Synthesis,X-ray crystallography characterization,vibrational spectroscopy,and DFT theoretical studies of a new organic–inorganic hybrid material

A new hybrid material based on polyoxomolybdate, [C₂H₆N₂O–H]₃[(PO₄)Mo₁₂O₃₆] · 3H₂O (1), has been synthesized and characterized by elemental analysis, infrared and mass spectroscopy, proton nuclear magnetic resonance and single-crystal X-ray diffraction. Compound 1 crystallizes in the hexagonal system, space group R-3, a = 19.0833(6) Å, c = 20.8672(13) Å, V = 581.1(5) ų, Z = 6, R1 = 0.0202, wR2 = 0.0508. The methyluronium moiety and 12-molybdophosphate anion are held together in a network through hydrogen-bonding and electrostatic interactions. Each methylurea molecule, which is protonated, is stabilized via present strong hydrogen bonding with water molecules in the unit cell. Since this strong hydrogen bonding can play an important role in the formation of unique novelty of titled supramolecular network, we have carried out theoretical calculations on geometrical parameters, stabilization energies, and atomic charges based on natural bond orbital (NBO) analyses and then have compared with those of the neutral methylurea molecule. Our calculations have been done with the B3LYP method of density functional theory (DFT).     

Study of N,N′-dihydroxyethyldithiooxamide by X-ray diffraction,u.v.-vis,NMR, Raman and i.r. spectroscopy

The vibrational, NMR and electronic spectra of HO(CH₂)_xNHCSCSNH(CH₂)_xOH (x = 2,3,5,6) are discussed. A vibrational analysis has been proposed for the N,N′-dihydroxyethyldithiooxamide (x = 2) and its deuterated (NH/ND, OH/OD) analogue. The structure of N,N′-DHEDTO was solved by X-ray analysis. M_r = 208, monoclinic, space group P2₁/n, a = 9.8800(5) Å, b = 11.3260(7) Å, c = 9.7806(8) Å, β = 119.366(5)°, V = 953.8 ų, Z = 4, Dc = 1.365 Mgm⁻¹,μ(CuKα) = 0.47 mm⁻¹, F(000) = 440.00, T = 300 K. Final conventional R-factor = 0.036, R_w = 0.037, for 1608 unique reflections with I > 3.σ(I) out of 1800 measurements. The structure was solved using the automatic programs PATSYS and DIRDIF. The two νOH bands in the i.r. spectrum are in agreement with the crystallographic structure, which proposes that the unit cell of the compound consists of two independent molecules.     

Analysis of pigments and coverings by X-ray diffraction (XRD) and micro Raman spectroscopy (MRS) in the cemetery of Tutugi (Galera, Granada, Spain) and the settlement convento 2 (Montemayor, Córdoba, Spain)

This paper focuses on the identification of the composition of the coverings and pigments of two archaeological sites. The sites researched here lie in Andalusia and show two contexts, which have a highly symbolic and ritual meaning. The first, Convento 2 (Montemayor, Córdoba), dates back to the period of formation of the Iberian Culture (VIIth century b.c.). The second is the cemetery of Tutugi (Galera, Granada), of the mid-Iberian period (IVth century b.c.). The analytical procedure consisted in combined and complementary use of XRD and MRS. This allowed to identify the materials used, namely hematite, goethite, coal, gypsum and calcite. Identification of these materials proves essential for the restoration and musealization of both archaeological sites.     

Identification of complex anions in La1 − x A x MnO3 manganites (A = Ca, Sr) from neutron diffraction data and refinement of their structures on the basis of raman spectroscopy data

The consideration of the Mn(-O…Mn)₆ structure unit of the LaMnO₃ orthorhombic phase constructed on the basis of neutron diffraction data revealed the presence of atomic groups in the form of (MnO₂)^? complex anions and separate O^2? ions. The Raman spectra have demonstrated that complex anions have a nearly linear O=Mn-O^? structure. Comparison of the Raman spectra of the rhombohedral CaMnO₃ and BaTiO₃ phases and pyramidal molecules of the ZXY₂ type has shown that the CaMnO₃ phase is composed of pyramidal MnO ₃ ^2? molecules with one Mn=O double bond and two Mn-O^? ordinary bonds. The complex anions are linked by O=Mn-O^? intermolecular bonds to form planar zigzag Mn=O…Mn chains similar to C=C-C planar chains in some organic compounds exhibiting high electrical conductivity. With decreasing temperature, the Mn…O intermolecular distances decrease, and the Mn=O…Mn chains become even more similar to the C=C-C chains and exhibit high electrical conductivity.     

Solid state electrochemistry, X-ray powder diffraction, magnetic susceptibility, electron spin resonance, Mössbauer and diffuse reflectance spectroscopy of mixed iron(III)-cadmium(II) hexacyanoferrates

Coprecipitates of Cd^II, K^I and Fe^III with hexacyanoferrate ions [Fe(CN)₆]^4? have been studied by solid-state electrochemistry (voltammetry of immobilized microparticles), magnetic susceptibility measurements, X-ray powder diffraction, electron spin resonance, Mössbauer and diffuse reflectance spectroscopy. Most suprisingly, all experimental results point to the formation of a continuous series of complex mixed phases without the formation of phase mixtures. Although Cd^II and Fe^III ions differ too much in their ionic radii to allow the formation of simple substitution mixed hexacyanoferrates, they are capable of forming different kinds of complex insertion and substitution mixed crystals because of the zeolitic structure of both the iron and the cadmium hexacyanoferrate. Low cadmium concentrations can be found in the zeolitic cavities of iron hexacyanoferrate (Prussian blue), and they start to widen the lattice and facilitate, at higher concentrations, the direct substitution of high-spin iron(III) ions by cadmium ions. In cases of an excess of cadmium, the formation of cadmium hexacyanoferrate with iron(III) ions in the interstitials of the zeolitic structure is observed. These mixed phases show strong charge transfer bands in the visible range and have the appearance of “diluted” Prussian blue. For the first time, this indicates that the charge transfer between the carbon-coordinated low-spin iron(II) ions and the high-spin iron(III) ions can also occur when the latter are situated in the cavities of a host hexacyanoferrate. In Prussian blue the interstitial iron(III) ions are responsible for a very strong charge transfer interaction between the low-spin iron(II) ions and the nitrogen-coordinated high-spin iron(III) ions. Upon substitution of the very small amount of interstitial iron(III) ions in Prussian blue by potassium and cadmium ions the Kubelka-Munk function diminishes by more than 30%, indicating a tremendous decrease in iron(III)-iron(II) interaction.     

Synchrotron radiation total reflection X-ray fluorescence and energy dispersive X-ray fluorescence analysis on AP1™ films applied to the analysis of trace elements in metal alloys for the construction of nuclear reactor core components: a comparison

Synchrotron radiation induced total reflection X-ray fluorescence and conventional 45° energy dispersive X-ray fluorescence analysis using a 150-nm-thick AP1™ film as sample carrier have been exploited for the elemental analysis of traces in alloys used for the construction of reactor core components of nuclear power plants. Both techniques are well suited for the analysis since they require a low amount of sample (μl), important on one hand because of the limited disposal and on the other hand because of its high specific activity. The methods provide a very low background due to the total reflection phenomenon in TXRF and the thin AP1™ film sample support, respectively. The employment of synchrotron radiation was necessary since there are no laboratory sources which can deliver a collimated beam of the energy and intensity needed to excite the K-shell of the rare earth elements, allowing the achievement of minimum detection limits relevant for the proposed purpose (ng/g range). Moreover, the linear polarization of synchrotron radiation combined with a side-looking detection geometry manages to reduce the scattering due to the remaining matrix of the analyzed samples. Detection limits for Nb and for some of the rare earth elements (pg range for absolute detection limits and ng–μg/g range for concentration detection limits) obtained with the two techniques are presented and the two approaches are compared.     

Molecular and supramolecular properties of a Hg(II) complex with (E)-N,N′-bis(2-pyridyl)iminoisoindoline: synthesis,spectroscopy, X-ray structure and Hirshfeld surface analyses,and DFT calculations

A scarcity of metal complexes containing (E)-N,N′-bis(heteroaryl)iminoisoindolines has prompted us to investigate the coordinating ability and supramolecular behavior of (E)-N,N′-bis(2-pyridyl)iminoisoindoline (2-pyimiso), a versatile iminobis(pyridyl) ligand. The 1:1 reaction of HgCl₂ with 2-pyimiso in MeOH afforded a dinuclear complex, [{HgCl(2-pyimiso)}₂(μ-Cl)₂] (1). The complex has been characterized by elemental microanalysis, vibrational spectroscopy (FTIR and FT-Raman) and ¹H NMR spectroscopy. DFT calculations at the B3LYP-D3/LACV3P** level have been used in support of our vibrational analysis. Single-crystal X-ray diffraction data have shown that the coordination geometry of 1 is intermediate between the trigonal pyramidal and seesaw shapes insofar as each Hg(II) is four-coordinate and 2-pyimiso is a monodentate ligand. X-ray structure and Hirshfeld surface analyses have revealed that the supramolecular arrangement of 1 comprises perpendicular 1-D chains along the [011] direction assembled by nonclassical C–H?Cl–Hg and C–H?π hydrogen bonds. Moreover, adjacent sheets parallel to the bc-plane are interconnected by C–H?N_py, π–π_py stacking, and Hg?π_py interactions.     

Structural and vibrational characterization of [KrF][AuF6] and α-[O2][AuF6] using single crystal X-ray diffraction, Raman spectroscopy and electron structure calculations

The salt [KrF][AuF₆] has been prepared by the direct oxidation of gold powder in anhydrous HF at 20 °C using the potent oxidative fluorinating agent KrF₂. The KrF⁺ salt readily oxidizes molecular oxygen at ambient temperature to yield [O₂][AuF₆]. Variable temperature Raman spectroscopy has been used to identify a reversible phase transition in [O₂][AuF₆], which occurs between −114 and −118 °C. Single crystal X-ray diffraction has been used to characterize the low-temperature, α-phase of [O₂][AuF₆]. The phase transition is attributed to ordering of the O₂⁺ cation in the crystal lattice, which is accompanied by minor distortions of the AuF₆⁻ anion. The α-phase of [O₂][AuF₆] crystallizes in the triclinic space group , with a=4.935(6) Å, b=4.980(6) Å, c=5.013(6) Å, α=101.18(1)°, β=90.75(2)°, γ=101.98(2)°, V=342.97 Å³, Z=1, and R₁=0.0481 at −122 °C. The structure of the precursor, [KrF][AuF₆], has also been determined by single crystal X-ray diffraction and crystallizes in the monoclinic space group Cc with a=7.992(3) Å, b=7.084(3) Å, c=10.721(4) Å, β=105.58(1)°, V=584.8(4) Å³, Z=4 and R₁=0.0389 at −125 °C. The KrF⁺ and AuF₆⁻ ions interact by means of a FKr---FAu fluorine bridge that is bent by 125.3(7)° about the bridge fluorine. The KrF_t and Kr---F_b bond lengths in [KrF][AuF₆] were determined to be 1.76(1) and 2.15(1) Å, respectively. The energy minimized structures of the [KrF][AuF₆] ion-pair and the AuF₆⁻ anion have been determined at the Hartree-Fock (HF), MP2 and local density functional (LDF) levels of theory. These calculations have also been used to assign the vibrational spectrum of the [KrF][AuF₆] ion-pair in greater detail and to reassign the vibrational spectrum of the AuF₆⁻ anion.     

The lp(O)...π-interactions in 1-[1-(methoxycarbonylmethylthio)methyl]-3,5-dimethylisocyanurate: topological analysis of the electron density distribution from X-ray diffraction data and quantum chemical calculations

The intra- and intermolecular interactions that make a major contribution to the formation of the crystal structure were detected and characterized in the crystal of 1-[1-(methoxycarbonylmethylthio)methyl]-3,5-dimethylisocyanurate. Topological analysis of the experimental and theoretical electron density distribution was used to reveal for the first time the role of the lp(O)...π interaction in the formation of a crystal of an isocyanurate derivative and to estimate its energy. Interactions of this type were found to occur in 74% of the fully N-substituted isocyanurate structures.     

Simultaneous determination of germanium,arsenic, tin and antimony with total-reflection X-ray fluorescence spectrometry using the hydride generation technique for matrix separation—first steps in the development of a new application

This paper introduces a new perspective for total-reflection X-ray fluorescence analysis (TXRF), that is the simultaneous determination of Ge, As, Sn and Sb in seawater. As is well known from atomic absorption spectroscopy (AAS) and inductively coupled plasma techniques (ICP) compounds of these elements can be reduced by sodium borohydride to their hydrides and thus separated from the matrix. In this work the hydride generation is used for matrix separation in TXRF measurements. For this purpose the following procedures are considered: (1) Preconcentration of hydrides by absorption in solvents, and evaporation of some μl of this solution on the sample carrier. (2) Decomposition of hydrides in a heated thin silica tube, or at rough and/or catalytically active surfaces, e.g. in adequately prepared columns, eluting of the species by acid and evaporation of some μl of this solution on the sample carrier. (3) Decomposition of hydrides directly on the surface of a heated silica sample carrier as a thin amorphous film. (4) Combustion of hydrides in the hydrogen flame and deposition of an elemental film on the sample carrier. Basically, all four ways have been tested and the results are promising. © 1997 Elsevier Science B.V.     

Investigation of substitution effects and the phase transition in type-I clathrates RbxCs8-xSn44□2 (1.3≤x≤2.1) using single-crystal X-ray diffraction, Raman spectroscopy, heat capacity and electrical resistivity measurements

The substitution of cations in Rb_xCs_8-xSn₄₄□₂(1.3≤x≤2.1) is reported. The compounds crystallize at room temperature in the space group adopting the type-I clathrate 2×2×2 superstructure with partly ordered framework vacancies (□), whereas at higher temperatures they transform to the primitive, more disordered modification (space group ). The guest atom distributions in the Sn cages on the Rb: Cs ratios is studied by means of single-crystal X-ray diffraction for Rb_2.1(1)Cs_5.8(1)Sn₄₄ at T=293 K (1), Rb_1.42(8)Cs_6.58(8)Sn₄₄ at T=293 K (2a), Rb_1.46(5)Cs_6.54(5)Sn₄₄ at T=373 K (2b) and Rb_1.32(8)Cs_6.68(8)Sn₄₄ at T=293 K (3). The structural order-disorder phase transition influences the electrical resistivity. The hysteresis observed for the electrical resistivity in combination with the symmetric shape of the specific heat anomaly suggests that the transformation is of first-order type and is characterized by an entropy change of about 2.5 J mol^-1 K^-1. The Raman spectrum for the low-temperature modification of 2 is also reported.     

Structure of a zinc(II) N,N’-ethylene-bis (acetylacetoniminate) molecule,ZnO<Subscript>2</Subscript>N<Subscript>2</Subscript>C<Subscript>12</Subscript>H<Subscript>18</Subscript>, according to gas electron diffraction data and quantum chemical calculations

Gas electron diffraction is used to study the structure of a zinc(II) N,N’-ethylene-bis(acetylacetoniminate) molecule, ZnO₂N₂C₁₂H₁₈, at a temperature T = 503(5) K. It is found that the molecule has the symmetry of the C₂ equilibrium configuration with a nonplanar structure of the ZnN₂O₂ coordination fragment and internuclear distances r_h1(Zn-O) of 1.958(13) ? and _h1(Zn-N) of 2.012(16) ?. Quantum chemical calculations by the DFT/B3LYP/CEP,TZV method gives the molecular structure consistent with that found in the experiment.