Equilibria of aqueous solutions of isopolyniobotungstates-6 with c Nb : c W = 1 : 5

Complex formation in the Nb₆O ₁₉ ^8? -WO ₄ ^2? -H⁺-H₂O system with c _Nb : c _W = 1 : 5 and varied c _{Nb + W} ⁰ = 10^?2, 5 × 10^?3, 2.5 × 10^?3, and 10^?3 mol/L) has been studied. Distribution diagrams were simulated for individual niobium(V) and tungsten(VI) isopolyanions and mixed isopolyniobotungstates for $Z = \frac{{c_{H^ + }^0 }}{{c_{Nb + W}^0 }} = 0 - 3.0$ in an NaCl background electrolyte. We have shown that isopolyniobotungstates-6 of composition H _x NbW₅O ₁₉ ^{(3 ? x)?} are formed via H _x Nb _n W_6?n O ₁₉ ^{(2 + n ? x)?} (n=2, 3, 5) ions. The concentration formation constants and thermodynamic formation constants of isopolyniobotungstate anions (IPNTAs) in aqueous solution have been calculated. Salt Tl₃NbW₅O₁₉·9H₂O has been synthesized and identified by chemical analysis and IR spectroscopy.     

Niobium-chloride octahedral clusters as building units for larger frameworks

A systematic theoretic study on clusters containing edge-bridged octahedral metal units [Nb₆Cl₁₂] ⁿ (n?=?2, 3, or 4) and a large variety of ligands has been performed. The benchmark results on the [Nb₆Cl ₁₂ ⁱ ] ⁿ⁺ and [Nb₆Cl ₁₂ ⁱ Cl ₆ ^a ] ⁿ (n?=?2, 3 or 4) cluster units demonstrated the reliability of GGA PBE functional in combination with ZORA TZP basis set for the Nb-containing coordination compounds. The geometrical, electronic, and vibrational properties of large variety of substituted Nb₆Cl ₁₂ ⁱ Y ₆ ^a clusters have been provided. One- and two-dimensional structures with a [Nb₆Cl ₁₂ ⁱ (Bipyr) _x Cl _6?x ^a ] (x?=?2 and 4) building blocks have been proposed as good and stable candidates for new coordination polydimensional materials.     

The oxidation of chlorine ions under the joint action of ozone and permanganate ions

The oxidation of chlorine ions in the system O₃ + MnO ₄ ^? + H⁺ + Cl^? with the formation of Cl₂ in the gas phase was studied. The phenomenon of transfer catalysis of the reaction between O₃ and Cl^? by the MnO ₄ ^? ion was observed (the products of the reduction of MnO ₄ ^? by the chlorine ion are oxidized by ozone to recover MnO ₄ ^? ). The rate of the formation of Cl₂ in the O₃ + MnO ₄ ^? + H⁺ + Cl^? system was higher than the sum of the corresponding rates in the oxidation of Cl^? by O₃ and MnO ₄ ^? separately. A scheme explaining the trends observed experimentally for the formation of Cl₂ and changes in MnO ₄ ^? concentration was suggested. The formation of MnO ₄ ^? in the oxidation of Mn³⁺ with ozone in acid media was studied.     

Auftrennung von gemischten Hexa(bromochloro)-rhenaten(IV) und -osmaten(IV) auf Dünnschichtcelluloseplatten

The ions ReBr_nCl _6?n ^2? (0?n?6) and OsBr_nCl _6?n ^2? , respectively, ReO₄ ^? and Br^? have been separated on cellulose using the thin-layer chromatographic technique with 3.2 M sulphuric acid as the mobile phase.     

Group VB transition metal oxide clusters M4O n −/0 (M = Nb, Ta; n = 8–11): structural evolution and chemical bonding

The structural and electronic properties of two series of Group VB transition metal oxide clusters, M₄O _n ^? and M₄O _n (M = Nb, Ta; n = 8–11), are investigated using density functional theory calculations. Generalized Koopmans’ theorem is applied to predict the vertical detachment energies and simulate the photoelectron spectra. Large highest occupied molecular orbital–lowest unoccupied molecular orbital gaps are observed for these two stoichiometric M₄O₁₀ clusters and estimated to be 3.98 and 4.38 eV for M = Nb and Ta, respectively. The M₄O ₁₀ ^?/0 (M = Nb, Ta) clusters are polyhedral cage structures with high symmetry (T _d for the neutral and D _2d for the anion) in which each metal atom joints three bridging and one terminal O atoms. For the Nb oxide species, Nb₄O ₈ ^?/0 and Nb₄O ₉ ^?/0 can be viewed as removing two and one terminal O atoms from Nb₄O ₁₀ ^?/0 , respectively. The Ta species follow the same rule to the Nb species, except that the anionic Ta₄O₈ ^? is formed by removing one terminal and one bridging O atoms from Ta₄O₁₀ ^?. The Ta₄O₉ containing a localized Ta³⁺ site can readily react with O₂ to form the Ta₄O₁₁ which can also be viewed as replacing a terminal oxygen atom in Ta₄O₁₀ by a peroxo O₂ unit, whereas the added oxygen atom is found to be a bridging one in the O-rich clusters Nb₄O ₁₁ ^?/0 and the anionic Ta₄O₁₁ ^?. Molecular orbital analyses are performed to analyze the chemical bonding in the tetra-nuclear metal oxide clusters and to elucidate their structural and electronic evolution.     

Ln2Cl 7 − ions (Ln = La and Lu): Structures and thermodynamic stability

The equilibrium geometrical parameters and frequencies of the normal vibrations of Ln₂Cl ₇ ^? ions (Ln = La and Lu) and the enthalpies of the dissociation reactions Ln₂Cl ₇ ^? → Ln₂Cl₆ + Cl^? and Ln₂Cl ₇ ^? → LnCl₃ + LnCl ₄ ^? were calculated at the MP2 and MP4 levels (with regard to single, double, triple, and quadruple perturbations). The basis set superposition errors were eliminated by using the counterpoise approach. The potential energy surface of the Ln₂Cl ₇ ^? ions was found to reach a minimum for a configuration with three bridging and four terminal Cl atoms (symmetry C ₂). The terminal fragments LnCl₂ show almost free inherent rotation. The lanthanide compression of the interatomic Ln-Cl distances differed for the bridging and terminal Ln-Cl bonds. The calculated enthalpies of dissociation of the Ln₂Cl ₇ ^? ions were compared with data from high-temperature mass spectrometry.     

Formation of negatively-charged cluster ions in thermal energy collisions with state-selected rydberg atoms

Using crossed atomic, molecular cluster, and cw laser beams in conjunction with mass spectrometric ion detection, we have obtained for the first time results for electron transfer fromstate-selected Rydberg atoms to molecular clusters. We report negative ion mass spectra for (CO₂) _k ^? (4≦k≦25) and (O₂) _k ^? (1≦k≦13) cluster ions, resulting from collisions of Ar** (nd) Rydberg atoms (12≦n≦40) with (CO₂) _m and (O₂) _m clusters at relative velocities around 830 m/s, and, for comparison, positive ion mass spectra due to Ne(3s ³ P _{2, 0}) Penning ionization. For both CO ₂ ^? and O₂-clusters, the negative and the positive ion mass spectra are very different. For (CO₂) _k ^Emphasis>/? cluster ions, the mass spectra show distinct variations with principal quantum number of the Rydberg atom, corresponding to differentn-dependences of the effective rate constant for selected cluster ions, as measured relative to the knownn-dependence for SF ₆ ^? formation in collisions with SF₆. For (O₂) _k ^? cluster ions, on the other hand, the mass spectra are almost independent ofn with ion intensities, which clearly reflect their thermochemical stabilities (O ₄ ^? as dominant species).     

Electron attachment to oxygen and oxygen/ozone clusters studied in a high-resolution crossed beams experiment

Highly monochromatized electrons (with 30 meV FWHM) are used in a crossed beams experiment to investigate electron attachment to oxygen clusters (O₂)_n at electron energies from approximately zero eV up to 2 eV. At energies close to zero the attachment cross section for the reaction (O₂)_n +e → O ₂ ^? varies inversely with the electron energy, indicative of s-wave electron capture to (O₂)_n. Peaks in the attachment cross section present at higher energies can be ascribed to vibrational levels of the oxygen anion. The vibrational spacings observed can be quantitatively accounted for. In addition electron attachment to mixed oxygen/ozone clusters has been studied in the energy range up to 4 eV. Despite the initially large excess of oxygen molecules in the neutral clusters the dominant attachment products are undissociated cluster ions (O₃) _m ^? including the O ₃ ^? monomer while oxygen cluster ions (O₂) _n ^? appear with comparatively low intensity.     

Production and stability of oxygen cluster cations and anions,revisited

Stoichiometric and non-stoichiometric, positive and negative oxygen cluster ions (n up to 70) have been produced in a crossed neutral beam/electron beam ion source. The abundance and stability of the ions formed have been analyzed with a double focussing sector field mass spectrometer in a series of experiments. Positive and negative ion mass spectra observed exhibit distinct abundance anomalies, however, at different cluster sizes. Abundance maxima and minima correlate with correspondingly small and large metastable fractions of (O₂) _n ⁺ and (O₂) _n ^? ions, respectively. (O₂) _n ⁺ ions may also lose up top=(n?1) monomers by collision induced dissociation with monotonously decreasing probability with increasingp. Metastable fractions determined for (O₂) _n ^? ions produced with appr. zero eV electrons are in general larger than those for ions produced with appr. 7 eV electrons. (O₂) _n ^? ions are also observed to decay via autodetachment, with lifetimes increasing with increasing cluster size. Finally, here we were able to prove that an apparent loss of the monomer fragment O (and higher homologues) observed in the metastable time regime is due to ordinary metastable monomer evaporation in the acceleration region. Moreover, we will also present here some new data and interpretation concerning the electron attachment cross section function for O₂ clusters.     

Pressure and isotope effects on the proton jump of the hydroxide ion at 25°C

The limiting molar conductances Λ⁰ of potassium deuteroxide KOD in D₂O and potassium hydroxide KOH in H₂O were determined at 25°C as a function of pressure to disclose the difference in the proton-jump mechanism between an OH^? (OD^?) and a H₃O⁺ (D₃O⁺) ion. The excess conductance of the OD^? ion in D₂O λ _E ^O (OD ^-), as estimated by the equation $$\lambda _E^O (OD^ - ) = \Lambda ^O (KOD/D_2 O) - \Lambda ^O (KCl/D_2 O)$$ increases a little with pressure as well as the excess conductance of the OH^? ion in H₂O $$\lambda _E^O (OH^ - ) = \Lambda ^O (KOH/H_2 O) - \Lambda ^O (KCl/H_2 O)$$ However, their rates of increase with pressure are much smaller than those of the excess deuteron and proton conductances, λ _E ^O (D ⁺) and λ _E ^O (H ⁺). With respect to the isotope effect on the excess conductance, λ _E ^O (OH ^-)/λ _E ^O (D ⁺) decreases with presure as in the case of λ _E ^O (H ⁺)/λ _E ^O (D ⁺), but the value of λ _E ^O (OH ^-)/λ _E ^O (OD ^-) itself is much larger than that of λ _E ^O (H ⁺)/λ _E ^O (D ⁺) at each pressure. These results are ascribed to the difference in the pre-rotation of water molecules, which is brought about by the difference in the intial orientation of the rotating water molecule adjacent to the OH^? (OD^?) or the H₃O⁺ (D₃O⁺) ion.     

Small silicon oxide clusters: chains and rings

We study several silicon oxide cluster series with different Si:O stoichiometries using photoelectron spectroscopy (PES) of size-selected anions: (SiO) _n ^? (n=3–5), (SiO₂) _n ^? (n =1–4), and Si(SiO₂) _n ^? (n = 2,3). The (SiO)_n clusters are shown to be closed-shell molecules and the HOMOLUMO gaps are observed from the PES spectra to decrease for larger n. These clusters are shown to have ring sturctures. Si₃O₄ is known to have a D_2d structure with two perpendicular Si₂O₂ rhombuses.The PES spectrum of Si₄O ₆ ^? is very similar to that of Si₃O ₄ ^? . It is concluded that Si₄O₆ has a similar structure with a chain of three Si₂O₂ rhombuses. The (SiO₂)_n clusters all exhibit high electron affinities and only one band is observed at 4.66 eV photon energy. These clusters are shown to have similar chain structures containing Si₂O₂ rhombuses, but the two terminal Si atoms are bonded to an extra 0 atom each. The possibility of using these clusters to provide structural models for oxygen-deficient defects in bulk silicon oxides is also discussed.     

Photoelectron spectroscopy of silicon and germanium-fluorine binary cluster anions (SinF m − , GenF m − )

Electronic properties of silicon-fluorine and germanium-fluorine cluster anions (Si_nF _m ^? n = 1–9, m = 1–3, Ge_nF _m ^? ; n =1–9, m = 1–3) were investigated by photoelectron spectroscopy using a magnetic-bottle type electron spectrometer. The binary cluster anions were generated by a laser vaporization of a silicon/germanium rod in an He carrier gas mixed with a small amount of SiF₄ or F₂ gas. Comparison between photoelectron spectra of Si_nF^?/Ge_nF^? and Sin /Gen (n = 4–9) gives the insight that the doped F atom can remove one electron from the corresponding Sin _n ^? /Ge _n ^? cluster without any serious rearrangement of Sin/Gen framework, because only the first peak of Si _n ^? /Ge _n ^? , corresponding singly occupied molecular orbital (SOMO), disappears and other successive spectral features are unchanged with the F atom doping     

Interaction of platinum and molybdophosphoric heteropoly acid under conditions of catalyst preparation for benzene oxidation to phenol with an O2-H2 gas mixture

The transformations of platinum and a heteropoly acid (HPA) in binary systems prepared from H₂PtCl₆ or H₂PtCl₄ and H₃PMo₁₂O₄₀ were studied using IR and UV-VIS spectroscopy, elemental analysis, XPS, EXAFS, TPR, and HREM. The calcination of platinum chloride with the HPA to 450°C resulted in the formation of a platinum salt of the HPA along with decomposition products (mixture I). The reduction of calcined samples containing Pt: HPA = 1: 1 with hydrogen at 300°C (mixture II) followed by exposure to air resulted in the regeneration of the HPA structure. The resulting solid samples of Pt _1?n ⁰ Pt _n ^II Cl_mO_xH_y) (H_3+p PMo _12?p ^VI Mo _p ^V O₄₀) (III) contained platinum and molybdenum in both oxidized and reduced states. The following association species were isolated from mixtures I and II by dissolving in water: [Pt _n ^II PMo₁₂O₄₀] (I _s) (n = 0.3?0.8) and [Pt _n ⁰ PMo ₁₂ ^red O₄₀] (II _s) (n ≈ 1). Under exposure to air, the solutions of I _s were stable (pH ～2), whereas Pt^met was released from II _s. After the drying of I _s, the solid association species (Pt _n ^II Cl_mO_xH_y). (H₃PMo₁₂O₄₀), where n = 0.3?0.8, m = 0.2?1, and x = 3?0, (I _solid) were obtained. The I _solid/SiO₂ supported samples were prepared by impregnating SiO₂ with a solution of I _s and drying at 100°C. Platinum metal particles of size ～20 Å and a mixed-valence association species of platinum with the HPA were observed after the reduction of I _solid/SiO₂ with hydrogen at 100–250°C. These samples were active in the gas-phase oxidation of benzene to phenol at 180°C with the use of an O₂-H₂-N₂ mixture.     

Low-energy decay pathways of doubly charged charged silver clusters Ag n 2+ n = 9–24)

The low-energy dissociation channels of mass selected silver cluster ions Ag _n ²⁺ (n = 9–24) are determined by collision induced dissociation (CID) in a Penning trap. While all clusters of the size n ≥ 17 evaporate neutral monomers, most smaller clusters undergo asymmetric fission of the form Ag _n ²⁺ → Ag _n?3 ⁺ + Ag _{3} ⁺ . However, Ag ₁₅ ²⁺ and Ag ₁₁ ²⁺ emit monomers which indicates shell or odd-even effects. The observed fragmentation pathways are different from previous reports of measurements with sputtered Ag _n ²⁺ .     

Study of ionic equilibria and computation of thermodynamic characteristics of heteropoly anion formation in GdW10O 36 9− solution

Interaction in GdW₁₀O ₃₆ ^9? -H⁺(OH^?)-H₂O system ( \(C_{GdW_{10} O_{36}^{9 - } } \) = 1 × 10^?3 mol/L) was studied by pH potentiometry at 25 ± 0.1°C, and a model that describes equilibrium processes in acid and alkaline regions was selected. Logarithms of concentrational and thermodynamic constants, values of Gibbs energy of monomeric ions reactions, and standard Gibbs energies of formation (ΔG _f ^o ) of heteropoly anions H _n GdW₁₀O ₃₆ ^(9?n)? and H _m GdW₅O ₁₈ ^(3?n)? were calculated. A series-parallel scheme of ion transitions was pro-posed, ion distribution diagrams in aqueous solutions were built, the regions of preferable anion content were found, and heteropoly salts were synthesized.     

Electron attachment to HCl clusters

Negatively charged cluster ions of hydrogen chloride are formed by electron attachment to HCl clusters, which are produced in a seeded supersonic beam traversing a sustained gas discharge. Cluster ions of (HCl) _n ^? , withn=2, and tentatively withn=3 and 4 are observed. Cluster ions like Cl _n ^? , Cl _n ^? (HCl) _m , and withAr attached to them are also seen. The relevance to radiation chemistry of HCl if briefly discussed. Atoms evaporating from the hot, thoriated tungsten filament of the glow discharge lead to clusters such as Th _n ^? and its oxides.     

Photoemission from tin and lead cluster anions

Photoelectrons from mass-identified jet-cooled tin and lead cluster anions (Sn _n ^? , Pb _n ^? ) are detached by ultraviolet laser light (hν=3.68 eV). The photoelectron energy spectra give the detachment energies of ground state cluster anions (electron affinities) as well as excitation energies of neutral clusters in the geometry of the anions. The energy spectra for Sn _n ^? are dominated by flat thresholds with ann-dependence similar to that of other group IV clusters. In contrast, for Pb _n ^? we find pronounced narrow lines close to threshold, generally followed by a 0.3–1.4 eV gap which indicates closed-shell behaviour of Pb _n ^? for nearly alln.     

The kinetics of reaction between permanganate and chlorine ions in acid solutions

The reaction between MnO ₄ ^? and Cl^? was studied in acid media at room temperature and ionic strength 1 M. The stoichiometric equation of the reaction has the form MnO ₄ ^? + 8H⁺ + 4Cl^? = Mn³⁺ + 2Cl₂ + 4H₂O. The reaction proceeds in two stages. At the first stage, permanganate ions are consumed to produce one Cl₂ molecule per MnO ₄ ^? ion. At the second stage, the second Cl₂ molecule and the final MnO ₄ ^? reduction product (trivalent manganese) are formed. The first stage is a reaction first-order in MnO ₄ ^? and second-order in H⁺ and Cl^?; its rate constant is (9.8 ± 0.6) × 10^?2l⁴/(mol⁴ min). An analysis of the literature data leads to a value of 18–20 kcal/mol for its activation energy.     

Nucleophilic assistance in methane activation by superelectrophiles with halogen-centered cationic sites

Simulation of fragments of potential energy surface for systems CH₄ + CBr ₃ ⁺ , CH₄ + CBr ₃ ⁺ AlBr ₄ ^? , CH₄ + CCl ₃ ⁺ AlCl ₄ ^? , and CH₄ + CCl ₃ ⁺ Al₂Cl ₇ ^? was performed by DFT-B3LYP and DFT-PBE methods. The important role of nucleophilic assistance in methane halogenation by these superelectrophiles was confirmed. These reactions occur with a synchronous hydride transfer from methane to the electrophile within the cyclic transition states in linear C-H-C fragment of the rings and a generation of a C-Hlg bond between the carbon atom of the arising methyl group and the halogen atom of the electrophile. The nucleophilic assistance from the unshared electron pair of this halogen atom provides the lowering of the potential barriers to methane halogenation by complexes CBr ₃ ⁺ AlBr ₄ ^? , CCl ₃ ⁺ AlCl ₄ ^? , and CCl ₃ ⁺ Al₂Cl ₇ ^? to the values of the order of 20 kcal mol^?1. These essential features of the mechanism of methane halogenation are independent of the halogen nature and are retained on going from the model electrophiles to the real ones.     

Ab initio calculation of the vertical excitation energies of small helium cluster ions

Quantum chemical ab initio calculations have been performed for the vertical excitation energies and oscillator strengths of all low-lying electronically excited states of small helium cluster ions, He _n ⁺ ,n=2, ..., 7. The geometrical structures of the ions were fixed at the equilibrium geometries of the respective ground states, for He ₄ ⁺ and He ₅ ⁺ also one alternative structure was considered. The low-lying excited states can be classified into two categories: the electronic transition can occur either within the central He ₂ ⁺ or He ₃ ⁺ unit or from the peripheral weakly bound He atoms to this unit. The latter transitions are very weak (f≈0.001), closely spaced, with vertical excitation energies of about 5.7 eV. The He ₂ ⁺ and He ₃ ⁺ units have strong transitions at 9.93 and 5.55 eV, respectively; these transitions are only slightly blue-shifted if He ₂ ⁺ or He ₃ ⁺ are placed as “chromophores” into the centre of a larger He _n ⁺ cluster. The large difference in the vertical excitation energy of the strong transition should enable an experimental decision of the question whether the cluster ions have He ₂ ⁺ or He ₃ ⁺ cores.