Studies on the reaction N + N3 → N2(B 3Πg) + N2(X 1Σ+g)

Strongly enhanced N₂ first positive emission N₂(B ³Π_g → A ³Σ⁺_u) has been observed on addition of N atoms into a flowing mixture of Cl and HN₃. The dependence of the emission intensity on N atom concentration gave a rate constant for the reaction N + N₃ → N₂(B ³Π_g) + N₂(X ¹Σ⁺_g) of _i(1.6 ± 1.1) × 10^?11 cm³ molecule^?1 s^?1. That for the reaction Cl + HN₃ → HCl + N₃ is (8.9 ± 1.0) × 10^?13 cm³ molecule^?1 s^?1 from the decay of the emission. Comparison of the emission intensity in ClHN₃ with that in ClHN₃N gave the rate constant of the reaction N₃ + N₃ → N₂(B ³Π_g) + 2N₂(X ¹Σ⁺_g) as 1.4 × 10^?12 cm³ molecule^?1 s^?1 on the assumption that N + N₃ yields only N₂(B ³Π_g) + N₂(X ¹Σ⁺_g).     

Laser-induced fluorescence in N2 and N+2 by multiple-photon excitation at 266 nm

The fluorescence transitions corresponding to the second positive system of N₂ (C³Π_u → B³Π_g) for Δv = 0, 1 and the first negative system of N⁺₂(B²Σ⁺_u → X²Σ⁺_g) for Δv = 0, 1, 2 have been observed following laser-induced mul excitation of N₂.     

Unusual stabilization of cationic “M(η-allyl) (M = Pt, Pd) units by a dianionic cis-{Pt(C6F5)2(CCSiMe3)2} fragment

Chloride abstraction from [{M(η³ --- C₃H₅)Cl}_n] (M = Pt, n = 4 or M = Pd, n = 2) by (NBu₄)₂[cis-Pt(C₆F₅)₂(CCSiMe₃)₂] (1) gives rise to novel homo- and hetero-dinuclear zwitterionic derivatives (NBu₄) [{cis-Pt(C₆F₅)₂(CCSiMe₃)₂}M(η³-C₃H₅)] (M = Pt 2; M = Pd 3) which are formed by a M(η³-allyl)⁺ unit attached to both alkynyl ligands of the {cis-Pt(C₆F₅)₂(CCSiMe₃)₂}²⁻ fragment. The structure of 3 has been established by X-ray diffraction.     

Nonparameterized MO calculations of ligand-bridged M2(CO)8-(U2-X)2-type dimers containing metal---metal interactions: Evidence for dictation of stereochemistry by one-electron and two-electron metal---metal σ-type bonds

Nonparameterized MO calculations performed on the (edge-bridged)-bioctahedral metal dimers of the Dessy-characterized [Cr₂(CO)₈(μ₂-PR₂)₂]^(n-2) series and of the [Mn₂(CO)₈(μ₂-PR₂)₂]ⁿ series (n = 0, +1, +2) have revealed that the corresponding dimeric pairs with n = 0, +1, and +2 have two, one, and no electrons, respectively, in the antibonding 2b_3u MO corresponding to a “net” no-electron metal---metal bond, a “net” one-electron metal---metal bond, and a two electron metal---metal bond. Of prime significance is that this 2b_3u MO, which is the LUMO in both electron-pair (metal---metal)-bonded dimers (n = +2) and the HOMO in the corresponding dimers to which one or two electrons have been added, is found to be largely composed of in-plane antibonding σ-type dimetal orbital character rather than either out-of-plane π-type dimetal antibonding orbital character or bridging-ligand orbital character. These MO results are also shown to be completely compatible with the available spectral and X-ray data.     

Cyclopentadienyl-ruthenium and -osmium chemistry : XXXIX. Syntheses of novel alkynyl-ruthenium complexes. X-Ray structures of two forms of {Ru(PPh3)2(η-C5H5)}2(μ-C4) and of Ru{CCC(O)Me}(PPh3)2(η-C5H5)

Reactions between [Ru(thf)(PPh₃)₂(η-C₅H₅)]⁺ and lithium acetylides have given further examples of substituted ethynylruthenium complexes that are useful precursors of allenylidene and cumulenylidene derivatives. From Li₂C₄, mono- and bi-nuclear ruthenium complexes were obtained: single-crystal X-ray studies have characterised two rotamers of {Ru(PPh₃)₂(η-C₅H₅)}₂(μ-C₄), which differ in the relative cis and trans orientations of the RuL_n groups. Protonation of Ru(CCCCH)(PPh₃)₂(η-C₅H₅) afforded the butatrienylidene cation [Ru(C=C=C=CH₂)(PPh₃)₂(η-C₅H₅)]⁺, which reacted readily with atmospheric moisture to give the acetylethynyl complex Ru{CCC(O)Me}(PPh₃)₂(η-C₅H₅), also fully characterised by an X-ray structural study.     

Fabrication and characterizations of mesoporous TiO2 and SiO2/TiO2 composite with high photocatalytic activity using a new Gemini surfactant

In this paper, mesoporous rod-like SiO₂/TiO₂ (m-SiO₂/TiO₂) and mesoporous sphere-like TiO₂ (m-TiO₂) have been prepared by using a new type Gemini surfactant containing carbonyl groups (GS-A, [(C _n H_{2n + 1})(CH₃)₂N⁺(CH₂)₂-O₂C-(CH₂)₄-CO₂-(CH₂)₂N⁺(CH₃)₂(C _n H_{2n + 1})] · 2Br⁻, n = 12) as template at pH ∼ 6 at room temperature. The products are characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and N₂ adsorption-desorption. The results indicate that anatase TiO₂ exists in both samples and m-SiO₂/TiO₂ has a higher surface area (741.13 m²/g) than m-TiO₂. Moreover, as-synthesized samples show excellent photocatalytic activity for the degradation of methyl red under UV irradiation.     

Collisional fragmentation of Ar@C60

The fragmentation patterns resulting from collisions between (Ar@C₆₀)⁺ or (Ar@C₆₀)⁻ ions and H₂, He, CH₄, Ne, Ar and Kr target gases have been measured. The ion-source material Ar@C₆₀ was synthesized by heating C₆₀ under 3000 atm of argon gas, leading to a 10⁻³ concentration of endohedral fullerenes. The fragmentation spectra (charged molecules only) are dominated by positive ions both when positive or negative endohedrals break up. Endohedral fragment ions Ar@C_n⁺ (48n60) as well as all carbon fragments are observed. For collisions involving (Ar@C₆₀)⁻, ejection of the Ar atom together with two electrons, without permanently damaging the fullerene cage, is a prominent reaction channel, indicating that a ‘window' or a deformation in the form of e.g. a large hole, through which the argon atoms can exit, is opened during the collision.     

Vacuum UV emission by electronically-excited N2: The radicative lifetime of the N2(a′1Σ−u state

A measurement of the electronic transition moment variation for the N₂(a'¹Σ^?_uX¹Σ^+g) band system has allowed a reassessment of the radiative lifetime of N₂(a′). Relaxation to N₂(a′,υ=0) is established as the major channel for quenching of N₂(a¹Π_g, υ = 0) molecules by Ar.     

Low-Temperature Electronic Properties of the Lan+1NinO3n+1 (n = 2, 3, and ∞) System: Evidence for a Crossover from Fluctuating-Valence to Fermi-Liquid-like Behavior

Measurements of the temperature dependence of the electrical resistivity ρ(T), magnetic susceptibility χ(T), and Seebeck coefficient S(T) have been carried out on the n = 2, 3, and ∞ members of the homologous lanthanum nickel oxide systems La_n+1Ni_nO_3n+1 that were annealed in air. With increasing n, a progressive decrease in the electrical resistivity and a gradual change from insulating to metallic behavior are observed. La₃Ni₂O₇ is nonmetallic, showing a gradual increase in ρ when T decreases (dp/dT < 0) from 300 to 4.2 K, whereas La₄Ni₃O₁₀ and LaNiO₃ exhibit metallic resistivity (dp/dT > 0). A minimum in ρ(T) near 140 K is observed for La₄Ni₃O₁₀, while LaNiO₃ exhibits a T² dependence for ρ(T) below 50 K. The magnetic susceptibility of LaNiO₃ is Pauli-like, but the χ(T) data for La₃Ni₂O₇ and La₄Ni₃O₁₀ below 350 K show a decrease with decreasing temperature. The Seebeck coefficient of all these compounds is negative at high temperatures; La₃Ni₂O₇ and La₄Ni₃O₁₀ exhibit a sign change in S at low temperatures. These results suggest a crossover from a fluctuating-valence to a Fermi-liquid-like behavior with increasing n.     

The relevancy of the [B2N4] substructure in the electronic structure of the metal-rich lanthanum nitridoborate La3(B2N4)

Lanthanoide nitridoborates of the general formula Ln₃(B₂N₄) with Ln=La, Ce, Pr, and Nd occur as black crystalline materials. Their structures contain oxalate-like [B₂N₄]⁸⁻ ions being stacked in an eclipsed formation along one crystallographic direction. Electronic structures were calculated for a molecular [B₂N₄]⁸⁻, for the [B₂N₄] partial structure, and for the complete La₃(B₂N₄) structure with the extended Hückel algorithm to analyze the bonding characteristics and to trace the necessity and properties of one surplus electron of (La³⁺)₃(B₂N₄⁸⁻)(e⁻). The HOMO of a [B₂N₄]⁸⁻ is B-B σ bonding, and the LUMO is B-B π bonding but B-N antibonding. The energy band of the solid state [B₂N₄] partial structure corresponding to the LUMO is broadened as a result of intermolecular B?B interactions between adjacent [B₂N₄] units along the stacking direction. Due to bonding interactions with La d orbitals, this band is significantly lowered in energy and occupied with one electron in the band structure of La₃(B₂N₄). This singly occupied band exhibits no band crossings but creates a semimetal-like band structure situation.     

Preferential energy transfer from N2(A) to specific energy levels of Cu atoms

Emission spectra resulting from reaction of “clean” N₂(A³ Σ_u⁺) with copper atoms were studied using a flowing afterglow apparatus. The population distribution of the Cu states was calculated from the spectrum; it indicates that Cu atoms are excited by nearly resonant energy transfer processes. N₂(A,v') + Cu(²S_{$\text{1}\text{2}$}) → N₂(X, v) + Cu^* , and that the transfer is most efficient for N₂(A,v') → N₂(X,v) transitions with large Franck-Condon factors. The preferential energy transfer results in population inversion between some of the Cu states.     

Energy transfer processes in reactions of He(2 3S) and Ne(3P0,2) with CS2

A comparative spectroscopic study in the visible and ultraviolet ranges was conducted on the flowing afterglows resulting from the reactions of He(2 ³S) and Ne(³P_0,2) metastables with CS₂. Penning ionization was found to be the predominant energy transfer process. However, electron—ion recombination within the afterglows constitutes a major secondary process and gives rise to the most intense emitting system, CS(A ¹ Π → X ¹Σ⁺). Both afterglows were found to produce the CS⁺₂($\text{B}$²Σ⁺_u-$\text{X}$²Π_g), CS⁺₂($\text{A}$²Π_u-$\text{X}$²Π_g) and CS(a ³Π-X ¹Σ⁺) emission systems as well as some atomic sulfur emission lines. Some intensity differences were observed and are interpreted in terms of energetics and the formation mechanisms of the emitting species. A moderately strong CS⁺(A ²Π_i-X ²Σ⁺) emission system was also observed in the ehlium afterglow. In addition, a weak, sharp group of bands in the 390–420 nm range in the helium afterglow has been determined to be due to the presence of a small amount of He⁺ ions. This group of bands consists of two overlapping emission systems and are identified as CS(B ¹Σ⁺ → A ¹Π) and CS⁺(B ²Σ⁺ → A ²Π_i).     

Capture of aromatic carboxylate anion through second sphere coordination: Topological complementarity of [cis-Co(en)2(N3)2] and ions

[cis-Co(en)₂(N₃)₂]C₇H₃ClNO₄·1.25H₂O (Cocnb) was synthesised and detailed packing analyses were undertaken to delineate the topological complementarity of [cis-Co(en)₂(N₃)₂]⁺ and a 2-chloro-4-nitro benzoate anion (cnb) for second sphere coordination in the crystal lattice. The complex was completely characterised by elemental analyses, spectroscopic studies (IR, UV/visible, ¹H and ¹³C NMR). The compound crystallizes in the monoclinic (space group C2/c) with a = 21.9843(18), b = 8.7959(7), c = 23.0121(18) Å, β = 116.426(1)°, V = 3984.9(6) Å³, and Z = 8. In the crystal lattice, discrete ions of [cis-Co(en)₂(N₃)₂]⁺ and cnb are arranged in A–B–A–B pattern (in both a and c directions of the lattice) forming columns of anions and cations. The anionic columns are π stacked and are involved in extensive hydrogen bonding interaction. It appears that the topological feature of [cis-Co(en)₂(N₃)₂]⁺ is conducive for generating second sphere interactions with aromatic carboxylates. This strategy may be used as a viable method for the capture of aromatic carboxylate anions.     

Synthesis and reactivity of new heterodinuclear iron/rhenium Cx complexes of the formula (η-C5Me5)Re(NO)(PPh3)(CC)n(η-dppe)Fe(η-C5Me5) (n = 3, 4): Redox properties and a dicobalt hexacarbonyl adduct

We report in this communication the synthesis and characterization of two Fe/Re heterodinuclear complexes 3_n of formula (η⁵-C₅Me₅)Re(NO)(PPh₃)(CC)_n(η²-dppe)Fe(η⁵-C₅Me₅) (n = 3, 4) as well as the hexacarbonyl dicobalt adduct (4) of the hexatriynediyl complex 3₃. We show by cyclic voltammetry that the “electronic communication” between the organometallic endgroups and thereby the thermodynamic stability of the corresponding mixed-valent (MV) parent 3_n⁺ is strongly influenced by bridge extension or by complexation of the [Co₂(CO)₆] fragment. In the case of the hexatriynediyl complex, the MV complex 3₃⁺ or 4 can be isolated by performing the chemical oxidation of 3₃ at low temperature. Spectroscopic studies of this compound and of other stable oxidized redox congeners should now help us to unravel how bridge extension modifies the electronic communication between the different redox-active endgroups in this family of unsymmetrically-substituted polyynediyl compounds.     

Resonance Raman spectroscopy of mass selected Al2 in an argon matrix

In an excitation range of 620–760 nm, resonance Raman spectra of aluminum dimers (Al₂) in an argon matrix have been obtained for the first time. Temperature annealing experiments were performed to remove Raman lines attributed site effects caused by the Al₂/Ar matrix. We observe a single fundamental at 293.3 (5) cm⁻¹ along with a progression up to 1149 (1) cm⁻¹. Taking successive differences of band centers we obtain spectroscopic constants for the ground state fundamental, ω_e=297.5 (5) cm⁻¹, the anharmonicity, ω_ex_e=1.68 (8) cm⁻¹. Our results are in close agreement with previous experimental results for Al₂ which designate the ground state as a ³Π_u state, and may be considered as confirmation of this assignment.     

Synthesis, Structure, and Physical Studies of the New β-LiVOAsO4 Compound

Two new compounds of the A_xMOXO₄ family, β-LiVOAsO₄ and β-VOAsO₄, have been synthesized by solid state reaction and electrochemical lithium deintercalation from β-LiVOAsO₄, respectively. Both compounds are isostructural and are built like other β-VOXO₄ (X=S, P) by (VO₅)_∞ chains of distorted VO₆ octahedra connected via corner-shared AsO₄ tetrahedra. For β-LiVOAsO₄ the additional Li⁺ ions occupy chains of edge-shared octahedra running perpendicularly to the (VO₅)_∞ chains. The one-dimensional antiferromagnetic behavior suggested by the structure has been experimentaly confirmed. It is shown that lithium deintercalation occurs through a first-order transition at 4.02 V vs Li⁺/Li⁰. From chemical bond considerations it is shown why the redox potential of a given transition element M in a six-fold coordination involving (M=O)^m+ units lies between those observed in oxides and in M₂(XO₄)₃ compounds with (XO₄)ⁿ⁻ oxo anions (X=S, P, As).     

Spectroscopic Study of the Interaction of the Pd(acac)(C3-acac)PPh3Complex with BF3OEt2 in the Presence of PPh3

The interaction between the components of a catalytic system Pd(acac)(C³-acac)PPh₃+nPPh₃+ mBF₃OEt₂(where n= 1–4, m= 0.25–4, and acac is the acetylacetonate ligand) in benzene is examined by UV and IR spectroscopy. With a relative excess of PPh₃(n> m), acacH and [Pd(acac)(PPh₃)₂]⁺BF^– ₄were the main products, whereas BF₂acac and a polynuclear complex of PdF₂with PPh₃also containing Pd²⁺(BF^– ₄)₂units were formed with a relative excess of BF₃OEt₂(n< m).     

Electronic structure and reactivity of Mg+(H2O)n cluster ions

Electronically excited states of magnesium-water cluster ions, Mg⁺(H₂O) _n ,n=1–5, are studied by photodissociation after mass selection. The observed photodissociation spectra are assigned to the²P–²S type transitions localized on the Mg⁺ ion with the aid of ab initio CI calculations. In addition to evaporation of water molecules, photoinduced intracluster reaction to produce MgOH⁺(H₂O) _n is found to occur efficiently, with pronounced size dependence. The intriguing features observed in the mass spectrum of nascent cluster ions are discussed in relation to the stepwise solvation of this reaction.     

Fast calculation of excited-state potentials for rare-gas diatomic molecules: Ne2 and Ar2

A fast method for obtaining excited-state potentials of rare-gas diatomic molecules is described. Two types of excited orbitals are used: molecular orbitals calculated in the field of a singly charged molecular ion, and atomic orbitals (properly symmetrized) obtained in a similar atomic system. The RPA equations are solved within the manifold of excitations from the highest occupied orbital in each symmetry to the lowest excited orbital of either type in each symmetry. A simple model for estimating the dynamic correlation correction to excitation (and ionization) energies is given. Applications to excited states of Ne₂(^1,3Σ⁺_{g, u}, ^1,3Π_{g, u}) and Ar₂(^1,3Σ⁺_{g, u}) are described. Two-electron integral transformations involve only three orbitals of each symmetry, and the RPA matrices are four-dimensional. The computational effort required for all excited-state potentials adds less than one-tenths (in terms of computer time) to the effort involved in the preliminary ground state Hartree—Fock calculations. The resulting potentials compare favorably with more elaborate CI calculations and give good agreement with spectroscopic and scattering data. Potential curves for the molecular ions are also given.     

Ni + B2H6: Spectroscopic observations on NiB and NiH

An electronic spectrum of the nickel monoboride radical has been observed for the first time, in a reaction between a nickel plasma and diborane. Numerous bands of ⁵⁸Ni¹⁰B and ⁵⁸Ni¹¹B have been recorded between 442 and 503 nm in laser-induced fluorescence (LIF). Dispersed fluorescence experiments have also been performed. The LIF spectrum is dominated by a strong progression of bands of a [19.7]²Σ⁺–X²Σ⁺ transition. Analyses have been carried out to yield the following ⁵⁸Ni¹¹B ground state parameters: r₀ = 0.1698 nm, ω_e = 778 cm⁻¹, ω_ex_e = 4.9 cm⁻¹. Strong signals from NiH have also been observed.