Infrared study of the hydrogen bonding site in a poly-functional schiff base: N(sp2) or N(sp)?

The hydrogen bond complexes between phenol derivatives and the Schiff base [(diphenylmethylene)amino]-acetonitrile have been studied by infrared spectroscopy in carbon tetrachloride solution. The thermodynamic data and the infrared spectra investigated in the ν_OH, ν_CN and ν_CN region indicate that complex formation occurs at the nitrogen atom of the nitrile function. The hydrogen bonding site is in this case governed by the accessibility of the lone pair which is markedly higher for the N(sp) than the N(sp²) electrons.     

Near infrared absorption spectrum of perfluoro-t-butanol/acetonitrile complexes at low temperatures: Fermi resonances and simultaneous transitions

Interactions between perfluoro-t-butanol (PFTB) and acetonitrile-d₃ (AN) in a mixture of freons are studied between 298 and 88 K in liquid or vitreous states. In the conditions of the experiment, a mean 1:2 stoichiometry [PFTB⋯(AN)₂] is inferred from previous matrix measurements. A ν_OH shift of about 160 cm⁻¹ is observed in this temperature range: it is mainly ascribed to solvent effects on the complex. In fact, the dν_OH/dT coefficient increases at low temperature on account of specific solvation of the complex by the freon Br atoms. The ν_OH + τ_OH combination wavenumber is little dependent on the state of PFTB, near 3900 cm⁻¹. A comparatively strong simultaneous transition involving the PFTB ν_OH mode and a ν_CN mode of neighbouring AN molecules is observed. Weaker bands could also be explained by such transitions involving a combination level of PFTB and a ν_CN vibration. Strong Fermi resonances are displayed in the 2ν_OH region when the ν_OH band is located around 3100 cm⁻¹, either in pure AN or in freons at low temperature. The levels interacting with 2ν_OH are ternary combinations and quaternary overtones mainly involving the COH bend and the CO stretch. These resonances are favoured by a strong increase of the OH stretching vibration anharmonicity.     

Hydrogen bonds in solid hydroxides, a bond valence approach

The bond valences s_OH due to the O-H bonds of OH⁻ ions in solids have been calculated indirectly from intermolecular H?O distances, viz. those within the Wigner Seitz cell around the respective hydrogen atom, by using the equation s_OH=1−∑s_H?O. The bond valences thus derived are an excellent measure of the strength of O-H bonds [J. Mol. Struct. 351 (1995) 205]. This is shown by their almost linear correlation with the wave numbers of the stretching modes of matrix isolated OD⁻ ions observed with IR or Raman experiments. In the case of very weak or lacking hydrogen bonds, this correlation fails because then other interionic bonding phenomena than hydrogen bonds as metal-oxygen interactions and hydrogen-hydrogen repulsion etc. gain in importance or dominate finally and, hence, partly or fully determine the wave numbers of the OD stretching modes, which, however, still remain a measure of the respective bond strengths. The relation of the distances r_OH, the bond valences s_OH, and the stretching modes ν_OD of both free, gaseous OH⁻ ions and H₂O molecules and those embedded in crystalline matrices is discussed.     

pH‐Dependent Degradation of Layered Black Phosphorus: Essential Role of Hydroxide Ions

The practical application of layered black phosphorus (LBP) is compromised by fast decomposition in the presence of H₂O and/or O₂. The role of H₂O is controversial. Herein, we propose a hydroxide ion (OH^?)‐initiated degradation mechanism for LBP to elucidate the role of H₂O. We found that LBP degraded faster in alkaline solutions than in neutral or acidic solutions with or without O₂. Degradation rates of LBP increased linearly from pH 4 to 10. Density functional theory (DFT) calculations showed that OH^? initiated the decomposition of LBP through breaking the P?P bond and forming a P?O bond. The detection of hypophosphite, generated from OH^? reacting with P atoms, confirmed the hypothesis. Protons acted in a way distinctive from OH^?, by inducing deposition/aggregation or forming a cation–π layer to protect LBP from degradation. This work reveals the degradation mechanism of LBP and thus facilitates the development of effective stabilization technologies.     

Self-assembled tetrameric H2O clusters in the crystal lattice of [Cu(μ2-OH){Ph2P(O)NP(O)Ph2-κ1O,O′}(1,10-phen-κ2N,N′)]2·2H2O

Abstract

The synthesis and characterization of the dinuclear Cu(II) complex [Cu(μ²-OH){Ph₂P(O)NP(O)Ph₂-κ¹O,O′}(1,10-phen-κ²N,N′)]₂·2H₂O (1), 1,10-phen?=?1,10-phenanthroline, is described. X-ray crystallographic studies reveal that the Cu(II) centers of 1 are bridged by two OH^? groups and are coordinated by the (O,O)?= Ph₂P(O)NP(O)Ph₂^? ligand in a monodentate fashion, unprecedented for Cu(II). The crystal lattice of 1 also contains H₂O molecules, which are involved in the formation of a hydrogen bonding network with bridging OH^? groups and noncoordinated O atoms of the (O,O) ligand. These H₂O molecules are arranged in the crystal lattice of 1 as tetrameric clusters. The packing of molecules in the structure of 1 was investigated by Hirshfeld Surface analysis.     

Iron catalyzed demethylation of acetic acid*

Abstract

The iron(IV)-oxo catalyzed cleavage of acetic acid is reported. Iron(II) complexes are used as catalyst precursors and H₂O₂ as oxidant in reactions in aqueous solution with an excess of chloride and, in some experiments, with ascorbic acid added as an OH^. radical scavenger. It is shown that the acetic acid is cleaved into CO₂ and a methyl radical. In the presence of O₂ and OH^. radicals, the initially generated methyl radicals produce methanol and formate. Halogenated alkanes are also formed and, in the absence of O₂ and OH^. radicals, methane is obtained as the major product. A mechanism for the formation of various environmentally important volatile C₁ compounds is deduced from the present results and published studies, and its relevance as an additional source for these compounds in the atmosphere is discussed.     

IR Spectrum and Structure of Protonated Monosilanol: Dative Bonding between Water and the Silylium Ion

We report the spectroscopic characterization of protonated monosilanol (SiH₃OH₂⁺) isolated in the gas phase, thus providing the first experimental determination of the structure and bonding of a member of the elusive silanol family. The SiH₃OH₂⁺ ion is generated in a silane/water plasma expansion, and its structure is derived from the IR photodissociation (IRPD) spectrum of its Ar cluster measured in a tandem mass spectrometer. The chemical bonding in SiH₃OH₂⁺ is analyzed by density functional theory (DFT) calculations, providing detailed insight into the nature of the dative H₃Si⁺‐OH₂ bond. Comparison with protonated methanol illustrates the differences in bonding between carbon and silicon, which are mainly related to their different electronegativity and the different energy of the vacant valence p_z orbital of SiH₃⁺ and CH₃⁺.     

SYNTHESIS AND CHARACTERIZATION OF NEW OXODIPEROXOVANADATE COMPLEXES CONTAINING COORDINATED AMINOACIDS

Abstract

The study of peroxovanadium compounds has received renewed attention since the discovery of their insulin mimetic properties and of the vanadium bromoperoxidase enzyme which catalyzes the oxidation of halides by hydrogen peroxide. This work presents the synthesis and characterization of three novel oxodiperoxovanadium complexes, K _n [VO(O₂)₂AA] 2H₂O, where AA = L-asparagine(l), L-phenylglycine(2), D, L-homocystine(3). The products were synthesized by the reaction of V₂O₅, with the amino acid and H₂O₂ at room temperature. The compounds obtained are yellow, soluble in water and insoluble in organic solvents. They show remarkable hygroscopic character and are light and temperature sensitive. IR and UV-VIS spectra of the compounds show the typical oxo and diperoxo bands (ν_v = o = 970 cm^?1, ν_vo-o = 870cm^?1, νv-O₂ = 630, 525 cm^?1, ? ?320nm). The ligand bonding properties were determined on the basis of electric conductivity and spectroscopic data (IR, ¹H NMR) as well as elemental analysis.     

O-H bond dissociation energies in hydroquinones and 4-hydroxyphenoxyl radicals and effect of solvation on the kinetics of reactions involving hydroquinones and semiquinone radicals

The O-H bond dissociation energies (D _OH) in the molecules of 2,5-dimethylhydroquinone (1) and 2,5-di-tert-butylhydroquinone (2) and in the corresponding semiquinone radicals (5 and 8, respectively) were estimated by the method of intersecting parabolas (IP) from experimental data on the rate constants for the reactions of these compounds with N-phenyl-1,4-benzoquinonemonoimine (3) and using the density functional B3LYP/6-31+G* quantum chemical calculations. When calculating the D _OH values by the IP method, solvation of reactants and transition states should be taken into account. The energies of solvation of quinones, semiquinone radicals, and hydroquinones were evaluated by the PCM method. The results of quantum chemical calculations obtained with inclusion of the effects of solvation and the D _OH estimates obtained by the IP method are in good agreement, being equal to 337.9±1.6, 242.5±1.4, and 242.7±3.4 kJ mol⁻¹ for molecule 1 and radicals 5 and 8, respectively. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2244–2251, October, 2005.     

Mechanochemical Synthesis of Phosphates and Phase Transformations of Natural Apatites by Mechanical Action

Abstract

The mechanochemical method is a promising way of synthesizing new and complicate phosphorus compounds and processing phosphate rocks in order to obtain the fertilizers. Apatites with general compositional formula-Me₁₀(RO₄)₆Z₂, Ca²⁺, Ba²⁺, Cu²⁺, Pb²⁺, Mn²⁺, Fe²⁺, A1³⁺; RO₄ -PO^3- ₄, Co^2- ₃, Alo^? ₂, Sio^4- ₄, So^2- ₄, Zro^4- ₄; z-F^? F^?, OH^?, cl^?, CO^2- ₃, O^? S^2-, HCOO^? and isomorphous mixtures by mechanical action in planetary mill at room temperature were synthesized. Duration of the synthesis varied from 5 min. to 30 min. The initial components for synthesis were phosphates, oxides, chemical elements (Si, S, Al, Cu, Pb, Fe) and organic compounds. The synthetic apatites are promising materials for the production of bioceramic, catalysts, ion-exchangers and laser glasses.     

First‐principles calculation of OH−/OH adsorption on gold nanoparticles

The OH^? and OH adsorption structures on Au₅₅ and Au₁₃ nanoparticles surfaces are analyzed using density functional theory. The most stable OH^? adsorption site of Au₅₅ and Au₁₃ nanoparticles is found to be the vertex top site followed by the (111)‐(100) edge bridge site. On the contrary, the stability order of OH adsorption is opposite to that of OH^?. The adsorption of OH^? is calculated to be weaker than that of OH, which shows different charge transfer and interactions with gold surface. Coadsorption on nanoparticles is studied to find that multiple OH^? species prefer the most stable sites of single OH^? adsorption. The hydrogen bonding between adsorbed OH^? on gold surface is a key factor in stabilizing the adsorbates on the Au surface. © 2015 Wiley Periodicals, Inc.     

Structural and spectroscopic investigations on Eu3+-doped alkali fluoroborate glasses

Eu³⁺-doped alkali fluoroborate glasses B₂O₃–XCO₃–NaF–Eu₂O₃ (where X = Li₂, Na₂, K₂, and Ca, Mg) have been prepared using the conventional melting technique and their structural and optical properties have been evaluated. The XRD pattern of the glasses confirmed the amorphous nature and the FTIR spectra reveal the presence of BO₃ and BO₄ units as their local structures along with the strong OH^? groups. From the absorption spectra the bonding parameters have been calculated and confirmed that the Eu–O bonds in the studied glasses are of covalent nature. Judd–Ofelt (JO) analysis has been carried out from the emission spectra. The JO parameters have been used to calculate transition probabilities (A), lifetime (τ_R) and branching ratios (β_R) and peak stimulated emission cross-section (σ_P^E) for the ⁵D₀ → ⁷F_J (J = 1, 2, 3 and 4) transitions of the Eu³⁺ ions. The decay from the ⁵D₀ level of Eu³⁺ ions in the title glasses has been measured and analysed. The lifetime of the ⁵D₀ level is found to be shorter than the reported glasses which may be due to the presence of OH^? groups.     

Nicotinamide complex of silver(III) with expanded coordination number

Abstract

In strongly alkaline media ([OH^?]?≥?0.12 M), nicotinamide (nica) forms a complex with square-planar Ag(OH)₄^? [nica]?≥?0.05 M. The complex decomposes in seconds to nicotinamide N-oxide. The correlation of maximum absorbance of the complex with concentrations of nicotinamide and hydroxide requires that the complex is either the five-coordinate Ag(OH)₄(H_-1nica)^2? or the six-coordinate Ag(OH)₅(nica)^2?. Comparison with the reactions of Ag(OH)₄^? with nicotinate ion (nic^?) and acetamide under similar conditions indicates that nicotinamide coordinates with Ag(OH)₄^? by the amido group rather than the nitrogen on the pyridine ring or the amido oxygen. Kinetics of the Ag(III)-nica redox reaction are consistent with direct reaction between nicotinamide and uncoordinated Ag(OH₄)^?. Oxidation takes place at the pyridine ring, yielding nicotinamide N-oxide. Silver(III) is reduced to monovalent silver.     

Heterobinuclear and Heterotrinuclear complexes of Oxorhenium(V) with Cu(II), Ni(II), Fe(III), UO2(VI) and Th(IV) in the solid state

New heteronuclear complexes containing oxorhenium(V), Cu(II), Ni(II), Fe(III), UO₂(VI) and Th(IV) ions were prepared by the reaction of the complex ligand, [ReO(H₄L)Cl]Cl₂, where H₄L = 8,17-dimethyl-6,15-dioxo-5,7,14,16-tetrahydrodibenzo[a,h][14]annulene-2,11-dicarboxylic acid, with the previous transition and actinide salts. Three heteronuclear Cu(II) complexes were isolated depending on the ratio of [ReO(H₄L)Cl]Cl₂?:?Cu(II) ion. When the ratios were 1?:?0.5, 1?:?1 and 1?:?2, the heteronuclear complexes {[ReO(H₃L)Cl]₂CuCl₂(OH₂)₂}SO₄ · H₂O (I), [ReO(H₃L)Cl₂Cu(OH₂)₂(SO₄)] (II) and {ReO(H₂L)Cl[Cu(OH₂)₃ SO₄]₂} (III) were obtained, respectively. Heteronuclear complexes of the other metal cations were obtained by mixing [ReO(H₄L)Cl]Cl₂ with the metal salt in the ratio 1?:?1 to obtain the heteronuclear complexes [ReO(H₃L)Cl₂Ni(OH₂)₂](NO₃)₂ (IV), [ReO(H₃L)Cl₃Fe(OH₂)₃](NO₃)₂ (V), [ReO(H₃L)ClUO₂(NO₃)₂ (OH₂)]Cl (VI) and [ReO(H₃L)Cl₃Th(NO₃)₂(OH₂)]NO₃ · 2H₂O (VII). The complex ligand coordinates with the heterometal ion via the carboxylate group, and the infrared bands ν_as COO and ν_s COO indicate that the carboxylate acts as a unidentate ligand to the heterometal cations. Cu(II) and Fe(III) cations in the heteronuclear complexes have octahedral geometry, while Ni(II) is square planar. Thermal studies explored the possibility of obtaining new heteronuclear complexes pyrolytically in the solid state from the corresponding mother complexes. The structures of the complexes were elucidated by conductance, IR and electronic spectra, magnetic moments, ¹H NMR and TG-DSC measurements as well as by mass spectroscopy.     

Thermal, magnetic and spectral properties of metal quinone complexes

The reactions of 3-chloro-2-hydroxy-1,4-naphthoquinone; chlorolawsone with “Na” metal (ClLw-1), CH₃COONa (ClLw-2), NaOH (ClLw-3), KOH (ClLw-4) and K₂CO₃ (ClLw-5) have been studied. Dark brown solids obtained for ClLw-1 to ClLw-5 are characterized by elemental analysis FTIR, ¹HNMR, UV–Visible spectroscopy, thermogravimetric analysis and DSC studies. FTIR of ClLw-1 to ClLw-5 shows decrease in ν_C=O frequency after complexation of alkali metal ions and ν_OH of adsorbed as well as coordinated water molecules have been observed between 3,600 and 3,100 cm^?1. The benzenoid protons C(5)H and C(8)H shows down field shift due to intermolecular hydrogen bonding interaction with neighboring molecules and upfield shift have been observed for C(6)H and C(7)H protons in ClLw-1 to ClLw-5 in ¹HNMR spectra. Bathochromic shift ~2 to ~5 nm have been observed for band at 287 nm. The nature of pyrolytic decomposition in chlorolawsone anion in ClLw-1 to ClLw-5 has been observed to be “gradual-1–abrupt–gradual-2”. Phase transition occurred during gradual-1 pyrolytic decomposition of chlorolawsone anion in ClLw-1 to ClLw-4 has been studied by DSC.     

A new tetranuclear copper(II) complex containing decameric water clusters bridged by–OH–and pyridine-2,4, 6-tricarboxylate: synthesis and magnetic characterization

Using pyridine-2,4,6-tricarboxylic acid (H₃ptc) and 2,2-bipyridine (2,2-bipy), a tetranuclear copper(II) compound [Cu₄(2,2-bipy)₄(ptc)₂(H₂O)₂(OH)₂] · 12H₂O (1) has been isolated under hydrothermal conditions. Variable temperature magnetic susceptibility of 1 from 2–300 K indicates anti-ferromagnetic interactions. The magnetic exchange coupling constants of J = ?159.4 and J′ = ?18.66 cm^?1 for 1 can be obtained through fit of the magnetic data, corresponding to two kinds of bridges, hydroxyl anions (OH^?) and pyridine carboxylate oxygen of ptc^3?. Moreover, decameric water clusters can also be observed, which are located between these tetranuclear copper(II) entities, forming a series of intricate O-H ··· O hydrogen bonds and stabilizing the resulting three-dimensional (3-D) hydrogen-bonded framework structure.     

PREPARATION AND CRYSTAL STRUCTURE OF THE HOST-GUEST TYPE COMPLEX OF TRIS(BIPYRIDINE)NICKEL(II)-TETRAKIS(CYANO) NICKELLATE (II))-HEXAHYDRATE-HEMI (BIPYRIDINE)

Abstract

The title complex is built up of [Ni(bpy)₃]²⁺ cations, [Ni(CN)₄]^2? anions and non-coordinated bpy and water molecules. The water molecules along with one of the two crystallographically independent tetracyanonickellate anions form layers, in which H-bonds (HB's) of the types O-H ‥ O and O-H ‥ N are important. The remaining tetracyanonickellate anions bound by H-bonds to water molecules in the layers are placed approximately perpendicular to the layers making interconnection between them. So by HBs a 3D network is formed (hydrophilic host part of the structure). The cations and non-coordinated bpy molecules (hydrophobic guest part of the structure) are placed in cavities formed by HBs. The Ni-N distances in the cation are within the range 2.078(3)-2.100(3) Å and the Ni-C distances in the anion are within the range 1.854(5)-1.873(4) Å.     

Preparation and Electrical Properties of Hydroxyapatite Containing Yttrium

Abstract

Hydroxyapatite (HAP) containing yttrium ion was synthesized and sintered for obtaining apatite ceramics with new functional properties. The preparation of the ceramics was carried out by synthesis using the wet process and by sintering under water vapor atmosphere. The product was recognized to be a solid solution. By substituting Y for Ca, O^2- and lattice defect (□) will form as follows: OH^? → O^2- + H₂O + □. Then, a following formula can be described for this solid solution produced:

Ca₁0-x^yx^(PO₄)2-x-2y^Ox+2y□y. The ionic conductivity of the product was measured by the ac two probe method. The plot.of conductivity-Y content relation gave a characteristic curve with a sharp peak at a fixed composition, Y=0.65. It was considered that this tendency was due to a change in the charge carrier in HAp crystal from OH- to H⁺ and O^2? with varying Y content. Electromotive force was observed in a water vapor cell assembled using the phosphate ceramics, and hydrogen gas generation was recognized. These phenomena led a fact that proton conduction exists in the ceramics. It was concluded that this ceramics will be used as a fuel cell.     

Structure of hexaaquamagnesium (II) bis(4-<Emphasis Type="Italic">p</Emphasis>-aminobenzenesulfamido-2,6-dimethoxypyrimidinate) pentahydrate

The X-ray analysis of a single crystal of Mg(C₁₂H₁₃N₄O₄S)₂·11H₂O, where (C₁₂H₁₃N₄O₄S)^? is the anion of 4-p-aminobenzenesulfamido-2,6-dimethoxypyrimidine (sulfadimethoxine) is carried out. Unit cell parameters are: a = 19.753(4) Å, b = 34.031(7) Å, c = 13.859(3) Å; β = 125.37(3)°, C2/c, Z = 8, R(F) = 0.042. The structure is built of [Mg(OH₂)₆]²⁺, (C₁₂H₁₃N₄O₄S)^?, and water molecules and corresponds to the formula [Mg(OH₂)₆](C₁₂H₁₃N₄O₄S)₂·5H₂O. The IR bands of ν_asymSO₂ and ν_symSO₂ are bathochromically shifted as a result of their participation in hydrogen bonding, and not because of any direct coordination of sulfadimethoxinate anion to the complexing atom through oxygen.     

On spectroscopic properties and isotope effects of vibrationally stabilized molecules

Results of quantum and semiclassical calculations obtained for two different potential-energy surfaces are used to discuss spectroscopic properties and isotope effects of the linear IHI and IDI molecules. The potentials are a purely repulsive LEPS surface and a DIM-3C potential with two van der Waals type minima for equivalent IH ··· I and I ··· HI configurations. Both systems are dominated by the effect of vibrational bonding giving rise to some very unusual spectroscopic phenomena, which are discussed in detail. The different vibrational frequencies and rotational constants are roughly estimated as ν₁ = 120 (100) cm^?1, ν₂ = 280 (210) cm^?1, ν₃ = 360 (160) cm^?1 and B = 0.0194 (0.0196) cm^?1 for IHI (IDI). A detailed discussion of the dependence of ν₁, ν₂ and B on ν₃, their sensitivity to variations of the potential-energy surface, and a comparison with the vibrational frequencies of I₂ and HI (ID) is given. It is predicted that there exists only one excited level of the antisymmetric stretching mode. The numbers of symmetrical stretching and bending levels are fairly constant or may even decrease upon deuteration. Simultaneously deuteration destabilizes the molecule. These unusual phenomena are rationalized by our calculations. A set of criteria for observing infrared and Raman bound-to-bound and bound-to-resonance state transitions are presented for the IHI and IDI molecule.