theoretical study of tetrahydroborates and alanates L(MH4)4, HL(MH4)3, H2L(MH4)2, and H3L(MH4) (L = Al, Sc, Ti, V, Cr; M = B, Al)

The structural and energetic characteristics of the lowest-lying structures for isolated molecules and ions of light-metal boro- and aluminohydrides L(MH₄)₄, HL(MH₄)₃, H₂L(MH₄)₂, and H₃L(MH₄) (L = Al, Sc, Ti, V, Cr; M = B, Al) with different coordination modes of BH₄⁻- and AlH₄⁻ groups were calculated by the perturbation theory (MP₂), coupled cluster (CCSD(T)), and density functional theory (B3LYP) methods using the 6-31G*, 6-311+G**, and 6-311++G** basis sets. The results are compared with the computational data obtained at the same level of theory for related complexes L(MH₄)₃, HL(MH₄)₂, H₂L(MH₄), L(MH₄)₂, and HL(MH₄). The preferable coordination modes of the ligands in these complexes are analyzed, and the energies of dissociation with elimination of BH₃ (AlH₃) molecules and BH₄⁻ (AlH₄⁻) anions in various series of related hydroborates and hydroaluminates are estimated. The structure and relative stability of classical hydride and (μ-H₂)-hydrogen complexes in the H₂L (MH₄)₂ and H₃L(MH₄) systems are discussed. Original Russian Text ? O.P. Charkin, 2009, published in Zhurnal Neorganicheskoi Khimii, 2009, Vol. 54, No. 6, pp. 1015–1024.     

Comparison of Partial Least Squares Regression and H-Point Standard Addition Method for Simultaneous Spectrophotometric Determination of Zinc, Cobalt and Nickel by 1-(2-Pyridylazo)2-Naphthol in Micellar Media

Simultaneous spectrophotometric methods are described for the determination of Zn²⁺, Co²⁺ and Ni²⁺ by 1-(2-pyridylazo)2-naphthol (PAN) in micellar media, using absorbance correction-H-point standard addition method (HPSAM) and partial least squares (PLS) regression. The ligand and its metal complexes, i.e. Zn²⁺-PAN, Co²⁺-PAN and Ni²⁺-PAN, were made water-soluble by the neutral surfactant Triton X-100, and therefore extraction with organic solvents was no longer required. Formation of all of these complexes was complete within 10min at pH 9.2. The linear range was 0.1–1.5mgL^–1 for Zn²⁺, 0.1–2.0mgL^–1 for Co²⁺ and 0.1–2.0mgL^–1 for Ni²⁺. The relative standard deviation (RSD) for the simultaneous determination of 0.50mgL^–1 each of Zn²⁺, Ni²⁺ and Co²⁺ by applying the H-point standard addition method was 2.55%, 2.04% and 3.70%, respectively. The total relative standard error for applying the PLS method to 9 synthetic samples in the linear ranges of these metals was 1.8%. Interference effects of common anions and cations were studied, and both methods were applied to the simultaneous determination of Zn²⁺, Co²⁺ and Ni²⁺ in alloy samples.     

Quantum chemical study of the coordination of glycolic acid conformers and their conjugate bases to [Ca(OH2)n] (n=0–4) ions

A detailed exploration of the configurational and conformational space of glycolic acid and their conjugate bases has been carried out with the aid of first principles quantum chemical techniques at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory. The most stable configuration among the eight possible glycolic acid conformers corresponds to the E-s-cis, s-trans configuration, while the highest energy E-s-trans, s-cis conformer was found at 10.88 and 12.17 kcal mol⁻¹ higher in energy at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory, respectively. Upon dissociation of glycolic acid the s-cis(syn), and s-trans(anti) configurations of the glycolate anion can be formed. The anti conformer was found to be less stable than the syn one by 14.20 and 16.87 kcal mol⁻¹ at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p)) levels of theory, respectively. The computed B3LYP/6-311+G(d,p) proton affinity of the syn conformer for the protonation process affording the more stable E-s-cis, s-trans conformer, in vacuum was found to be 325.35 kcal mol⁻¹ (ΔG⁰ value). From a methodological point of view, our results confirm the reliability of the integrated computational tool formed by the B3LYP density functional model. This model has subsequently been used to investigate the interaction of Ca²⁺ ions with the glycolic acid conformers and their conjugate bases in vacuum and in the presence of extra water ligands. For the complexes of glycolic acid conformers the η²–O,O–(COOH) coordination, that is the structure that arises from the coordination of the Ca²⁺ to the carboxylic group, is the global minimum of the PES, while the η²–O(OH),O–(COOH) coordination is a local minimum found at only 1.0 and 1.3 kcal mol⁻¹ higher in energy at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory, respectively. Moreover, the two isomers exhibit nearly the same binding affinities, which are predicted to be 89 and 85 kcal mol⁻¹ at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory, respectively. The same holds also true for the complexes of the glycolate anion. The η²–O,O–(COO⁻) coordination involving the syn conformer of the glycolato ligand, is the global minimum, while the η²–O(OH),O–(COO⁻) one lies at 1.5 and 5.6 kcal mol⁻¹ higher in energy at the B3LYP/6-311+G(d,p) and CCSD(T)/6-31G(d,p) levels of theory, respectively. The other conformer with an η²–O,O–(COO⁻) coordination involving the anti conformer of the glycolato ligand, is less stable by only 0.2 kcal mol⁻¹ at both levels of theory. Noteworthy is the trend seen for the incremental binding energy due to the successive addition of water molecules to [HOCH₂C(O)O]Ca²⁺ species; the computed values are 30.4, 26.8, 22.9 and 16.2 kcal mol⁻¹ at the B3LYP/6-311+G(d,p) level of theory for the mono-, di-, tri- and tetraaqua complexes, respectively. This trend arising from the repulsion of the dipoles between the water ligands and from unfavorable many body interactions is in accordance with those anticipated from electrostatic considerations. The Ca(II)-water interaction weakens with increasing coordination of the metal. Obviously, it is the electrostatic nature of the Ca(II)-water interactions that accounts well for the computed coordination geometries of the cationic (aqua)(glycolato)calcium complexes. Calculated structures, relative stability and bonding properties of the conformers and their complexes with [Ca(OH₂)_n]²⁺ (n=0–4) ions are discussed with respect to computed electronic and spectroscopic properties, such as charge density distribution, harmonic vibrational frequencies and NMR chemical shifts.     

Iminopropadienones R–NCCCO and carbon suboxide, C3O2. Theoretical and experimental C NMR spectra

The ¹³C NMR data of five iminopropadienones R–NCCCO as well as carbon suboxide, C₃O₂, have been examined theoretically and experimentally. The best theoretical results were obtained using the GIAO/B3LYP/6-31+G**//MP2/6-31G* level of theory, which reproduces the chemical shifts of the iminopropadienone substituents extremely well while underestimating those of the cumulenic carbons by 5–10 ppm. The computationally faster GIAO/HF/6-31+G**//B3LYP/6-31G* level is also adequate.     

以[M(DETA)2)]n+(M=Cu2+, Ni2+, Co3+)为客体的MnPS3夹层化合物的合成、结构表征与磁性研究

将过渡金属配合物阳离子([M(DETA)₂]ⁿ⁺(M=Cu²⁺,Ni²⁺,Co³⁺;DETA=Diethylenetriamine,二乙烯三胺)作为客体插入层状MnPS₃层间得到了相应的3个夹层化合物。通过X-射线粉末衍射、元素分析和红外光谱对夹层化合物的结构进行了表征。结果表明,与主体MnPS₃ 0.65 nm的层间距相比较,夹层化合物(Mn_0.88PS₃[Cu(DETA)₂]_0.12)的层间距扩大了0.32 nm,由此推测客体[Cu(DETA)₂]²⁺在层间以平面四方的配位形式存在,而另2个夹层化合物(Mn_0.79PS₃[Ni(DETA)₂]_0.21和Mn_0.74PS₃[Co(DETA)₂]_0.17)的层间距扩大了0.48 nm,说明客体[(M(DETA)₂]ⁿ⁺,M=Co³⁺,Ni²⁺) 在主体层间以八面体配位形式存在。磁性测试结果表明过渡金属离子[(M(DETA)₂]ⁿ⁺(M=Cu²⁺,Co³⁺)的插入能引起主体MnPS₃的磁性在35~40 K发生由顺磁向亚铁磁性的转变并表现自发磁化,而客体[Ni(DETA)₂]²⁺却使夹层化合物的反铁磁相互作用增强,抑制了自发磁化的发生。     

Catalyzed Peptide Bond Formation in the Gas Phase. Role of Bivalent Cations and Water in Formation of 2-Aminoacetamide from Ammonia and Glycine and in Dimerization of Glycine

The formation of 2-aminoacetamide from ammonia and glycine and N-glycylglycine from two glycine molecules with and without Mg²⁺, Cu²⁺, and Zn²⁺ cations as catalysts have been studied as model reactions for peptide bond formation using the B3LYP functional with 6–311+G(d,p) and 6–31G(d) basis sets. The B3LYP method was also used to characterize the nine gas–phase complexes of neutral glycine, its amide (2-aminoacetamide), and N-glycylglycine with Lewis acids Mg²⁺, Cu²⁺, and Zn²⁺, respectively. Further, the gas-phase hydration of metal-coordinated complexes of glycine, 2-aminoacetamide, and N-glycylglycine was also investigated. Finally, the effect of water on the structure and reactivity of the metal coordinated complexes was determined. Enthalpies and Gibbs energies for the stationary points of each reaction have been calculated to determine the thermodynamics of the reactions investigated. A substantial decrease in reaction enthalpies and Gibbs energies was found for glycine–ammonia and glycine–glycine reactions coordinated by Mg²⁺, Cu²⁺, and Zn²⁺ ions compared to those of the uncoordinated 2-aminoacetamide bond formation. The formation of a dipeptide is a more exothermic process than the creation of simple 2-aminoacetamide from glycine. The energetic effect of the transition metal ions Cu²⁺ and Zn²⁺ is of similar strength and more pronounced than that of the Mg²⁺ cation. The basicity order of the amides investigated shows the order: NH₂CH₂CO₂H < NH₂CH₂CONH₂ < NH₂CH₂CONHCH₂CO₂H. Interaction enthalpies and Gibbs energies of metal ion–amide complexes increase as Mg²⁺2+2+. In both reactant (glycine) and reaction products (2-aminoacetamide, N-glycylglycine) dihydration caused considerable reduction (about 200–500 kJ-mol^–1) of the strength of the bifurcated metal–amide bonds. Solvent effects also reduce the reaction enthalpy and Gibbs energy of reactions under study.     

钙钛矿结构荧光材料MZrO3:Eu3+,A (M=Ca2+, Ba2+; A=Li+, Na+, K+)的制备及其发光性质

Calcium and barium zirconate powders based upon CaZrO₃:Eu³⁺,A and BaZrO₃:Eu³⁺,A (A=Li⁺, Na⁺, K⁺) were prepared by combustion synthesis method and heating to ~1000℃ to improve crystallinity.The structure and morphology of materials were examined by X-ray diffraction (XRD) and scanningelectron microscopy (SEM). XRD results showed that CaZrO₃:Eu³⁺,A and BaZrO₃:Eu³⁺,A (A=Li⁺, Na⁺, K⁺) perovskites possessed orthorhombic and cubic structures, respectively. The morphologies of all powderswere very similar consisting of small, coagulated, cubical particles with narrow size distributions andsmooth and regular surfaces. The characteristic luminescences of Eu³⁺ ions in CaZrO₃:Eu³⁺,A (A=Li⁺, Na⁺, K⁺) lattices were present with strong emissions at 614 and 625 nm for ⁵D₀→⁷F₂ transitions with other weakeremissions observed at 575, 592, 655, and 701 nm corresponding to ⁵D₀→⁷F_n transitions (where n=0, 1, 3, 4 respectively). In BaZrO₃:Eu³⁺ both the ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transitions at 595 and 613 nm were strong.Photoluminescence intensities of CaZrO₃:Eu³⁺ samples were higher than those of BaZrO₃:Eu³⁺ lattices. Thisremarkable increase of photoluminescence intensity (corresponding to ⁵D₀→⁷F_n transitions) was observedin CaZrO₃:Eu³⁺ and BaZrO₃:Eu³⁺ if co-doped with Li⁺ ions. An additional broad band composed of manypeaks between 440 to 575 nm was observed in BaZrO₃:Eu³⁺,,A samples. The intensity of this band wasgreatest in Li⁺ co-doped samples and lowest for K⁺ doped samples.     

Study on the synthesis of novel fluorescent macrocyclic sensors and their sensitive properties for Cu2+ and Fe3+ in aqueous solution

In this work, we synthesised and characterised three novel fluorescence macrocyclic sensors containing optically active dansyl groups. The studies for the interaction of the synthesised compounds with various mental ions (Li⁺, Na⁺, K⁺, Ag⁺, Mg²⁺, Ca²⁺, Ba²⁺, Pb²⁺, Zn²⁺, Co²⁺, Cd²⁺, Hg²⁺, Ni²⁺, Cu²⁺, Mn²⁺, Cr³⁺, Al³⁺, Fe³⁺) were performed by fluorescence titration, Job’s plot, ESI-MS and DFT calculations. The results showed that the sensors 1a–1c displayed selective recognition for Cu²⁺ and Fe³⁺ ions and formed stoichiometry 1:1 complex through PET mechanism in DMSO/H₂O solution (1:1, v/v, pH 7.4 of HEPES). The binding constant (K) and detection limit were calculated.     

Electronic state of Fe used as Mössbauer probe in the perovskites LaMO3 (M=Ni and Cu)

For the first time a comparative study of rhombohedral LaNiO₃ and LaCuO₃ oxides, using ⁵⁷Fe Mössbauer probe spectroscopy (1% atomic rate), has been carried out. In spite of the fact that both oxides are characterized by similar crystal structure and metallic properties, the behavior of ⁵⁷Fe probe atoms in such lattices appears essentially different. In the case of LaNi_0.99Fe_0.01O₃, the observed isomer shift (δ) value corresponds to Fe³⁺ (3d⁵) cations in high-spin state located in an oxygen octahedral surrounding. In contrast, for the LaCu_0.99Fe_0.01O₃, the obtained δ value is comparable to that characterizing the formally tetravalent high-spin Fe⁴⁺(3d⁴) cations in octahedral coordination within Fe(IV) perovskite-like ferrates. To explain such a difference, an approach based on the qualitative energy diagrams analysis and the calculations within the cluster configuration interaction method have been developed. It was shown that in the case of LaNi_0.99Fe_0.01O₃, electronic state of nickel is dominated by the d⁷ configuration corresponding to the formal ionic “Ni³⁺-O²⁻” state. On the other hand, in the case of LaCu_0.99Fe_0.01O₃ a large amount of charge is transferred via Cu-O bonds from the O:2p bands to the Cu:3d orbitals and the ground state is dominated by the d⁹L configuration (“Cu²⁺−O” state). The dominant d⁹L ground state for the (CuO₆) sublattice induces in the environment of the ⁵⁷Fe probe cations a charge transfer Fe³⁺+O⁻(L)→Fe⁴⁺+O²⁻, which transforms “Fe³⁺” into “Fe⁴⁺” state. The analysis of the isomer shift value for the formally “Fe⁴⁺” ions in perovskite-like oxides clearly proved a drastic influence of the 4s iron orbitals population on the Fe−O bonds character.     

Stability studies on 1:1 or 1:3 stoichiometry complexes of hexaza tripods with zinc(II), copper(II), nickel(II) and cobalt(II)

The coordination properties of two C₃-symmetry hexaza tripods, 1,3,5-tri(2,5-diazahexyl)benzene (L1) and 1,3,5-tri(2,5-diazaheptyl)benzene (L2), towards Zn²⁺, Cu²⁺, Ni²⁺ and Co²⁺ ions, studied by potentiometric techniques, are reported. Both ligands form quite stable complexes either in a 1:1 or 1:3 M:L stoichiometry, presenting a preferential coordination order: Zn²⁺ < Cu²⁺ > Ni²⁺ > Co²⁺. It is observed that the different configurations of metal complexes are achieved due to the fact that tripodal ligands are flexible and not constrained into a rigid geometry.     

Spectroscopic Characterization of <Emphasis Type="Italic">N,N-bis</Emphasis>(2-{[(2,2-Dimethyl-1,3-Dioxolan-4-yl)Methyl]Amino}Ethyl) N′,N′-Dihydroxyethanediimidamide and Its Complexes

A new dioxime ligand, N,N-bis(2-{[(2,2-dimethyl-1,3-dioxolan-4-yl)methyl]amino} ethyl)N′,N′-dihydroxyethanediimidamide (H₂L), and its mononuclear complexes with Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺ and Cd²⁺ are synthesized. H₂L forms transition metal complexes [Co(LH)₂(H₂O)₂] and [M(LH)₂] (M = Ni²⁺, Cu²⁺) with a metal : ligand ratio of 1 : 2. Complexes [M(H₂L)(Cl)₂] (Zn²⁺, Cd²⁺) have a metal : ligand ratio of 1 : 1. The mononuclear Co²⁺, Ni²⁺, and Cu²⁺ complexes indicate that the metal ions coordinate ligand through its two N atoms, as the most of dioximes. In the Co²⁺ complex, two water molecules and in the Zn²⁺ and Cd²⁺ complexes two chloride ions are also coordinated to the metal ion. The structures of these compounds are identified by elemental analyses, IR, ¹H and ¹³C NMR, electronic spectra, magnetic susceptibility measurements, conductivity, and thermogravimetric analysis.__________From Koordinatsionnaya Khimiya, Vol. 31, No. 7, 2005, pp. 540–544.Original English Text Copyright © 2005 by Canpolat, Kaya.The text was submitted by the authors in English.     

Ternary [Al2O3–electrolyte–Cu] species: EPR spectroscopy and surface complexation modeling

Cu²⁺ binding on γ-Al₂O₃ is modulated by common electrolyte ions such as Mg²⁺, , and in a complex manner: (a) At high concentrations of electrolyte ions, Cu²⁺ uptake by γ-Al₂O₃ is inhibited. This is partially due to bulk ionic strength effects and, mostly, due to direct competition between Mg²⁺ and Cu²⁺ ions for the SO⁻ surface sites of γ-Al₂O₃. (b) At low concentrations of electrolyte ions, Cu²⁺ uptake by γ-Al₂O₃ can be enhanced. This is due to synergistic coadsorption of Cu²⁺ and electrolyte anions, and _. This results in the formation of ternary surface species (SOH₂SO₄Cu)⁺, (SOH₂PO₄Cu), and (SOH₂HPO₄Cu)⁺ which enhance Cu²⁺ uptake at pH < 6. The effect of phosphate ions may be particularly strong resulting in a 100% Cu uptake by the oxide surface. (c) EPR spectroscopy shows that at pH  pH_PZC, Cu²⁺ coordinates to one SO⁻ group. Phosphate anions form stronger, binary or ternary, surface species than sulfate anions. At pH  pH_PZC Cu²⁺ may coordinate to two SO⁻ groups. At pH  pH_PZC electrolyte ions and are bridging one O-atom from the γ-Al₂O₃ surface and one Cu²⁺ ion forming ternary [γ-Al₂O₃/elecrolyte/Cu²⁺] species.     

Graphene quantum dots with Zn2+ and Ni2+ conjugates can cleave supercoiled DNA

Graphene quantum dots (GQDs), inheriting the superb property of graphene oxide, possess smaller lateral size and high biocompatibility, thus having potential in biomedical applications. We previously discovered that GQDs, combining with Cu²⁺ ions, could cleave DNA primarily through an oxidative pathway; yet, oxidative DNA cleavage is not practically preferred in biology. In this work, we explore the DNA cleavage ability of GQDs with Zn²⁺ and Ni²⁺. Zn²⁺ and Ni²⁺ alone are incapable of cleaving supercoiled DNA, but when combining with the GQDs, Zn²⁺ and Ni²⁺ exhibit DNA cleavage activity. However, the activity of these two systems is much lower than that of GQDs/Cu²⁺, and GQDs/Ni²⁺ is less active than GQDs/Zn²⁺. The functional mechanism of GQDs/Ni²⁺ and GQDs/Zn²⁺ is different from that of GQDs/Cu²⁺. The GQDs play a key role in the two systems; the redox inactive Zn²⁺ and Ni²⁺ ions assist to generate the oxidative species that eventually lead to the DNA cleavage. The current results together with our previous result indicate that GQDs together with metal ions can cleave supercoiled DNA, and their cleavage activities depend on the properties of metal ions: for redox active metal ions, metal ions play key roles, for redox inactive metal ions, GQDs are dominant.     

Theoretical study on reactions of cyclic-N3 with NO, NO2 and Cl2

In this article, we report our detailed mechanistic study on the reactions of cyclic-N₃ with NO, NO₂ at the G3B3//B3LYP/6-311+G(d) and CCSD(T)/aug-cc-pVTZ//QCISD/6-311+G(d)+ZPVE levels; the reactions of cyclic-N₃ with Cl₂ was studied at the G3B3//B3LYP/6-311+G(d) and CCSD(T)/aug-cc-pVTZ//QCISD/6-31+G(d)+ZPVE levels. Both of the singlet and triplet potential-energy surfaces (PESs) of cyclic-N₃ + NO, cyclic-N₃ + NO₂ and the PES of cyclic-N₃ + Cl₂ have been depicted. The results indicate that on singlet PESs cyclic-N₃ can undergo the barrierless addition–elimination mechanism with NO and NO₂ forming the respective dominant products N₂ + ¹cyclic-NON and ¹NNO(O) + N₂. Yet the two reactions on triplet PESs are much less likely to take place under room temperature due to the high barriers. For the cyclic-N₃ + Cl₂ reaction, a Cl-abstraction mechanism was revealed that results in the product cyclic-N₃Cl + Cl with an overall barrier as high as 14.7 kcal/mol at CCSD(T)/aug-cc-pVTZ//QCISD/6-31+G(d)+ZPVE level. So the cyclic-N₃ radical could be stable against Cl₂ at low temperatures in gas phase. The present results can be useful for future experimental investigation on the title reactions.     

Electronic structure of X2 Y3 molecules (X = B, Al, Ga; Y = O,S): A theoretical study

Ab initio molecular orbital and density functional theory calculations on X₂Y₃ (X = B, Al,Ga; Y = O,S) indicate a bent structure withC _2v symmetry to be the preferred arrangement for B₂ O₃, B₂ S₃ and Al₂S₃. In contrast, the linear isomer is favoured for Al₂ O₃ and Ga₂ O₃. These are in agreement with the experimentally observed structures. The electronegativity difference between X and Y, the MO patterns and the ionic nature of the bonding explain variations in the molecular structure. The results from the two theoretical approaches (MP2/6-31G* and Becke3LYP/6-311 +G* level) are comparable.     

Synthesis, crystal structure, infrared and Raman spectra of Sr4Cu3(AsO4)2(AsO3OH)4·3H2O and Ba2Cu4(AsO4)2(AsO3OH)3

The two new compounds, Sr₄Cu₃(AsO₄)₂(AsO₃OH)₄·3H₂O (1) and Ba₂Cu₄(AsO₄)₂(AsO₃OH)₃(2), were synthesized under hydrothermal conditions. They represent previously unknown structure types and are the first compounds synthesized in the systems SrO/BaO-CuO-As₂O₅-H₂O. Their crystal structures were determined by single-crystal X-ray diffraction [space group C2/c, a=18.536(4) Å, b=5.179(1) Å, c=24.898(5) Å, β=93.67(3)°, V=2344.0(8) Å³, Z=4 for 1; space group P4₂/n, a=7.775(1) Å, c=13.698(3) Å, V=828.1(2) Å³, Z=2 for 2]. The crystal structure of 1 is related to a group of compounds formed by Cu²⁺-(XO₄)³⁻ layers (X=P⁵⁺, As⁵⁺) linked by M cations (M=alkali, alkaline earth, Pb²⁺, or Ag⁺) and partly by hydrogen bonds. In 1, worth mentioning is the very short hydrogen bond length, D···A=2.477(3) Å. It is one of the examples of extremely short hydrogen bonds, where the donor and acceptor are crystallographically different. Compound 2 represents a layered structure consisting of Cu₂O₈ centrosymmetric dimers crosslinked by As1φ₄ tetrahedra, where φ is O or OH, which are interconnected by Ba, As2 and hydrogen bonds to form a three-dimensional network. The layers are formed by Cu₂O₈ centrosymmetric dimers of CuO₅ edge-sharing polyhedra, crosslinked by As1O₄ tetrahedra. Vibrational spectra (FTIR and Raman) of both compounds are described. The spectroscopic manifestation of the very short hydrogen bond in 1, and ABC-like spectra in 2 were discussed.     

Determination of sulfur contents of SO3, S2O3 and S based on the electrocatalytic interaction with homogeneous mediator tris(2,2'-bipyridyl)Ru(II)

A sensitive voltammetric method has been developed for the determination of total or single species of sulfur anions containing sulfide, sulfite and thiosulfate. The method is based on the catalytic effect of tris(2,2'-bipyridyl)Ruthenium(II) (Ru(bpy)₂^+ 2) as a homogeneous mediator on the oxidation of those anions at the surface of a glassy carbon electrode. A reversible redox couple of Ru(II)/Ru(III) were observed as a solute in aqueous solution. Cyclic voltammetry study showed that the catalytic current of the system depends on the concentration of the anions. Optimum pH values for voltammetric determination of sulfite, thiosulfate and sulfide has been found to be 5.6, 10.0 and 10.0, respectively. Under the optimized conditions the calibration curves have been obtained linear in the concentration ranges of 0.8–500.0, 0.4–1000.0 and 0.5–5000.0 µmol L^− 1 of SO₃²⁻, S₂O₃²⁻ and S²⁻, respectively. The detection limits have been calculated to be 0.40, 0.17 and 0.33 µmol L^− 1 for SO₃²⁻, S₂O₃²⁻ and S²⁻, respectively. The diffusion coefficients of sulfite and thiosulfate have been estimated using chronoamperometry. The chronoamperometric method also has been used to determine the catalytic rate constant for catalytic reaction of the Ru(bpy)₂^+ 2 with sulfite and thiosulfate. Finally the proposed method has been used for the determination of total sulfur contents in real samples of water and wastewater. Moreover the sulfite content in sugar and sulfur dioxide in air has been determined with satisfactory results.     

A Conductometric Study of Complexation Reactions Between Dibenzo-18-Crown-6 (DB18C6) with Cu2+, Zn2+, Tl+ and Cd2+ Metal Cations in Dimethylsulfoxide–Ethylacetate Binary Mixtures

The complex formation between Cu²⁺, Zn²⁺, Tl⁺ and Cd²⁺ metal cations with macrocyclic ligand, dibenzo- 18-crown-6 (DB18C6) was studied in dimethylsulfoxide (DMSO)–ethylacetate (EtOAc) binary systems at different temperatures using conductometric method. In all cases, DB18C6 forms 1:1 complexes with these metal cations. The stability constants of the complexes were obtained from fitting of molar conductivity curves using a computer program, Genplot. The non-linear behaviour which was observed for variations of log K _f of the complexes versus the composition of the mixed solvent was discussed in terms of changing the chemical and physical properties of the constituent solvents when they mix with one another and, therefore, changing the solvation capacities of the metal cations, crown ether molecules and even the resulting complexes with changing the mixed solvent composition. The results show that the selectivity order of DB18C6 for the metal cations in pure ethylacetate and pure dimethylsulfoxide is: Tl⁺ > Cu²⁺ > Zn²⁺ > Cd²⁺ but the selectivity order is changed with the composition of the mixed solvents. The values of enthalpy changes (ΔH°_C) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in standard enthalpy (ΔS°_C) were calculated from the relationship: ΔG°_C,298.15=ΔH°_C − 298.15 ΔS°_C. The obtained results show that in most cases, the complexes are enthalpy stabilized, but entropy destabilized and the values of ΔH°_C and ΔS°_C depend strongly on the nature of the medium.     

Photoluminescence properties of La(PO3)3:Tb under VUV excitation

La_1−x(PO₃)₃:Tb_x³⁺ (0<x0.6) were prepared using solid-state reaction. The vacuum ultraviolet (VUV) excitation spectrum of La_0.55(PO₃)₃:Tb_0.45³⁺ indicates that the absorption of (PO₃)₃³⁻ groups locates at about 163 and 174 nm and the absorption bands of (PO₃)₃³⁻ groups (174 nm) and La³⁺–O²⁻ (200 nm) and Tb³⁺ (213 nm) overlap each other. These results imply that the (PO₃)₃³⁻ groups can efficiently absorb the excited energy around 172 nm and transfer the energy to Tb³⁺. Under 172 nm excitation, the optimal photoluminescence (PL) intensity is obtained when Tb concentration reaches 0.45 and is about 71% of commercial phosphor Zn_1.96SiO₄:0.04 Mn²⁺ with chromaticity coordinates of (0.343, 0.578) and the decay time of about 4.47 ms.     

IR and Raman spectra of two layered aluminium phosphates Co(en)3Al3P4O16 · 3H2O and [NH4]3[Co(NH3)6]3[Al2(PO4)4]2 · 2H2O

The FT IR and FT Raman spectra of Co(en)₃Al₃P₄O₁₆ · 3H₂O (compound I) and [NH₄]₃[Co(NH₃)₆]₃[Al₂(PO₄)₄]₂ · 2H₂O (compound II) are recorded and analysed based on the vibrations of Co(en)₃³⁺, Co(NH₃)₆³⁺, NH₄⁺, Al---O---P, PO₃, PO₂ and H₂O. The observed splitting of bands indicate that the site symmetry and correlation field effects are appreciable in both the compounds. In compound I, the overtone of CH₂ deformation Fermi resonates with its symmetric stretching vibration. The NH₄ ion in compound II is not free to rotate in the crystalline lattice. Hydrogen bonding of different groups is also discussed.