A study of the UV—visible absorption spectrum of molecular chlorine

The UV—visible absorption spectrum of molecular chlorine at 298 K was investigated in the wavelength range 200–550 nm with a spectral resolution of 0.2 nm. Except for minor discrepancies, the absorption cross-sections are in agreement with those found in the literature. In the region 250λ-550 nm, the Cl₂ spectrum can be adequately described by a semi-empirical function of the wavelength A (in vacuum) and temperature T

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where TANH=tanh(hcx559.751 cm⁻¹/2kT). The absorption of solar radiation by the weak continuum around λ_max=406.5 nm contributes 9% or more of the photodissociation of molecular chlorine in the atmosphere, but the banded Cl₂ features (λ 479 nm) are of negligible atmospheric significance.     

Structures of the mono-acid cations of 4-aminoazobenzene and its derivatives

Conflicting views exist on the structures of the mono-acid cations of 4-aminoazobenzene and its derivatives. The azonium structure (I) and the ammonium structure (II) have been separately upheld as correct, but detailed examination of spectroscopic data shows that both forms exist in solution as tautomeric equilibrium mixtures (I

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II).     

Influence of solvents on the insertion of methacrolein into zirconacyclopropenes

The reaction of Cp₂Zr(L)(η²-Me₃SiC₂) (L = THF, py) with equimolar amounts of H₂C = CMe-CHO at room temperature depends strongly on the ligands L and the solvents that are used. With L = THF, in the THF solution the insertion product

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1 was isolated, whereas by conducting the reaction in n-hexane solution an alkyne substitution with 1,4-coordination of the methacrolein takes place and the binuclear complex [

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2 was obtained. In conttrast, with L = py (a stronger ligand) only a 1:1 ratio of 1 and 2 was observed in both THF and in n-hexane. At 50°C complex 1 was converted into 2 and the alkyne was eliminated quantitatively.

Complexes 1 and 2 were characterized by IR and NMR spectroscopical measurements and 1 by an additional X-ray structure determination.     

Formation d''etats triplets du biacetyle dans sa reaction en phase gazeuse avec un plasma froid d''azote

The behaviour of the biacetyl molecule (BA) in a cold plasma, obtained by extraction of reactive species from a nitrogen plasma generated in a microwave discharge, is discussed. When the partial pressures of nitrogen and biacetyl are approximately equal (p_N2 ≈ 0.60 Torr, p_BA ≈ 0.55 Torr), the emission of the ³A_u---¹A_g transition of biacetyl is observed with a vibrational structure. On reaction of biacetyl with nitrogen cold plasma preferentially enriched in N₂(A³Σ⁺_u), an enhancement of the emission intensity of the phosphorescence of biacetyl is observed. The initiator of this transition is the triplet state BA(³B_u) which originates from an isoenergetic transfer from N₂(A³Σ⁺_u) according to the overall mechanism

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Chelating diphos ligands with inorganic backbones. Crystal structure of [PtCl2{(PPh2O)2SiPh2}]

The metallo-phosphaalkenes (η⁵-C₅Me₅)(CO)₂FeP=C(R)(SiMe₃) (Ia: R = SiMe₃, Ib: R = Ph) and MeO₂C---CC---CO₂Me undergo a dipolar [3+2]-cycloaddition to afford the metallo-heterocycles [(η⁵-C₅Me₅)(CO)

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=C(R)SiMe₃] (IIIa,b) with exocyclic P=C double bonds.     

Chemistry of polyfunctional molecules-123. Reactions of BiBr3, SbI3 and AsI3 with LiN(PPh2)2; X-ray structure of a cyclophosphazene salt containing arsenic(I)

BiBr₃ or SbI₃ react at 20°C with LiN(PPh₂)₂ (1) to give elementary Bi or Sb and the P---P coupled phosphazene ligand Ph₂P---N=PPh₂---PPh₂=N---PPh₂ (2). The reaction of AsI₃ with 1 at room temperature formed yellow needles of the eight-membered heterocycle (3), whereas AsI₃ interacted at 80°C with 1 in the molar ratio of 1:3 to give elementary arsenic and 2. Treatment of AsI₃ and 1 at 20°C in a 1:2 stoichiometry yielded the seven-membered, cyclic arsenium(I) salt

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I·4THF (5·4THF), which was characterized by elemental analysis, conductivity, mass, IR and NMR spectroscopy and single-crystal X-ray structural analysis.     

Electronic spectra of organic molecules and their interpretation—IV Effect of terminal atoms with lone electron pairs on the K-bands of conjugated systems

The effect of the hydroxyl, methoxyl, mercapto, methylmercapto, and amino groups as well as of the charged O⁻ and S⁻ atoms (X) at the ends of the conjugated systems (1) and (2) on the position of the corresponding K-bands is discussed.

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The conclusions of earlier investigations are confirmed. The “effective” electron migration in one direction along the absorbing conjugated system (indicated by the long arrow) determines almost exclusively the stability of the observed excited state. The displacement of a K-band to longer wavelengths on introduction of a terminal group (X) can be due either to an electron shift in the substituted system coinciding with the direction of the effective electron migration of the transition or to an increased electron polarisability of the terminal group itself.

A consistent qualitative, but very detailed, theoretical interpretation of these observations is possible by a consideration of the electronic perturbations in the excited state due to Heisenberg resonance, if the molecules are accepted as being built up of localised bonds and involving inductive (inductomeric) electron shifts only.     

Kinetics of formation of intermediates in silver ion assisted aquations

There is kinetic evidence of the formation of [Co(NH₃)₅NCSAg₃]⁵⁺ in the interaction of [Co(NH₃]⁵NCS]²⁺ with Ag⁺ in aqueous solution, with pseudo-first-order formation rate constant k = 0.158 s⁻¹ for the forward reaction in the following equation at 25°C and [Ag⁺] in the range of 1.23–5.0 × 10⁻² mol dm⁻³ and 0.10 ionic strength (NaClO₄):

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Additionally, the formation constant, β₂, for [Co(NH₃)₅NCSAg₂]⁴⁺ has been determined to be log β₂ = 4.717. For the [Rh(NH₃)₅I]²⁺-Ag⁺ reaction there is evidence of an outer-sphere interaction with rate constants of k₂ = 670 dm³ mol⁻¹ s⁻¹ at 25°C and 0.10 ionic strength. This outer-sphere species undergoes further reaction to give the silver ion containing intermediates of the aquation reactions.     

Simple charge transfer complexes of some new and of some known heterocyclic compounds of selenium and tellurium

Charge transfer (CT) complexes (1:1) of 2,5-dihydrotellurophene and the 3-methyl and 3,4-dimethyl compounds with TCNQ and tetrachlorobenzoquinone (TCB) are reported. The organotellurium compounds failed to give complexes with p-dinitrobenzene (DNB). The variation of solid state (disc) conductivity with temperature and as a function of methyl substituents is considered. The complexes show semi-conducting behaviour and a consideration of these data, together with IR and UV spectroscopic data, in comparison with those for 1,3-dihydro-2-telluraindene given the following order of donor power with respect to TCNQ:

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With respect to a given donor, the order to acceptor power is TCNQ> TCB> DNB.

1,3-Dihydro-2-selanaindene forms a complex with TCNQ. The molecular ionisation potential of the selanaindene is 7.4 eV (by mass spectroscopy) and it has been shown that the compound may be electrochemically oxidized to materials such as C₈H₈SePF₆.

New quinoxalino-1-chalcogenacyclopentanes are reported; namely those derived from selenium, and for the 7,8-dimethyl series, those based on both selenium and tellurium. Their preparation and characterisation are described, and their chemistry shown to be strongly analogous to that of quinoxalino-1-telluracyclopentane. CT complexes of the new Se^II and Te^II compounds (1:1) are prepared with TCNQ which are believed to be strongly ionic.     

Ligand migrations during the formation of some palladium-rhodium heterodinuclear complexes

A new Pd(I)-Rh(II) heterodinuclear complex, trans-(NC)₂---(CH₃0)₃PRh(μ-dppm)₂PdC1 (2a), was prepared by treatment of [(cod)RhCI]₂ with (CH₃0)₃P and trans-(NC)₂Pd(dppm)₂ (1) (dppm = bis(diphenylphosphino)methane, COD = 1,5-cyclooctadiene) and characterized by ³¹P NMR spectroscopy and single-crystal X-ray structure determination. The single crystal of complex 2a is triclinic; its space group

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, = 94.43(3), β = 106.55(3), γ = 87.86(3)°. The Rh---Pd bond distance is 2.7835(5) Å. The molecular structure of this complex suggests that its formation reaction includes: (i) ligand migrations of the Cl⁻ from the Rh center to the Pd center and the two CN⁻ groups from the Pd center to Rh center; (ii) the intermetallic one-electron transfer indicated by the alteration from Rh(I) and Pd(II) to Rh(1I) and Pd(I) respectively; (iii) the Pd(I)---Rh(II) bond formation by pairing one electron from Rh(II) with one electron from Pd(I). The differences of chemical shifts of the phosphorus atoms coordinated to the Pd center in the Pd---Ag complexes and the Pd---Rh complexes are discussed.     

X-ray Peltier cooled detectors for X-ray fluorescence analysis

The recent results on development of X-ray Si(Li), Si-planar and CdTe p-i-n detectors cooled by Peltier coolers for fabrication of laboratory and portable XRF analysers for different applications are discussed.

Low detection limits of XRF analysers are provided by increasing of detectors sensitive surface; improvement of their spectrometrical characteristics; decreasing of front-end-electronics noise level; Peltier coolers and vacuum chambers cooling modes optimization.

Solution of all mentioned tasks allowed to develop Peltier cooled detectors with the following performances:

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Advantages and disadvantages of all types of detectors for X-ray fluorescence analysis are compared. Spectra are presented. Application of different XRF analysers based on developed detectors in medicine, environmental science, industry, cryminalistics and history of art are demonstrated.     

Dipole polarizability pseudospectra and C6 dispersion coefficients for H2–H2

Pseudostate decomposition of static dipole polarizabilities for ground state H₂⁺ from a Givens-Householder diagonalization of the excitation operator (

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H" height="17" width="20">₀−E₀) over an N-term basis of appropriate symmetry allows for a rapidly convergent evaluation of C₆ dispersion coefficients for H₂⁺–H₂⁺. 27-term pseudospectra of hypergeneralized James functions with a 30-term GGJ⁺ unperturbed wavefunction with an optimized scale factor δ=0.918 at R=2₀ give C₆ and γ₆ values that are accurate to no less than nine significant figures.     

Isolation of a diketone species that is allylically bound to tungsten, and its relationship to a tungsten η-ketone complex

The diketone complex [W(CO)₂(η-C₅H₄Me){η³-

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(H)---C(O)---C₅Me₅}] (3) was isolated from the reaction of PhC₂H with a mixture of [Ni(CO)I(η-C₅Me₅)] and [W(CO)₃(η-C₅H₄Me)]⁻. Complex 3 contains an organic diketone fragment that is bound in a π-allyl fashion to a tungsten atom. It was fully characterized by standard spectroscopic techniques and by a single-crystal X-ray diffraction study. The relationship of complex 3 to a structurally characterized cyclopentadienyl tungsten η²-ketone species 1, and the likelihood that 3 and the methylcyclopentadienyl analog of 1 share common intermediates, are discussed.     

Liquid-phase Oppenauer oxidation of primary allylic and benzylic alcohols to corresponding aldehydes by solid zirconia catalysts

Hydrous zirconia and grafted zirconium 1-propoxide catalysts were found active in the Oppenauer oxidation of cinnamyl alcohol, geraniol and 4-tert-butylcyclohexanol (cis- and trans-). The most active hydrous zirconia catalysts were formed by calcining at 250–300 °C. Grafted zirconium 1-propoxide on silica gel and MCM-41 were active in the Oppenauer oxidation of geraniol with high selectivity to the desired citral product. However, over an acidic support such as AlMCM, the grafted zirconium 1-propoxide catalysed the dehydration and isomerisation of the alcohol, leading to low yield to citral. Also, furfural was found to be an efficient oxidant for the titled Oppenauer oxidation. Other solid catalysts such as γ-Al₂O₃, Na–Al₂O₃, zeolite beta and Mg/Al hydrotalcite showed only moderate catalytic activity and selectivity in the Oppenauer oxidation of geraniol. As compared to other solid catalysts, hydrous zirconia solid catalysts used in this work are active and selective towards the formation of desired carbonyl oxidation products; additionally, these solid zirconia catalysts are easy to prepare and recycle, and applicable to different alcohol substrates.

Graphical abstract

Hydrous zirconia calcined at 250–300 °C and grafted zirconium 1-propoxide solid catalysts were found to be efficient for the Oppenauer oxidation of cinnamyl alcohol, geraniol and 4-tert-butylcyclohexanol in toluene when furfural was used as the oxidant.

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Nuclear magnetic resonance studies for the chiral recognition of the novel chiral stationary phase derived from 18-crown-6 tetracarboxylic acid

Enantioselectivities observed in high-performance liquid chromatography (HPLC) with the novel chiral stationary phase (CSP-18C6I) derived from (+)-18-crown-6 tetracarboxylic acid (18C6H₄) were investigated by using nuclear magnetic resonance (NMR) spectrometry. The elution orders in CSP-18C6I, that is, the S-enantiomer of 1-(1-naphthyl)ethylamine (1-NEA) and the

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-enantiomer (S-form) of alanine-β-naphthylamide (Ala-β-NA) eluted prior to each corresponding enantiomer, were successfully explained on the basis of the apparent binding constants (K_a) of the enantiomers to the CSP moiety which were calculated from ¹H-NMR experiments. Detailed HPLC and NMR studies for the chiral recognition of racemic amino compounds with 18C6H₄ hosts showed that ¹H-NMR spectrometry is a useful technique for the investigation of the chiral recognition mechanism in HPLC. Additionally, it was found 18C6H₄ can be recommended as a useful chiral shift reagent for the enantiomeric excess determination by ¹H-NMR.     

Synthesis and characterisation of four- and eight-membered ring auralactam complexes

The reactions of the cyclo-aurated gold(III) dihalide complex [{C₆H₃(CH₂NMe₂)-2-(OMe)-5}AuCl₂] with N-cyanoacetylurethane [NCCH₂C(O)NHCO₂Et], 2-benzoylacetanilide [PhC(O)CH₂C(O)NHPh] and acetoacetanilide [MeC(O)CH₂C(O)NHPh], and [{C₆H₄(CH₂NMe₂)-2}AuCl₂] with acetoacetanilide in dichloromethane with excess silver(I) oxide gives the first examples of auralactam complexes, containing (O)---CHR′ four-membered rings. A single-crystal X-ray diffraction study on the complex [{C₆H₄(CH₂NMe₂)-2}A H(COMe)}] reveals similar structural features to related metallalactam complexes of platinum(II) and palladium(II). When a CDCl₃ solution of the complex [{C₆H₃(CH₂NMe₂)-2-(OMe)-5}A HCN}] is allowed to stand for 18 h, a novel dimerisation reaction occurs, giving the insoluble product [{C₆H₃(CH₂NMe₂)-2-(OMe)-5}Au{N(CO₂Et)C(O)CHCN}]₂·2CDCl₃, characterised by an X-ray structure determination. The dimer contains an eight-membered A

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ring.     

Enantioselective organic syntheses using chiral transition metal complexes V. (2S,3S)-Bis(dibenzophospholyl)butane, a rigid (S,S)-CHIRAPHOS analog

The P–Ph cleavage of phenyldibenzophosphole (1) with lithium in THF gives lithium dibenzophospholide (2). Reaction of 2 with ethyleneglycol ditosylate produces the known chelate ligand 1,2-bis(dibenzophospholyl)ethane (3) in good yield. Similarly, 2 and (2R,3R)-butanediol ditosylate give the new chiral chelate ligand (2S,3S)-bis(dibenzophospholyl)butane (4). Ligand exchange of [CpRu(PPh₃)₂Cl] with 3 or 4 yields the halfsandwich complexes [CpRu(C₁₂H₈PC₂H₄PC₁₂H₈)Cl] (5) and [CpRu((S,S)-C₁₂H₈PCHMeCHMePC₁₂H₈)Cl] (6). Complex 6 was characterized crystallographically (monoclinic, space group P2₁ (no. 4), a=820.6(4), b=1501.0(3), c=1172.8(6) pm, β=108.87(2)°, V=1.367(1)×10⁹ pm³, Z=2). The most conspicuous feature of the structure of 6 is the perfect coplanarity of the two dibenzophosphole moieties imposed by their steric interaction with the Cp ligand. Complex 6 and the thiophene complex [CpRu((S,S)-C₁₂H₈PCHMeCHMePC₁₂H₈)(SC₄H₄)]BF₄ (7) derived therefrom are remarkably unreactive with regard to ligand substitutions. A possible explanation is the lack of intramolecular

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–C stabilization en route to the transition state of ligand substitution. The enantiomeric purity of 6 and 7 could nevertheless be demonstrated by conversion to diastereomerically pure [CpRu((S,S)-C₁₂H₈PCHMeCHMePC₁₂H₈)((S)-CNCHMePh)]BF₄ (8).     

A new spline approach for data fitting

This paper presents an extension of the Modified Spline Technique (MST) formulation for data fitting named power spline, which gives consistent results for sets of data of concave and convex curves. This method is based on a technique which couples an implicit formulation of the maximum likelihood principle to the spline method, making the method suitable to fit data when no physical model is available. The MST method proved to be better than to the spline method and the extended spline fit technique (EST), because it provided accurate results for the first and second derivatives in sets of data where the EST solution developed inaccuracies. The EST method is a formulation that couples Least Squares to the spline method. There are, however, some sets of data where the MST method would show inconsistent solutions for the first and second derivatives. The power spline method eliminates these problems for concave or convex curves. Another improvement on the method is a more flexible choice for the interval boundaries.¹     

New regularities and an equation of state for liquids

Three regularities have been introduced for liquids (T < T_C and ρ > ρ_C) based on average potential energy. The experimental data have been used to show the validity of the regularities. First, there exists near-linearity relation between and ρ for all isotherms of a liquid, where P_i and ρ are internal pressure and density, respectively. Second, changes linearly with ρ for each isotherm of any liquid, where Z and V_m are compressibility factor and molar volume, respectively. Third, a new regularity using the definition of bulk modulus and our new equation of state between reduced bulk modulus and density has been introduced, that is versus ρ must be linear for all isotherms of a liquid where B_r is the reduced bulk modulus.

A new equation of state has been also derived. The density of some liquids in the extensive ranges of temperature and pressure has been calculated using the new equation of state. The densities calculated from this equation agree with experiment to better than 0.3%. The new equation of state can predict internal pressure, thermal expansion coefficient, and isothermal compressibility of liquids within experimental error.     

Non-isothermal thermoanalytical studies on the salt roasting of chalcopyrite using KCl

In an earlier study [1], the isothermal kinetics of salt roasting of chalcopyrite under an oxidizing atmosphere using KCl was studied in the temperature range 523–773 K. The salt roasting reaction was found to be chemically controlled at temperatures below 600 K both under static air and oxygen atmosphere. At higher temperatures, the process was not thermally activated because of a change in the chemistry of the process. In the present study, the salt roasting of chalcopyrite using KCl under oxygen and static air atmosphere was studied by non-isothermal thermoanalytical studies up to 723 K. The effect of salt content, heating rate and particle size on the salt roasting behavior was studied using TG/DTA techniques at a programmed linear heating rate. The TG and DTA studies reveal two distinct chemical processes, one operative up to 620 K and the other from 620 to 723 K. The integral method of Coats and Redfern was used for the treatment of non-isothermal kinetic data. The non-isothermal analysis confirmed the chemical control mechanism at temperatures below 620 K. However, the activation energy for the process derived from non-isothermal thermogravimetric analysis is almost twice as that deduced from isothermal measurements. In the temperature range 620–723 K, the kinetic data still obeys the interfacial reaction control model although the activation energy in this temperature range is very low.