)]<Superscript>+</Superscript> with diynes

Abstract  Formal [2 + 2 + 2] addition reaction of [Cp*Ru(H₂O)(NBD)][BF₄] (NBD = norbornadiene) with 4,4′-Diethynylbiphenyl generates [C₉H₉-η⁶-C₆H₄(RuCp*)–C₆H₄(RuCp*)-η⁶-C₉H₉][BF₄]₂. The reaction of [Cp*Ru(H₂O)(NBD)][BF₄] with 1,4-diphenylbutadiyne generates the unusual [2 + 2 + 2] additional organic compound Ph–C≡C–C₉H₈–Ph in addition to the organometallic compound [Cp*Ru(η⁶-C₆H₅–C≡C–C≡C–Ph)][BF₄]. [C₉H₉-η⁶-C₆H₄(RuCp*)–C₆H₄(RuCp*)-η⁶-C₉H₉][BPh₄]₂ is generated after the reaction of compound [C₉H₉-η⁶-C₆H₄(RuCp*)–C₆H₄(RuCp*)-η⁶-C₉H₉][BF₄]₂ with Na[BPh₄]. The structure of this compound was confirmed by X-ray diffraction. A possible approach to form Ph–C≡C–C₉H₈–Ph and [Cp*Ru(η⁶-C₆H₅–C≡C–C≡C–Ph)][BF₄] is suggested. Graphical Abstract  Formal [2 + 2 + 2] addition reaction of [Cp*Ru(H₂O)(NBD)]BF₄ (NBD = norbornadiene) with 4,4′-Diethynylbiphenyl generates [C₉H₉-η⁶-C₆H₄(RuCp*)–C₆H₄(RuCp*)-η⁶-C₉H₉][BF₄]₂. The reaction of [Cp*Ru(H₂O)(NBD)][BF₄] with 1,4-diphenylbutadiyne simply generates unusual [2 + 2 + 2] additional organic compound Ph–C≡C–C₉H₈–Ph in addition to the organometallic compound [Cp*Ru(η⁶-C₆H₅–C≡C–C≡C–Ph)][BF₄]. [C₉H₉-η⁶-C₆H₄(RuCp*)–C₆H₄(RuCp*)-η⁶-C₉H₉][BPh₄]₂ is generated after the reaction of compound [C₉H₉-η⁶-C₆H₄(RuCp*)–C₆H₄(RuCp*)-η⁶-C₉H₉][BF₄]₂ with Na[BPh₄]. The structure of this compound was confirmed by X-ray diffraction. And the possible approach to form Ph–C≡C–C₉H₈–Ph and [Cp*Ru(η⁶-C₆H₅–C≡C–C≡C–Ph)][BF₄] was suggested. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis,spectroscopic properties,crystal structure and biological activities of copper(II) 2-methylthionicotinate complexes with furopyridines

The synthesis and characterization of six new 2-methylthionicotinate (2-MeSnic) copper(II) monomeric complexes [Cu(2-MeSnic)₂L₂] (L is furo[3,2-c]pyridine—fpy, 2-methylfuro[3,2-c]pyridine—Mefpy, 2,3-dimethylfuro[3,2-c]pyridine—Me₂fpy or benzo[4,5]furo[3,2-c]pyridine—Bfp), [Cu(2-MeSnic)₂(fpy)₂(H₂O)], as well as [Cu(2-MeSnic)₂(CF₃Phfpy)₂(H₂O)₂] (CF₃Phfpy is 2-(3-trifluoromethylphenyl)furo[3,2-c]pyridine) are reported. The characterizations were based on elemental analysis, infrared, electronic and EPR spectra. The crystal structure of one of the complexes has been determined. The Cu^II atoms of [Cu(2-MeSnic)₂(fpy)₂(H₂O)] are six-coordinated in a highly distorted tetragonal–bipyramidal arrangement by two nitrogen atoms, one from each fpy, in trans-positions, by three oxygen atoms of the carboxyl groups of 2-MeSnic ligands (one monodentate, one asymmetrically bidentate), one axial position being occupied by the oxygen of a water molecule. The antimicrobial effects have been tested on various strains of bacteria, yeasts and filamentous fungi. A comparison of the IC₅₀ and MIC values has shown a decrease of inhibition activities of tested compounds in the order: [Cu(2-MeSnic)₂(Bfp)₂] > Bfp > [Cu(2-MeSnic)₂(CF₃Phfpy)₂(H₂O)₂] > [Cu(2-MeSnic)₂(Me₂fpy)₂] > CF₃Phfpy > [Cu(2-MeSnic)₂(Mefpy)₂] > Me₂fpy > [Cu(2-MeSnic)₂(fpy)₂(H₂O)] > [Cu(2-MeSnic)₂(H₂O)]₂ > Mefpy > fpy = 2-MeSnicH = CuSO₄. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A theoretical study on the structure,internal rotation and heat of formation of the protonated fluoroform cation (CF3H2+)

Ab initio calculations have been performed to examine the properties of the protonated fluoroform cation (CF₃H₂⁺). These calculations show that the global minimum for CF₃H₂⁺ is [CF₂H … FH]⁺ among three possible configurational isomers. This isomer is suggested to be an ion-dipole complex between CF₂H⁺ and FH. The barrier to internal rotation of the bond between carbon of CF₂H⁺ and fluorine of HF is calculated as 0.96 kcal mol⁻¹ at the MP2/6-31G(d,p) level of theory. The heat of formation of CF₃H₂⁺ at 298.15 K is estimated to be 60.6 kcal mol⁻¹ from the G2 calculation.     

Experimentally determined and calculated values of the energies required to form doubly charged ions of the bromomethanes CH3Br,CH2Br2 and CHBr3

Two experimental techniques were used to determine the double ionization energies of CH₃Br, CH₂Br₂ and CHBr₃. In one, these energies were measured directly by double-charge-transfer spectroscopy. In the other, charge stripping of [CH₃Br]⁺, [CH₂Br₂]⁺ and [CHBr₃]⁺ ions was investigated and the ionization energies of the singly charged ions were measured. The double ionization energies of the molecules obtained by adding known single ionization energies of the molecules to the single ionization energies of the ions were in good agreement with those determined by double-charge-transfer spectroscopy. The relevant mean values from the two techniques were 28.9 ± 0.5, 27.5 ± 0.5 and 29.1 ± 0.5 eV for the double ionization energy of CH₃Br, CH₂Br₂ and CHBr₃, respectively. The results of ab initio calculations using second-order Møller-Plesset perturbation theory were in good agreement with the observed double ionization energies; they were consistently slightly lower than the experimental values.     

Theoretical Study of Sticking Processes on Molecular Models of Silica Surfaces

The adsorption of small charged and neutral molecules on silica supports was modelled using perturbative post-Hartree–Fock quantum chemical methods (MP2 and MP4). The simplest spherosiloxane compound (H₄Si₄O₆) was used to mimic the surface while several molecules (namely CH₄, NH ₄ ⁺ , NH₃, OH ₃ ⁺ H ₃ ⁺ ) were considered as adsorbed species. Direct sticking of the molecules on one of the (Si–O)₃ ring leads to very different binding energies for cations (more than 11 kcal/mol) and neutral molecules (a few kcal/mol). These results indicate a dominant strong ion–multipole interaction for the first ones and a weak dispersion-type interaction for the latter. If the spherosiloxane cluster is screened by a mantle of accreted dust as it is the case in interstellar environment, the value of the binding energies, computed using the continuum dielectric theory, are predicted to be significantly reduced.     

Host–guest complexes of mixed glycol-phenanthroline cryptands: prediction of ion selectivity by quantum chemical calculations IV

Abstract Structures and complex-formation energies, calculated with DFT (B3LYP/LANL2DZp) for the cryptands [2.2.phen] and [2.phen.phen] with endohedrally complexed alkali and alkaline earth metal ions, were utilized to predict their ion selectivity. Both cryptands [2.2.phen] and [2.phen.phen] have a cavity size smaller than [2.2.2], [phen.phen.phen] and [bpy.bpy.bpy], and prefer to bind K⁺ and Sr²⁺, whereas [2.2.phen] that is larger than [2.phen.phen], has a preference for Ba²⁺, and [2.phen.phen] favours Na⁺ and Ca²⁺. The cryptand flexibility is mainly attributed to the presence of CH₂–N_SP3···N_SP3–CH₂ groups. Graphical abstract Host–Guest Complexes of mixed Glycol-Phenanthroline Cryptands—Prediction of Ion Selectivity by Quantum Chemical Calculations III Ralph Puchta* and Rudi van Eldik Keywords Cation selectivity Host–guest DFT DFT-studies allow a sensitive analysis of selectivity and cage size. Calculations predict a favourable binding of K⁺, Sr²⁺ and Ba²⁺ by [2.2.phen], and binding of K⁺, Na⁺, Ca²⁺ and Sr²⁺ by [2.phen.phen]. The cryptands fold around the ions by twisting their torsion angles in order to reach the best coordination mode for each cation. For “Prediction of ion selectivity by quantum chemical calculations III” see, R. Puchta, R. van Eldik. Aust. J. Chem. 60, 889–897 (2007).     

Atmospheric chemistry of CCl2FCH2CF3 (HCFC-234fb): Kinetics and mechanism of reactions with Cl atoms and OH radicals

The atmospheric chemistry of CCl₂FCH₂CF₃ (HFCF-234fb) was examined using FT-IR/relative-rate methods. Hydroxyl radical and chlorine atom rate coefficients of k(CCl₂FCH₂CF₃+OH)= (2.9 ± 0.8) × 10⁻¹⁵ cm³ molecule^–1 s^–1 and k(CCl₂FCH₂CF₃+Cl)= (2.3 ± 0.6) × 10⁻¹⁷ cm³ molecule^–1 s^–1 were determined at 297 ± 2 K. The OH rate coefficient determined here is two times higher than the previous literature value. The atmospheric lifetime for CCl₂FCH₂CF₃ with respect to reaction with OH radicals is approximately 21 years using the OH rate coefficient determined in this work, estimated Arrhenius parameters and scaling it to the atmospheric lifetime of CH₃CCl₃. The chlorine atom initiated oxidation of CCl₂FCH₂CF₃ gives C(O)F₂ and C(O)ClF as stable secondary products. The halogenated carbon balance is close to 80% in our system. The integrated IR absorption cross-section for CCl₂FCH₂CF₃ is 1.87 × 10⁻¹⁶ cm molecule⁻¹ (600–1600 cm⁻¹) and the radiative efficiency was calculated to 0.26 W m⁻² ppb¹. A 100-year Global Warming Potential (GWP) of 1460 was determined, accounting for an estimated stratospheric lifetime of 58 years and using a lifetime-corrected radiative efficiency estimation.     

Mössbauer spectroscopic studies on the products of [2]ferrocenophane with CF3COOH,CCl3COOH,CF3SO3H,CH3COOH and SbCl5

Reaction products of [2]ferrocenophane with CF₃COOH, CCl₃COOH, CF₃SO₃H and SbCl₅ were prepared. Mössbauer spectroscopic data and magnetic susceptibility measurements suggest the bond formation of Fe–H⁺ and Fe–Cl⁺, in which iron atoms are in a high-spin Fe/II/state.     

A theoretical study of cation--π interactions: Li+, Na+, K+, Be2+, Mg2+ and Ca2+ complexation with mono- and bicyclic ring-fused benzene derivatives

DFT (B3LYP functional) and MP2 methods using 6-311+G(2d,2p) basis set have been employed to examine the effect of ring fusion to benzene on the cation--π interactions involving alkali metal ions (Li⁺, Na⁺, and K⁺) and alkaline earth metal ions (Be²⁺, Mg²⁺ and Ca²⁺). Our present study indicates that modification of benzene (π-electron source) by fusion of monocyclic or bicyclic (or mixture of these two kinds of rings) strengthens the binding affinity of both alkali and alkaline earth metal cations. The strength of interaction decreases in the following order: Be²⁺ > Mg²⁺ > Ca²⁺ > Li⁺ > Na⁺ > K⁺ for any considered aromatic ligand. The interaction energies for the complexes formed by divalent cations are 4–6 times larger than those for the complexes involving monovalent cations. The structural changes in the ring wherein metal ion binds are examined. The distance between ring centroid and the metal ion is calculated for all of the complexes. Strained bicyclo[2.1.1]hexene ring fusion has substantially larger effect on the strength of cation--π interactions than the monocyclic ring fusion for all of the cations due to the π-electron localization at the central benzene ring.