Ozone Activation on TiO2 Studied by IR Spectroscopy and Quantum Chemistry

The adsorption of different isotopic ozone mixtures on TiO2 at 77K was studied using FTIR spectroscopy and DFT calculations of cluster models. In addition to weakly bound ozone with band positions close to those of free or dissolved molecules, the spectrum of chemisorbed species was observed. The splitting of the ν1+3 combination band to eight maxima due to different isotopomers testified to the loss of molecule symmetry. The frequencies of all the isotopic modifications of the ozone molecules which form monodentate or bidentate complexes with four- or five-coordinated titanium atoms were calculated and compared with those of experimentally observed spectra. The four considered complexes adequately reproduced the splitting of the ν1+3 vibration band and the lowered anharmonism of chemisorbed O3. The energetically most favorable monodentate complex with four-coordinated titanium atoms showed good agreement with the observed spectra, although a large difference between the frequencies of ν1 and ν3 modes was found. For better coherence with the experiment, the interaction of the molecule with adjacent cations must be considered.

Influence of CO2 Molecules Adsorption on the Electronic Properties of Zigzag and Armchair ZnO Nanotubes

Here, the adsorption behavior of the CO2 molecules on electronic properties of zigzag and armchair ZnO nanotubes (ZnONTs) has been studied at M06-2X/6-31G(d) level of theory. It is found that CO2 molecules can be physically adsorbed on the nanotubes. Two minima structures A (monodentate) and B (bidentate) were found on the potential energy surface. Inspection of the results shows that in zigzag and armchair nanotubes, the monodentate complex is more stable than bidentate complex. Also, the stability of complexes increases by increasing the number of CO2 molecules. Comparison of adsorption energies shows that adsorption of CO2 molecules over zigzag (6, 0) model is stronger than armchair (4,4) model. In this work, the various parameters such as electronic chemical potential (m), hardness (ƞ), softness (S), the maximum amount of electronic charge (DNmax), electrophilicity index (ω), dipole moment and work function were investigated to evaluate the reactivity of structures. It is predicted that the conductivity and reactivity of nanotubes increase upon complexation. Based on the natural bond orbital (NBO) analysis, in all complexes charge transfer occurs from CO2 molecules to the nanotube. Theory of atoms in molecules (AIM) was also applied to characterize OCO2… Zn interaction in nanotubes. In addition, the interaction strength is studied through the reduced density gradient (RDG) function. It is predicted that the ZnONTs can be introduced as a favorable candidate in the design and construction of sensors for detecting CO2 molecules.

In-house and synchrotron X-ray diffraction studies of 2-phenyl-1,10-phenanthroline, protonated salts, complexes with gold(III) and copper(II), and an orthometallation product with palladium(II)

Different salts of the 2-phenyl-1,10-phenanthrolin-1-ium cation, (pnpH)+, are obtained by reacting 2-phenyl-1,10-phenanthroline (pnp), C18H12N2, (I), with a variety of anions, such as hexafluoridophosphate, C18H13N2+·PF6−, (II), trifluoromethanesulfonate, C18H13N2+·CF3SO3−, (III), tetrachloridoaurate, (C18H13N2)[AuCl4], (IV), and bromide (as the dihydrate), C18H13N2+·Br−·2H2O, (V). Compound (I) crystallizes withZ′ = 2, with both independent molecules adopting a coplanar conformation. In (II)–(IV), a hydrogen bond exists between the cation and anion, while one of the lattice water molecules serves as a hydrogen-bonded bridge between the cation and anion in (V). Reaction of (I) with HAuCl4gives the salt complex (IV); however, reaction with KAuCl4produces the monodentate complex trichlorido(2-phenyl-1,10-phenanthroline-κN10)gold(III), [AuCl3(C18H12N2)], (VI). Dichlorido(2-phenyl-1,10-phenanthroline-κ2N,N′)copper(II), [CuCl2(C18H12N2)], (VII), results from the reaction of CuCl2·2H2O and (I), in which the CuIIcenter adopts a tetrahedrally distorted square-planar geometry. The pendent phenyl ring twists to a bisecting position relative to the phenanthroline plane. The square-planar PdIIcomplex, bromido[2-(phenanthrolin-2-yl)phenyl-κ3C1,N,N′]palladium(II), [PdBr(C18H11N2)], (VIII), is obtained from the reaction of (I) with [PdCl2(cycloocta-1,5-diene)], followed by addition of bromine. A coplanar geometry for the pendent ring is adopted as a result of the tridentate bonding motif.

Copper Fixation to Guaiacyl Lignin Units by Nitrogen Donor Ligands

Several new copper(II) complexes with guaiacyl lignin models vanillin (HL1) [Cu(L1)2(nia)2] (1) (nia = nicotinamide) or vanillic acid (HL2) [Cu(L2)2(nia)2] (2) [Cu2(μ-L2)4(nia)2] (3), and [Cu(L2)2(Hetam)2] (4) (Hetam = ethanolamine) were isolated and characterized. The molecular structure of complex 1 reveals bidentate vanillin (HL1) coordination via the methoxy and the deprotonated hydroxy groups. On the other hand, the vanillic acid (HL2) complexes 2 - 4 show a deprotonated carboxylate group with chelating coordination mode in 2, bridging in 3 and monodentate coordination in 4. The mononuclear complexes 1, 2 and 4 show a distorted trans octahedral coordination sphere with pairs of monodentate and chelating ligands. A replacement of the monodentate nicotinamide ligand in 2 with the bidentate ethanolamine ligand in 4 changes the coordination mode of the vanillic acid anion from bidentate (complex 2) to monodentate (complex 4). This shift inside the coordination sphere reveals different O-Cu-O Jahn-Teller axes by the vanillic acid anion in 2 and ethanolamine in 4. Empty channels are present in the crystal structure of the dinuclear complex 3, stabilized by hydrogen bonds and π-π stacking.

Sorption of Molybdenum(VI) on Synthetic Magnetite

ABSTRACTIn this study we experimentally investigated the interaction of Mo(VI) with magnetite, which is a corrosion product of steel. The work was conducted with commercial magnetite, and we studied the influence of pH, pe and solid/liquid ratio on Mo sorption. A Surface Complexation Model (SCM) has been applied tothe experimental data, allowing to explain the results using the Diffuse Layer Model (DLM) and by considering the formation of the monodentate complex: >FeOMo(OH)5. At pH 2, experimental data were satisfactorily fitted to a a Langmuir isotherm.

Adsorption of Carboxylic Acids on Submicrocrystalline Aluminum Hydroxides in Aqueous Solution. Part I: Qualitative Study by Infrared and Raman Spectroscopy

Adsorption of acetic, oleic, benzoic, and salicylic acids on submicrocrystalline aluminum hydroxide samples is investigated in aqueous solutions. Experimental infrared and Raman spectroscopic data are analyzed to determine the reactivity of the monocoordinated hydroxyl groups located on the edge faces of bayerite or gibbsite crystals. Two key parameters were (1) the effect of concentration of aqueous solutions of the acids, and (2) the variation in specific surface areas of different samples of bayerite and gibbsite powders. Strong preferential adsorption to bayerite was observed over the whole pH range. No adsorption to gibbsite was detected. Data from the literature indicate that acetate, oleate, and benzoate form bidentate complexes on bayerite while salicylate forms a monodentate complex. The infrared spectra show that only monocoordinated hydroxyl groups are reactive, in the bayerite samples, and the band at 1020 cm−1 corresponds to the deformation mode of the monocoordinated hydroxyl groups whose stretching vibration was at 3465 cm−1. It is suggested that the specific surface areas given by the adsorption isotherms is a condition necessary for adsorption, but not sufficient in itself. Adsorption requires the presence of Al-OH2+1/2 species as well as the presence of steps or of a packaging sequence ABABABA rather than a packaging sequence ABBAABBA of the hydroxyl planes. The gibbsite impurity present in the bayerite sample reacted completely, while the lateral OH in the gibbsite sample did not, reflecting the lower reactivity in gibbsite relative to extended domains of bayerite.

Phosphato complexes of cobalt(III). II. Reversible chelation and ring-opening reactions

The bidentate phosphato complex Co en2PO40; has been shown to exist in rapid reversible equilibrium with the monodentate complex Co en2OH.HPO40 A detailed kinetic analysis of the opposed ring-opening and ring-closing (or chelation) reactions has evaluated rate constants for each of the protonated forms in acid and basic media. The ring-opening reaction is subject to both acid and base catalysis. However, within the pH range 6-9, the bidentate form containing a four-member phosphate ring is thermodynamically more stable than the monodentate form. This is ascribed to a rapid chelation reaction arising from a favourable cis hydrogen-bonded transition state.