Some Mo¨ssbauer and X-ray investigations of theα2-Snformation during the reduction of SnCl2 water solutions

Tin structures with very high values of the isomer shifts (δ = +4.3 ± 0.1 mm/sec and δ = +7 ± 0.4 mm/sec) of the Mo¨ssbauer lines, have been observed not only in thin tin films but also in bulk samples. The samples have been obtained by the reduction of SnCl₂ water solutions with Mg, carried out either in the presence of ferromagnetic impurities (Fe, Co, Ni) or in an external magnetic field. The parallel X-ray studies are in accordance with the RHEED observations of thin tin films. The temperature dependence of the Mo¨ssbauer effect on samples rich inα₂-Snhas been studied and microcalorimetric measurements on samples containingβ₁-Snandα₂-Snhave also been performed.     

Proton magnetic resonance spectra of 2,6-disubstituted naphthalenes

The spectra of several 2-methyl-6-R-disubstituted naphthalenes (R=H, Me, I, NO₂, Cl, SO₂Cl, OH, OMe, COMe, Br, F and NHCOMe), have been analysed. Chemical shift and coupling constant values of these compounds are presented. The proton chemical shifts have been found to correlate with the ortho parameter, Q.     

Direct Syntheses of Bis(tetraphenylphosphonium) and Bis(ethyltriphenylphosphonium) Hexabromo‐diselenates(II), [PPh4]2[Se2Br6] and [PEtPh3]2[Se2Br6]. The Crystal Structure of [PEtPh3]2[Se2Br6]

Brown crystals of [PPh₄]₂[Se₂Br₆] ( 1 ) and [PEtPh₃]₂[Se₂Br₆] ( 2 ) were obtained when selenium and bromine reacted in acetonitrile solution in the presence of tetraphenylphosphonium bromide and ethyltriphenylphosphonium bromide, respectively. The crystal structure of 2 has been determined by X‐ray methods and refined to R = 0.0420 for 4161 reflections. The crystals are monoclinic, space group P2₁/n with Z = 2 and a = 13.055(3) Å, b = 12.628(3) Å, c = 13.530(3) Å, β = 92.40(3)° (293(2) K). In the solid state structure of 2 the dinuclear hexabromo‐diselenate(II) anion is centrosymmetric and consists of two distorted almost square‐planar SeBr₄ units sharing a common edge through two bridging Br atoms. The terminal Se^II–Br bond distances are found to be 2.419(1) and 2.445(1) Å, the bridging μBr–Se^II bond distances 2.901(1) and 2.802(1) Å.     

Trans influence and charge transfer transitions X → Co in cobalt (III) complexes of the type trans [CO(en)2XY]z

The energies of the CT transitiopns X → Co have been measured for a series of compounds of the type trans [CO(en)₂XY]^+z, with X = Cl, Br and Y = Cl, Br, NH₃, OH, NCS, No₂, SO₃, CN. They depend upon the nature of the Yl igand. Values of the optical electronegativity of the CO d_z2 orbitals have been calculated, showing that the covalent character of the CoX bond increases in the following order of the Y ligands: NCS ≈ NH₃ ≈CN < OH < NO₂ < Cl ≈ Br < SO₃. This result is discussed along with the variations of the Co bonding forces.     

Benchmark compounds. Structures of cobalt(II) complexes of triphenylphosphine- and triphenylarsine oxides

The structures of the Co(OPPh₃)₂Cl₂, Co(OPPh₃)₂Br₂, Co(OPPh₃)₂I₂, Co(OAsPh₃)₂Br₂ and Co(OAsPh₃)₂(NO₃)₂ complexes have been determined by X-ray diffraction methods; all have pseudo-tetrahedral co-ordination for cobalt.     

Large 1,3,5-triazine-based ligands coordinating transition metal ions: syntheses and structures of the ligands and the ball shaped nanometer-scaled Co complex [Co(2,4-R-6-R′-1,3,5-triazine)2](Br1.7(OH)0.3) · 4.8H2O {R = bis(2-diphenylmethylene) hydrazinyl; R′ = piperidin-1-yl}

Two new, large 1,3,5-triazine-based ligands with only N-donor functions were synthesized as well as the Co(II) salt [Co(DHPTBenz)₂](Br_1.7(OH)_0.3) · 4.8H₂O (DHPTBenz = 2,4-bis-(2-diphenylmethylene)-hydrazinyl-6-piperidin-1-yl-1,3,5-triazine). Single crystal X-ray structures of the Co(II) complex, DHPTBenz, and 2,4-dichloro-6-(piperidin-1-yl)-1,3,5-triazine (DCPT) have been determined. The last compound was used as starting material for the tridentate DHPTBenz ligand. Spectroscopic data of the ligand and the starting materials are reported. The Co(II) ion in the complex is distorted octahedrally coordinated by six N atoms of two DHPTBenz ligands. One N atom of the triazine ring of each ligand bonds axially with short distances of 1.953(3) Å and 1.954(3) Å, respectively, whereas two of the hydrazine-N atoms of two ligands form the equatorial plane with an average Co–N bond distance of 2.313 Å. The complex cation has a slightly elongated, nanometer-scaled ball shape with the longest diameter of 1.82 nm.     

Thermal investigation of diamine complexes of Zn(II) in the solid state

The complexes [Zn(en)₃]X2·n H₂O, where en = ethylenediamine, X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄, n = 1 or 0.5, and [Zn(tn)₂]X₂·n H₂O, where tn=1,3-diaminopropane, X=Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄, n = 0 or 0.25, have been synthesized and their thermal investigations carried out. The complexes were characterized by elemental analysis and IR spectral data. These complexes have been observed to decompose through several isolable as well as non-isolable complex species as intermediates during heating. [Zn(tn)₂]SO₄ undergoes solid-state phase transition in the temperature range 126–145°C. ZnenSO₄ and ZntnX₂ (X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄) have been synthesized pyrolytically in the solid state from their corresponding mother diamine complexes. ZnenSO₄ and ZntnX₂ (X = Cl^?, Br^? or $\text{1}\text{2}$SO^2?₄) complexes decompose through non-isolable hemidiamine species. ZnX₂ (X = Cl^? or Br^?) complexes of tn undergo melting after formation of the monodiamine species. In contrast, the corresponding en complexes undergo melting at non-stoichiometric composition. Diamine (en or tn) is found to be bridging in all monodiamine (en or tn) complexes; whilst their mother complexes possess chelated en or tn. The thermal stability sequence of en and tn complexes of Zn(II) is ZnCl₂ < ZnBr₂ < ZnSO₄. ΔH values are reported for some steps of decomposition. Possible mechanistic paths have been reported for each step of decomposition.     

Ca2CoNbO6: A new monoclinically distorted double perovskite

The new Ca₂CoNbO₆ double perovskites has been synthesized by solid-state reaction and its crystal structure has been refined using X-ray powder diffraction data. Rietveld fit to the diffraction data shows that the compound is monoclinically distorted and adopts space group P21/n. The cell parameters are: a = 5.4797(1) Å, b = 5.6051(1) Å, c = 7.8119(2) Å, β = 89.96(1)°. The Co and Nb are found to be distributed over the six coordinated octahedral sites in rock salt arrangement. However, nearly identical ionic radii of Co and Nb lead to severe degree of anti-site disorder (31%). The refined Co–O and Nb–O bond lengths are 1.9788(2) Å and 2.0642(2) Å respectively.     

Copolymerization of vinyl chloride with sulphur dioxide—I molecular association between vinyl chloride and sulphur dioxide

The formation of VC-SO₂ and VC-(SO₂)₂ complexes in liquid mixtures of vinyl chloride (VC) and sulphur dioxide has been shown by (a) the freezing point composition diagram and (b) chemical shifts in the PMR spectrum of VC over the complete composition range. It is postulated that SO₂ can associate with the CC bond and the Cl atom. These complexes may be involved in the copolymerization and influence the composition and stereochemistry of the product. PMR spectra of VC-SO₂-ethane(E) mixtures with [SO₂] ? [E] ? [VC] gave K_v = 2·0 ± 0·5, 1·5 ± 0·1 and 1·1 ± 0·3 at 232·6, 272·6 and 301·3 K with ΔH_f⁰H_f = ?6·6 ± 1·4 kJ mol^?1 for the VC -(SO₂)₂ complex. The chemical shift of the trans β-proton was twice that of the other two protons. indicating that SO₂ adopts an asymmetric orientation to the double bond.     

Crystal and Molecular Structures of Three Salts of Λ-β 1-[Co(R,R-Picchxn)(R-Phe)]2+ (Picchxn=N,N 1-DI(2-Picolyl)-1,2-Diaminocyclohexane; Phe = Phenylalaninato(1−))

Single-crystal X-ray structures of Λ-β ₁-[Co(R,R-picchxn)(R-phe)]Br₂, Λ-β ₁-[Co(R,R-picchxn)(R-phe)]Br₂·3H₂O and Λ-β ₁-[Co(R,R-picchxn)(R-phe)]I₂ are reported. In each structure there are three formula units in the asymmetric unit. Considerable disorder attends the anions and water molecules of crystallisation. In every case the conformer adopted by the coordinated aminoacidate is such that the phenylalaninato side chain is extended in order to minimize non-bonded steric interactions with the Co(tetradentate)fragment. Such an arrangement is in accord with the fact that this kind of diastereoisomer does not participate in any strong intramolecular π-π or NH-π interaction.     

Contribution de la spectrometrie X à l'étude du manganèse dans les oxydes mixtes de structure spinelle: Analyse du spectre MnKβ et du seuil d'absorption K

Chemical shifts of Kβ_1,3 and Kβ₅ emission bands and X-ray absorption spectra near the K edge have been measured in several manganese spinel oxides with the metal in the formal oxidation states +2, +3, and +4. The position of line MnKβ_1,3 is determined mainly by the valence of manganese. The relative intensity of Kβ′ satellite with respect to the Kβ_1,3 line gives qualitative information about the presence of Mn(II) in mixed oxides. Mn(IV) oxides are characterized by a small chemical shift of the Kβ₅ band unlike Mn(II) and Mn(III) compounds. The first high resolution XANES spectra for these materials were performed at the DCI storage ring at LURE (Orsay, France). The chemical shifts ΔE (K absorption discontinuty) and ΔE_max (main peak) are correlated with the oxidation state of metal. Spectra of Mn³⁺ and Mn⁴⁺ ions in the octahedral environment are characterized by the splitting of 1s → 3d transitions (2 eV). In mixed oxides, the first Mn(II) 1s → 4s-4p transition is observed as a peak (or shoulder) located at 7 eV above the 1s → 3d transition. The study of the X-ray absorption fine structure in the near edge region can be used for qualitative solid-state analysis of mixed oxides such as NiMn₂O₄ or CuMn₂O₄.     

Structural characterization, magnetic behavior and high-resolution EELS study of new perovskites Sr2Ru2−xCoxO6−δ (0.5?x?1.5)

New oxides of general formula Sr₂Ru_2−xCo_xO_6−δ (0.5?x?1.5) have been synthesized as polycrystalline materials and characterized structurally by X-ray diffraction. For 0.5?x<0.67 the orthorhombic, Pnma, perovskite structure of the end member, SrRuO₃, is found. At x=0.67 a phase separation into an Ru-rich Pnma phase and a Co-rich I2/c phase occurs. The I2/c form is also found for x=1.0 but another orthorhombic phase, Imma, obtains for x=1.33 and 1.5. Reductive weight losses indicate negligible oxygen non-stoichiometry, i.e., δ∼0, for all compositions even those rich in Co. High-resolution electron energy loss spectroscopy (EELS) indicates that cobalt is high-spin Co³⁺ or high-spin Co⁴⁺ for all x. Appropriate combinations of Ru⁴⁺, Ru⁵⁺, HS Co³⁺ and HS Co⁴⁺ are proposed for each x which are consistent with the observed Ru(Co)-O distances. Significant amounts of Co⁴⁺ must be present for large x values to explain the short observed distances. Broad maxima in the d.c. susceptibilities are found between 78 and 97 K with increasing x, along with zero-field-cooled (ZFC) and field-cooled (FC) divergences suggesting glassy magnetic freezing. A feature near 155 K for all samples indicates a residual amount of ferromagnetic SrRuO₃ not detected by X-ray diffraction.     

Four‐bond deuterium isotope effects on the chemical shifts of amide nitrogens in proteins

An approach towards precision NMR measurements of four‐bond deuterium isotope effects on the chemical shifts of backbone amide nitrogen nuclei in proteins is described. Three types of four‐bond ¹⁵ N deuterium isotope effects are distinguished depending on the site of proton‐to‐deuterium substitution: ⁴ΔN(N_i‐1D), ⁴ΔN(N_i+1D) and ⁴ΔN(C_β,i‐1D). All the three types of isotope shifts are quantified in the (partially) deuterated protein ubiquitin. The ⁴ΔN(N_i+1D) and ⁴ΔN(C_β,i‐1D) effects are by far the largest in magnitude and vary between 16 and 75 ppb and ?18 and 46 ppb, respectively. A semi‐quantitative correlation between experimental ⁴ΔN(N_i+1D) and ⁴ΔN(C_β,i‐1D) values and the distances between nitrogen nuclei and the sites of ¹H‐to‐D substitution is noted. The largest isotope shifts in both cases correspond to the shortest inter‐nuclear distances. Copyright © 2013 John Wiley & Sons, Ltd.     

Standard enthalpy of formation of fullerene bromide C60Br24

The enthalpy of the combustion of C₆₀Br₂₄ · 2Br₂ has been measured using a rotating-bomb calorimeter as follows: Δ _c H ⁰(C₆₀Br₂₄ · 2Br₂, cr) = (?25986 ± 166) kJ/mol. The result has been used to calculate the standard enthalpy of formation, ΔfH ⁰(C₆₀Br₂₄ · 2Br₂, cr) = (2375 ± 166) kJ/mol. The enthalpies of formation of C₆₀Br₂₄ (cr) and dissociation of the C-Br bond have been estimated. The latter value has been compared with enthalpies for the C-X (X = H, F, Cl, Br) bonds in fullerene derivatives and organic compounds.     

Synthèse et analyse radiocristallographique de la solution solide K2PdCl4–xBrx (0 < x < 4)

Preparation and crystal structure determination (by X-ray single crystal measurements) of the K₂PdCl_2.81Br_1.19, K₂PdCl_2.64Br_1.36, K₂PdCl_2.41Br_1.59, K₂PdCl_1.73Br_2.27, and K₂PdCl_0.99Br_3.01 compounds are reported. All these compounds crystallise in the same centrosymmetric space group P4/mmm. The tetragonal cell (a ≈ 7.3 Å; c ≈ 4.2 Å) contains one Pd atom, which lies on the C4 axis. The square-planar 〚PdX₄〛^2– ions (X = Cl, Br) are disordered. The Pd–X distances (2.348(2), 2.356(2), 2.362(2), 2.383(1), and 2.422(2) Å) have intermediate values between those previously observed for Pd–Cl (2.313 Å) in the K₂PdCl₄ compound and Pd–Br (2.444 Å) in the K₂PdBr₄ compound.     

Intrinsic Dynamic and Static Nature of Halogen Bonding in Neutral Polybromine Clusters,with the Structural Feature Elucidated by QTAIM Dual-Functional Analysis and MO Calculations

The intrinsic dynamic and static nature of noncovalent Br-∗-Br interactions in neutral polybromine clusters is elucidated for Br₄–Br₁₂, applying QTAIM dual-functional analysis (QTAIM-DFA). The asterisk (∗) emphasizes the existence of the bond critical point (BCP) on the interaction in question. Data from the fully optimized structures correspond to the static nature of the interactions. The intrinsic dynamic nature originates from those of the perturbed structures generated using the coordinates derived from the compliance constants for the interactions and the fully optimized structures. The noncovalent Br-∗-Br interactions in the L-shaped clusters of the C_s symmetry are predicted to have the typical hydrogen bond nature without covalency, although the first ones in the sequences have the vdW nature. The L-shaped clusters are stabilized by the n(Br)→σ*(Br–Br) interactions. The compliance constants for the corresponding noncovalent interactions are strongly correlated to the E(2) values based on NBO. Indeed, the MO energies seem not to contribute to stabilizing Br₄ (C_2h) and Br₄ (D_2d), but the core potentials stabilize them, relative to the case of 2Br₂; this is possibly due to the reduced nuclear–electron distances, on average, for the dimers.     

Structure of Aqueous Gallium(III) Bromide Solutions Over a Temperature Range 80–333 K by Raman Spectroscopy, X-ray Absorption Fine Structure, and X-ray Diffraction

The structure and complex formation of concentrated aqueous gallium(III) bromide (GaBr₃) solutions have been investigated over a temperature range 80–333 K by Raman spectroscopy, X-ray absorption fine structure (XAFS), and X-ray diffraction. The Raman spectra obtained at various [Br^?]/[Ga³⁺] molar ratios and temperatures have shown that complex formation between Ga³⁺ and Br^? occurs as a predominant species, with [GaBr₄]^? at [Ga³⁺] as high as 1～2 M (M = mol?dm ^?3) and [Br^?]/[Ga³⁺] ratios > ～2, and that cooling of the solutions favors the formation of the aqua Ga³⁺. The intermediate species were not seen in the Raman spectra. The XAFS data have revealed that the aqua complex has a sixfold coordination as [Ga(H₂O)₆]³⁺ with a Ga³⁺–H₂O distance of (1.96 ± 0.02) Å, whereas the [GaBr₄]^? complex has a Ga³⁺–Br^? distance of (2.33± 0.02) Å, and that vitrification of the aqueous GaBr₃ solution at liquid nitrogen temperature shifts the equilibrium toward the aqua complex. The X-ray diffraction data at different subzero temperatures have shown a tendency of decreasing Ga³⁺–Br^? and increasing Ga³⁺–H₂O interactions with lowering temperature, confirming the preference of aqua Ga³⁺ in the supercooled liquid state as well as in the glassy state. The Ga³⁺–H₂O distance of ～1.8 Å for the tetrahedral coordination was found in a 2.01 M gallium(III) bromide solution with a [Br^?]/[Ga³⁺] ratio of 3.7 and gradually increased to a value of 1.92 Å for octahedral geometry with decreasing temperature, suggesting that equilibrium shifts from [GaBr₄]^? to [Ga(H₂O)₆]³⁺ through intermediate species, [GaBr _n ]^(3?n)+ (n = 2 and 3). The Ga³⁺–Br^? and Br^?–Br^? distances within [GaBr₄]^? with an almost tetrahedral symmetry are (2.35± 0.02) and (3.82± 0.03) Å, respectively. The Ga³⁺ has the second hydration shell at (4.03± 0.03) Å and the hydration of Br^? is characterized with a Br^?–H₂O distance of (3.35± 0.02) Å at all temperatures investigated.     

Structural characterization of the Ta-rich part of the Ta-Al system

The Ta-rich part of the Ta-Al system has been investigated. On the one hand, the accommodation of the non-stoichiometry in the σ phase has been studied by Rietveld refinement of X-ray powder data obtained from different samples on both sides of the ideal composition (Ta₂Al, P4₂/mnm, tP30). On the other hand, the structure of the β phase has been determined ab initio from powder synchrotron data (analyzed composition Ta_50.7Al_49.3, refined composition Ta_52.6(5)Al_47.4(5) (Ta_45.2(4)Al_40.8(4)), stoichiometric composition Ta₄₈Al₃₈, mP86, P2₁/c, a=9.8707(1) Å, b=9.8766(1) Å, c=16.3539(2), β=116.478(1), R_B=2.6%). This phase is shown to be closely related to the group of the topologically close packed phases. In addition, phase relations have been accurately determined in the Ta-rich end of the system.     

ECE mechanism as a tool for the investigation of unstable metal complexes: Part I. Electrochemical reduction of trans-[CoBr2(N)4]+-type complexes on the mercury electrode

A polarographic investigation of trans-[CoBr₂(N)₄]⁺-type complexe where (N)₄ represents (NH₃)₄, (ethylenediamine)₂ and (propylenediamine)₂, has been carried out in acetate buffer solutions. These complexes gave two polarographic waves; the first wave corresponds to the reduction of Co(III) to Co(II) and the second to the reduction of Co(II) to Co(0). The relation between current and time of the first wave in a positive potential is dependent on the dissolution wave due to bromide ions produced by acid hydrolysis and parallel ECE mechanism. Overall reaction is as follows: at the electrode surface, [Co(III)Br₂(N)₄]⁺+e^-→[Co(II)Br₂(N)₄] [Co(II)Br₂(N)₄]+6H₂O→[Co(II)(H₂O₆]²⁺+2Br^-+(N)₄ 2Br^-+2Hg→Hg₂Br₂+2e and in the solution, [Co(III)Br₂(N)₄]⁺+2H₂O→[Co(III)(H₂O₂(N)₄]³⁺+2Br^-The effects of the acid hydrolysis of a tervalent cobalt complex on the current—potential curve were simulated.     

Ab Initio (GIAO) Calculations of Absolute Nuclear Shieldings for Representative Compounds Containing 1(2)H, 6(7)Li, 11B, 13C, 14(15)N, 17O, 19F, 29Si, 31P, 33S,and 35Cl Nuclei

Two kinds of ab initio calculations (B3LYP and HF) using the GIAO approach have been carried out for fifteen H, three Li, three B, eleven C, seven N, nine O, four F, three Si, four P, six S and five Cl containing derivatives. The calculated absolute nuclear shieldings have been compared with experimental absolute values (either measured or estimated from relative chemical shifts) when available or with relative chemical shifts (¹¹B, ³⁵Cl). The correlations range from good to excellent and only three compounds (PN, P₂H₂, SO₂) deviate significantly.