How do dimethyl oxalate ions CH3O-C(=O)-C(=O)-OCH 3 ·+ break in half? Loss of CH 3 · + CO2 versus CH3O-C-O·

The interesting unimolecular dissociation chemistry of dimethyl oxalate (DMO) ions, CH₃O-C(=O)-C(=O)-OCH ₃ ^·+ , has been studied by vacuum ultraviolet photoionization and tandem mass spectrometry based experiments. The measured appearance energy (AE) for the generation of CH₃O-C=O⁺ (10. 5 eV) is not compatible with a simple bond cleavage involving the cogeneration of the radical CH₃O-C=O^· whose calculated AE is 11 kcal/mol higher. However, because the CH₃O-C=O^· radical is thermodynamically less stable than its dissociation products CH₃ ^· and CO₂, by 19 kcal/mol, a two-step dissociation of ionized DMO into CH₃O-C=O⁺ + CH ₃ ^· + CO₂ is energetically feasible. Collision induced dissociative ionization experiments clearly show that low energy DMO ions dissociate into CH₃ ^· + CO₂ without the intermediacy of CH₃O-C=O^·. Experiments using a charged collision chamber further indicate that CO₂ is released first, followed by loss of CH₃ ^· and not vice versa and a mechanism is proposed. The measured AE, which we assign to the two-step process, is 8 kcal/mol higher than the calculated value. This could be due to a competitive shift caused by a prominent low energy decarbonylation reaction yielding the hydrogen bridged radical cation CH₂=O … H … O=C-OCH₃ ^·+. However, from metastable ion observations and AE measurements on deuterium labeled DMO ions, it follows that there is no competitive shift and that the elevated AE for the two-step process corresponds to the barrier for the first step, loss of CO₂. Finally, neutralization-reionization experiments on ionized DMO and CH₃O-C=O⁺ provide evidence for the existence of CH₃O-C=O^· as a kinetically stable radical.     

H2-induced CO adsorption and dissociation over Co/Al2O3 catalyst

The activation of adsorbed CO is an important step in CO hydrogenation. The results from TPSR of pre-adsorbed CO with H2 and syngas suggested that the presence of H2 increased the amount of CO adsorption and accelerated CO dissociation. The H2 was adsorbed first, and activated to form H＊ over metal sites, then reacted with carbonaceous species. The oxygen species for CO2 formation in the presence of hydrogen was mostly OH^＊, which reacted with adsorbed CO subsequently via CO^＊＋OH^＊ → CO2^＊＋H^＊; however, the direct CO dissociation was not excluded in CO hydrogenation. The dissociation of C-O bond in the presence of H2 proceeded by a concerted mechanism, which assisted the Boudourd reaction of adsorbed CO on the surface via CO^＊＋2H^＊ → CH^＊＋OH^＊. The formation of the surface species （CH） from adsorbed CO proceeded as indicated with the participation of surface hydrogen, was favored in the initial step of the Fischer-Tropsch synthesis.     

Ab initio calculations on the isomerization of alkene radical cations

Ab initio calculations on the isomerization of butene and pentene radical cations indicate that, for all classical ion structures, the lowest barrier for a rearrangement to the most stable ion structure is below the dissociation limit. Isomerizations of linear butene radical cations to the isobutene structure take place via the CH₃CC₂H₅^·+ structure, whereas in the pentene case the connection between linear and branched ion structures proceeds via the 1,2-dimethylcyclopropane radical cation. From the results a qualitative model is derived which suggests that for larger alkene radical cations an isomerization to structures with four alkyl substituents on the double bond may be in close competition with dissociation.     

Thermospray mass spectrometry of N-methylcarbamates

The thermospray mass spectrometry (TSP/MS) of five N-methylcarbamates is presented. This is the first time that ions other than [M + H]⁺ and [M + NH₄]⁺ have been reported using positive TSP/MS. Protonation of ROCONHCH₃ yields the [CH₃NH₂CO]^+· ion, with formation of the ion–molecule adduct [ROCONHCH₃ · CH₃NH₂CO]^+· through elimination of CO^+· from [CH₃NH₂CO]^+·, and the adduct [M + 75]^+·, [ROCONHCH₃ · OCONH₂CH₃]^+·, is also obtained.     

Enthalpies of formation of radicals and the mass spectra of the products of tetrafluoroethylene polymerization in acetone

The mass spectra of the dissociative electron-impact ionization products of telomers formed upon the radiation-chemical telomerization of tetrafluoroethylene in acetone were measured over the range of m/z from 1 to 204. The most intense bands at m/z = 43, 51, and 57 were attributed to the CH₃CO⁺, CF₂H⁺ and CH₃COCH₂⁺ cations—the main dissociation products of the H(C₂F₄) _n CH₂COCH₃ telomers. The telomer composition was consistent with a radical telomerization mechanism, in which chain growth and chain transfer are due to the formation of the CH₃COCH₂^· radical. Based on published data supplemented with quantum-chemical calculations, the enthalpies of formation of the radicals R(CF₂) _n (n = 2–8; R = H, CH₃, CH₃CO, and CH₃COCH₂) were tabulated. The formation of telomers with the same terminal groups is consistent with thermodynamic data and a polymerization mechanism in which the chain growth reaction is diffusion-limited and the chain transfer reaction is activated hydrogen-atom transfer.     

Probing the pyrolysis of methyl formate in the dilute gas phase by synchrotron radiation and theory

The thermal dissociation of the atmospheric constituent methyl formate was probed by coupling pyrolysis with imaging photoelectron photoion coincidence spectroscopy (iPEPICO) using synchrotron VUV radiation at the Swiss Light Source (SLS). iPEPICO allows threshold photoelectron spectra to be obtained for pyrolysis products, distinguishing isomers and separating ionic and neutral dissociation pathways. In this work, the pyrolysis products of dilute methyl formate, CH₃OC(O)H, were elucidated to be CH₃OH + CO, 2 CH₂O and CH₄ + CO₂ as in part distinct from the dissociation of the radical cation (CH₃OH^+• + CO and CH₂OH⁺ + HCO). Density functional theory, CCSD(T), and CBS-QB3 calculations were used to describe the experimentally observed reaction mechanisms, and the thermal decomposition kinetics and the competition between the reaction channels are addressed in a statistical model. One result of the theoretical model is that CH₂O formation was predicted to come directly from methyl formate at temperatures below 1200 K, while above 1800 K, it is formed primarily from the thermal decomposition of methanol.     

Kristallstrukturelle,Festkörper‐31P‐CP/MAS‐NMR,TOSS, 31P‐COSY‐NMR und mechanistische Beiträge zur Koordinationschemie des Octacarbonyldicobalts mit den Liganden Bis(diphenylphosphanyl)amin,Bis(diphenylphosphanyl)methan und 1,1,1‐Tris(diphenylphosphanyl)ethan

Chemistry of Polyfunctional Molecules. 133. X‐Ray Crystal Structural, Solid‐state ³¹P CP/MAS NMR, TOSS, ³¹P COSY NMR, and Mechanistic Contributions to the Co‐ordination Chemistry of Octacarbonyldicobalt with the Ligands Bis(diphenylphosphanyl)amine, Bis(diphenylphosphanyl)methane, and 1,1,1‐Tris(diphenylphosphanyl)ethane Co₂(CO)₈ reacts with bis(diphenylphosphanyl)amine, HN(PPh₂)₂ (Hdppa, 1 ), in two steps to afford the known compound [Co(CO)(Hdppa‐κ²P)₂][Co(CO)₄] · 2 THF ( 6 a · 2 THF). The intermediate [Co(CO)₂(Hdppa‐κ²P) · (Hdppa‐κP)][Co(CO)₄] · dioxane · n‐pentane ( 5 · dioxane · n‐pentane) was isolated for the first time and was characterized by X‐ray analysis. The cation 5 ⁺ exhibits a slightly distorted trigonal‐bipyramidal geometry. Detailed ³¹P‐NMR investigations (solid‐state CP/MAS NMR, TOSS, ³¹P‐COSY, ³¹P‐EXSY) showed that the additional tautomer [Co(CO)₂(Hdppa‐κ²P)(Ph₂P–N=P(H)Ph₂‐κP)]⁺ ( 5 ′⁺) is present in solution. The tautomer equilibrium is slow in the NMR time scale. In contrast to the solid state only tetragonal pyramidal species of 5 are found in solution. At –90 °C there is slow exchange between the three diastereomeric species 5 a ⁺– 5 c ⁺. Compound 5 forms [Co(CO) · (Hdppa‐κ²P)₂]BPh₄ · THF ( 6 b · THF) in THF with NaBPh₄ under CO‐Elimination. A X‐ray diffraction investigation shows that the cation 6 ⁺ consists of a slightly distorted trigonal‐bipyramidal co‐ordination polyeder. However, a distorted tetragonal‐pyramidal structure has been found for the cation 7 ⁺ of the related compound [Co(CO)(dppm)₂][Co(CO)₄] · 2 THF ( 7 · 2 THF; dppm = bis(diphenylphosphanyl)methane, Ph₂PCH₂PPh₂). A comparison with the known [8] trigonal‐bipyramidal stereoisomer, ascertained for 7 ⁺ of the solvent‐free 7 , is described. In solutions of 6 a · 2 THF and 7 · 2 THF ¹³C{¹H}‐ and ³¹P{¹H}‐NMR spectra indicate an exchange of all CO and organophosphane molecules between cobalt(I) cation and cobalt(–I) anion. A concerted mechanism for the exchange process is discussed. CO elimination leads to discontinuance of the cyclic mechanism by forming binuclear substitution products such as the isolated Co₂(CO)₂ · (μ‐CO)₂(μ‐dppm)₂ · 0.83 THF ( 8 · 0.83 THF), which was characterized by spectroscopy and X‐ray analysis. For the dissolved [Co(CO)₂CH₃C(CH₂PPh₂)₃][Co(CO)₄] · 0.83 n‐pentane ( 9 a · 0.83 n‐pentane) no CO and triphos exchange processes between the cation and the anion are observed. Metathesis of 9 a · 0.83 n‐pentane with NaBPh₄ yields [Co(CO)₂CH₃C(CH₂PPh₂)₃]BPh₄ ( 9 b ) which has been characterized by single‐crystal X‐ray analysis. The cation shows a small distorted tetragonal‐pyramidal structure.     

Uncommon hydrogen bonds between a non-classical ethyl cation and π hydrocarbons: a preliminary study

This study undertakes a theoretical investigation into uncommon hydrogen bonds between the ethyl cation (C₂H₅ ⁺) and π hydrocarbons. Firstly, it considers the hyperconjugation effect of the ethyl cation, in which the non-localized hydrogen (H⁺) is taken to be a pseudoatom bound to the carbons of the methyl groups. The goal of the research is to use this electronic phenomenon to gain a better understanding of the (H⁺···π) and (H⁺···p-π) hydrogen bonds, which are considered uncommon because they are formed through the interaction of the H⁺ of the ethyl cation with the π bonds of the acetylene (C₂H₂) and ethene (C₂H₄), as well as with the pseudo-π bond of the cyclopropane (C₃H₆). In view of this, B3LYP/6-311++G(d,p) calculations were used to determine the geometries of the C₂H₅ ⁺···C₂H₂, C₂H₅ ⁺···C₂H₄, and C₂H₅ ⁺···C₃H₆ hydrogen-bonded complexes. Deformations of the bond lengths and bond angles of these systems were analyzed geometrically. Examination of the stretch frequencies and absorption intensities of the (H⁺···π) and (H⁺···p-π) hydrogen bonds has revealed red-shifts in π and p-π bonds. After structural modeling and vibrational characterization, analysis of the charge transfer following the ChelpG approach and subsequently quantification of the hydrogen bond energies (basis sets superpostition error and zero point vibrational energies being considered) were used to predict the strength of the (H⁺···π) and (H⁺···p-π) hydrogen bonds. In addition, the molecular topography was estimated using the quantum theory of atoms in molecules (QTAIM). QTAIM was chosen because of a desire to understand the (H⁺···π) and (H⁺···p-π) hydrogen bonds chemically on the basis of the quantity of charge density and interpretation of Laplacian fields. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Gas-phase fragmentation of long-lived cysteine radical cations formed via no loss from protonated S-nitrosocysteine

In this work, we describe two different methods for generating protonated S-nitrosocysteine in the gas phase. The first method involves a gas-phase reaction of protonated cysteine with t-butylnitrite, while the second method uses a solution-based transnitrosylation reaction of cysteine with S-nitrosoglutathione followed by transfer of the resulting S-nitrosocysteine into the gas phase by electrospray ionization mass spectrometry (ESI-MS). Independent of the way it was formed, protonated S-nitrosocysteine readily fragments via bond homolysis to form a long-lived radical cation of cysteine (Cys^•+), which fragments under collision-induced dissociation (CID) conditions via losses in the following relative abundance order: •COOH ≫ CH₂S > •CH₂SH-H₂S. Deuterium labeling experiments were performed to study the mechanisms leading to these pathways. DFT calculations were also used to probe aspects of the fragmentation of protonated S-nitrosocysteine and the radical cation of cysteine. NO loss is found to be the lowest energy channel for the former ion, while the initially formed distonic Cys^•+ with a sulfur radical site undergoes proton and/or H atom transfer reactions that precede the losses of CH₂S, •COOH, •CH₂SH, and H₂S.     

Photoinduced electron transfer reactions in the 10-methylacridinium cation–benzyltrimethylsilane system: steady-state and flash photolysis studies

The mechanism of the photoinduced reaction of the lowest excited singlet state of the 10-methylacridinium (AcrMe⁺) cation with benzyltrimethylsilane (BTMSi) in acetonitrile has been investigated by means of steady-state and time-resolved methods. A variety of stable products was found after irradiation (365 nm) of the reaction mixture under aerobic and oxygen-free conditions. The stable products were identified and analyzed using UV–Vis spectrophotometry, high performance liquid chromatography (HPLC), and mass spectrometry (MS). Based on Stern–Volmer plots of the AcrMe⁺ fluorescence quenching by BTMSi (using fluorescence intensity and lifetime measurements), the rate constants were determined to be k _q = 1.24 (± 0.02) × 10¹⁰ M⁻¹ s⁻¹ and k _q = 1.23 (± 0.02) × 10¹⁰ M⁻¹ s⁻¹, i.e., close to the diffusion-controlled limit in acetonitrile, indicating the dynamic quenching mechanism. The quenching process was shown to occur via an electron-transfer reaction leading to the formation of acridinyl radicals (AcrMe^•) and C₆H₅CH₂Si(CH₃)₃ ^•+ radical cations. Based on stationary and flash photolysis experiments, a detailed mechanism of the secondary reactions is proposed and discussed. The AcrMe^• radical was shown to decay by two processes. The fast decay, observed on the nanosecond timescale, was attributed to the back-electron transfer occurring within the initial radical ion pair. The slow decay on the microsecond timescale was explained by recombination reactions of radicals which escaped from the radical pair, including benzyl radicals formed via C–Si bond cleavage in the C₆H₅CH₂Si(CH₃)₃ ^•+ radical cation.     

ESR study on photoreaction of formato complex of europium(III) in HCOOH-HCOONa buffer solution

Matrix isolation ESR study showed that the ligated HCCO^? ion was decomposed into H⁺ and ·COO^? radical anion through CTTM process at λ = 254 nm, by contrast, ·CH₃ radical and CO₂ were produced from CH₃COO^? ligand. In order to explain the photo- and related reactions in the liquid solution, a proposal is made for a cyclic scheme conjugated with the photo-decomposition of the complex. The cycle consists of three steps; photo-reduction of H⁺ by Eu²⁺, radical alternation from ·H to ·COO^?, and oxidation of ·COO^? by Eu³⁺.     

Free radical abstraction of H atom from peroxides with concerted dissociation of O-O bond

Quantum chemical calculations of the dissociation energy of the C-H bond in the ??-hydroperoxide fragment of Me₂CHOOH were carried out. It was shown that abstraction of H atom is accompanied by dissociation of the O-O bond. Density functional calculations of transition states of the reactions of ^·CH₃, CH₃OO^·, and HO₂ ^· radicals with the C-H bond in the ??-hydroperoxide fragment of Me₂CHOOH were carried out. It was established that H atom abstraction is accompanied by concerted dissociation of the O-O bond. For 45 peroxides R¹R²CHOOH, R¹R²CHOOR³, and R¹R²CHOOC(O)R³ (R¹, R² = H, Me, Et, Ph, H₂C=CH), the enthalpies of H atom abstraction from the C-H bond in the a-hydroperoxide fragment with fragmentation of the peroxides at the O-O bond were calculated. The kinetic parameters for 12 classes of radical abstraction reactions with fragmentation of molecules were calculated from experimental data within the framework of the model of intersecting parabolas. The activation energies and reaction rate constants of H atom abstraction from C-H bonds of a-peroxide fragments involving peroxyl and alkyl radicals were determined for 45 peroxides of different structure.     

Characterization of the C3H6O+· ion from 2-methoxyethanol. Mixture analysis by dissociation and neutralization—reionization

The C₃H₆O^+· ion formed upon the dissociative ionization of 2-methoxyethanol is identified by a combination of several tandem mass spectrometry methods, including metastable ion (MI) characteristics, collisionally activated dissociation (CAD), and neutralization—reionization mass spectrometry (NRMS). The experimental data conclusively show that 2-methoxyethanol molecular ion, namely, HOCH₂CH₂OCH ₃ ^+· , loses H₂O to yield mainly the distonic radical ion ·CH₂CH₂OCH ₂ ⁺ along with a smaller amount of ionized methyl vinyl ether, namely, CH₂=CHOCH ₃ ^+· . Ring-closed products, such as the oxetane or the propylene oxide ion are not observed. The proportion of ·CH₂CH₂OCH ₂ ⁺ increases with decreasing internal energy of the 2-methoxyethanol ion, which indicates a lower critical energy for the pathway leading to this product than for the competitive generation of CH₂=CHOCH ₃ ^+· . The present study also uses MI, CAD, and NRMS data to assess the structure of the distonic ion⁺ (CH₃)CHOCH₂· (ring-opened ionized propylene oxide) and evaluate its isomerization proclivity toward the methyl vinyl ether ion.     

Fragmentation of <Emphasis Type="Italic">α</Emphasis>-radical cations of arginine-containing peptides

Fragmentation pathways of peptide radical cations, M^+·, with well-defined initial location of the radical site were explored using collision-induced dissociation (CID) experiments. Peptide radical cations were produced by gas-phase fragmentation of Co^III(salen)-peptide complexes [salen=N,N′-ethylenebis (salicylideneiminato)]. Subsequent hydrogen abstraction from the β-carbon of the side-chain followed by C_α-C_β bond cleavage results in the loss of a neutral side chain and formation of an α-radical cation with the radical site localized on the α-carbon of the backbone. Similar CID spectra dominated by radical-driven dissociation products were obtained for a number of arginine-containing α-radicals, suggesting that for these systems radical migration precedes fragmentation. In contrast, proton-driven fragmentation dominates CID spectra of α-radicals produced via the loss of the arginine side chain. Radical-driven fragmentation of large M^+· peptide radical cations is dominated by side-chain losses, formation of even-electron a-ions and odd-electron x-ions resulting from C_α-C bond cleavages, formation of odd-electron z-ions, and loss of the N-terminal residue. In contrast, charge-driven fragmentation produces even-electron y-ions and odd-electron b-ions.     

High level ab initio and density functional theory study of bond selective dissociation of CH3SH and CH3CH2SH radical cations

Selective bond dissociation energies for CH₃SH and CH₃CH₂SH radical cations were evaluated with G1, G2, G2MP2, B3LYP, BLYP, and SVWN computational methods. It was determined that both G2 and CBSQ evaluate very accurate bond dissociation energies for thiol radical cations, while gradient-corrected BLYP computes the best energies of three employed DFT methods. For the CH₃CH₂SH radical cation, new, higher than previously estimated selective bond dissociation energies were suggested. Received: 10 September 1997 / Accepted: 9 September 1998 / Published online: 11 November 1998     

The [CH5NO]+ ˙ potential energy surface: Distonic ions,lon-dipole complexes and hydrogen-bridged radical cations

By combining results from a variety of mass spectrometric techniques (metastable ion, collisional activation, collision-induced dissociative ionization, neutralization-reionization spectrometry, ²H, ¹³C and ¹⁸O isotopic labelling and appearance energy measurements) and high-level ab initio molecular orbital calculations, the potential energy surface of the [CH₅NO]^{+ ˙} system has been explored. The calculations show that at least nine stable isomers exist. These include the conventional species [CH₃ONH₂]^{+ ˙} and [HO? CH₂? NH₂]^{+ ˙}, the distonic ions [O? CH₂? NH₃]^{+ ˙}, [O? NH₂? CH₃]^{+ ˙}, [CH₂? O(H)? NH₂]^{+ ˙}, [HO? NH₂? CH₂]^{+ ˙}, and the ion-dipole complex CH₂?NH₂⁺ …? OH˙. Surprisingly the distonic ion [CH₂? O? NH₃]^{+ ˙} was found not to be a stable species but to dissociate spontaneously to CH₂?O + NH₃^{+ ˙}. The most stable isomer is the hydrogen-bridged radical cation [H? C?O …? H …? NH₃]^{+ ˙} which is best viewed as an immonium cation interacting with the formyl dipole. The related species [CH₂?O …? H …? NH₂]^{+ ˙}, in which an ammonium radical cation interacts with the formaldehyde dipole is also a very stable ion. It is generated by loss of CO from ionized methyl carbamate, H₂N? C(?O)? OCH₃ and the proposed mechanism involves a 1,4-H shift followed by intramolecular ‘dictation’ and CO extrusion. The [CH₂?O …? H …? NH₂]^{+ ˙} product ions fragment exothermically, but via a barrier, to NH₄^{+ ˙} HCO^…? and to H₃N? C(H)?O^{+ ˙} H˙. Metastable ions [CH₃ONH₂]^+…? dissociate, via a large barrier, to CH₂?O + NH₃⁺ + and to [CH₂NH₂]⁺ + OH˙ but not to CH₂?O^{+ ˙} + NH₃. The former reaction proceeds via a 1,3-H shift after which dissociation takes place immediately. Loss of OH˙ proceeds formally via a 1,2-CH₃ shift to produce excited [O? NH₂? CH₃]^{+ ˙}, which rearranges to excited [HO? NH₂? CH₂]^{+ ˙} via a 1,3-H shift after which dissociation follows.     

Structures of decomposing and non-decomposing gas-phase [C4H6O]+· radical cations,and their [C2H2O]+· and [C3H6]+· product ions

The structures of gas-phase [C₄H₆O]^+· radical cations and their daughter ions of composition [C₂H₂O]^+· and [C₃H₆]^+· were investigated by using collisionally activated dissociation, metastable ion measurement, kinetic energy release and collisional ionization tandem mass spectrometric techniques. Electron ionization (70 eV) of ethoxyacetylene, methyl vinyl ketone, crotonaldehyde and 1-methoxyallene yields stable [C₄H₆O]^+· ions, whereas the cyclic C₄H₆O compounds undergo ring opening to stable distonic ions. The structures of [C₂H₃O]^+· ions produced by 70-eV ionization of several C₄H₆O compounds are identical with that of the ketene radical cation. The [C₃H₆]^+· ions generated from crotonaldehyde, methacrylaldehyde, and cyclopropanecarboxaldehyde have structures similar to that of the propene radical cations, whereas those ions generated from the remainder of the [C₄H₆O]^+· ions studied here produced a mixed population of cyclopropane and propene radical cations.     

Dissociative chemistry of ionic transition metal cluster fragments

The ionic fragments formed by collision-induced dissociation of Mn₂(CO) _y ⁺ ions (y=1–10) are reported. The ratio of product ions formed by metal-metal vs. metal-ligand bond cleavage are discussed in terms of the dependence of the metal-metal bond energy on the metal-to-ligand ratio. The collision-induced dissociation data indicate that the metal-metal bond energy of Mn₂(CO) ₅ ⁺ and Mn₂(CO) ₁₀ ⁺ is less than that for Mn₂(CO) _y ⁺ (y=1–4 and 6–9). The product ions arising by metal-metal and metal-ligand bond cleavage reactions for collision-induced dissociation and photodissociation are compared. On the basis of this data and the known photochemistry/photophysics of Mn₂(CO)₁₀, it is proposed that the difference in collision-induced dissociation and photodissociation product ion branching ratios is attributable to spin-orbit transitions of the activated ions.     

Nongeneral Character of the Resonance Parameters Σ<Stack><Subscript>R</Subscript><Superscript>+</Superscript></Stack> of Silicon-, Germanium-, and Tin-Containing Substituents in Radical Cations

The resonance parameters σ _R ⁺ of substituents Y in radical cations YD^+· [where D is a π- or n-type center, and Y = MMe₃, CH₂MMe₃ (M = Si, Ge, Sn), C(SiMe₃)₃] depend on the nature of both Y and D. Using radical cations YD^+· (Y = CH₂SiMe₃, SnMe₃) as examples, it was found that the two conjugation parameters, constants σ _R ⁺ of substituents Y and perturbation energy calculated by the modified molecular orbital perturbation method, are linearly related to each other. The energies of donor and acceptor components of the overall resonance effect of CH₂SiMe₃ and SnMe₃ with respect to radical cation centers D^+· were estimated for the first time. The donor energy constituent in YD^+· is considerably greater than in neutral DY molecules.     

Ionic crystals based on Keggin anion and mixed-valent diruthenium tetracetate: [Ru2(CH3COO)4(H2O)2]2[HnXW12O40]·[Ru2(CH3COO)4(H2O)Cl]·12H2O (X = B,Si, Ge)

Three new ionic crystals based on Keggin anion and mixed-valent diruthenium tetracetate, [Ru₂(CH₃CO₂)₄(H₂O)₂]₂[H_nXW₁₂O₄₀]·[Ru₂(CH₃CO₂)₄(H₂O)Cl]·12H₂O {X = B, n = 3 (1); X = Si, n = 2 (2); X = Ge, n = 2 (3)}, have been prepared in acidic aqueous solution at about pH 3.0 by reaction of K₄BW₁₂O₄₀·mH₂O, K₈SiW₁₁O₃₉·mH₂O and K₈GeW₁₁O₃₉·mH₂O with diruthenium tetracetate Ru₂(CH₃COO)₄Cl, respectively, and their structures were determined by X-Ray diffraction analysis. They are isostructural structure with the ratio of heteropolytungstate anion, Ru₂(CH₃CO₂)₄⁺ cation and neutral molecular Ru₂(CH₃CO₂)₄Cl of 1:2:1. The cyclic voltammetry in 0.5 M KNO₃ aqueous solution at pH 3.0 show the respective electrochemical behaviors of the W-centers and Ru₂-centers for these three complexes. Magnetic data analysis shows that diruthenium units display the ground state electronic configuration π*²δ* with large positive D value.