Relativistic calculations of AuSi+ and AuSi−

Theoretical calculations of the electronic structure of the ground state and a series of excited states of the AuSi⁺ and AuSi⁻ molecules are presented. The calculations were carried out with the spin-free relativistic infinite-order two-component (IOTC) method and high-level complete active space self-consistent field/complete active space perturbation theory correlated methods. The spin-orbit (SO) coupling was introduced via the restricted active space state interaction method with the use of the atomic mean-field SO integrals. The work presents the spectroscopic parameters of calculated states and full potential energy curves of the ionic AuSi⁺ and AuSi⁻ structures for the first time. Electrostatic potential maps projected on the electron density surface illustrate the significant relativistic effects on going from nonrelativistic to scalar relativistic treatments.     

Does Thermochemical Mimicry Extend to Gibbs Energies? The Differences of K+ and NH4 +, and of Na+ and H3O+

Structural Chemistry -     

Bioadsorption and ion exchange of Cr3+ and Pb2+ solutions with algae

Heavy metals can be removed from effluents and recovered using physico-chemical mechanisms as biosorption processes. In this work “Arribada” seaweed biomass was employed to assess its biosorptive capacity for the chromium (Cr³⁺) and lead (Pb²⁺) cations that usually are present in waste waters of plating industries. Equilibrium and kinetic experiments were conducted in a mixed reactor on a batch basis. Biosorption equilibrium and fluid-solid mass transfer constants data were analyzed through the concept of ion exchange sorption isotherm. The respective equilibrium exchange constants (K _eqCr=173.42, K _eqPb=58.86) and volumetric mass transfer coefficients ((k _mCr a)′=1.13×10⁻³ s⁻¹, (k _mPb a)′=0.89×10⁻³ s⁻¹) were employed for the dynamic analysis of Cr and Pb sorption in a fixed-bed flow-through sorption column. The breakthrough curves obtained for both metals were compared with the predicted values by the heterogeneous model (K _eqCr=171.29, K _eqPb=60.14; k _mCr a=7.81×10⁻² s⁻¹, k _mPb a=2.43×10⁻² s⁻¹), taking into account the mass transfer process. The results suggest that these algae may be employed in a metal removal/recovery process at low cost. An erratum to this article can be found at     

Reactions of Au+ and Au− with benzene and fluorine-substituted benzenes

Reactions of gold anions and cations generated by laser desorption/ionization were studied in the FTICR spectrometer. Au⁻ associated with C₆F₆ to give the novel Au⁻(C₆F₆) complex, whose binding energy was estimated to be 24 ± 4 kcal mol⁻¹ from analysis of the radiative association (RA) kinetics. Au⁺ associated with C₆F₅H to give Au⁺(C₆F₅H), with binding energy estimated to be 31 kcal mol⁻¹. Au⁺ reacted with C₆H₆ to form the well known Au⁺(C₆H₆) and Au⁺(C₆H₆)₂ complexes. The observation of rapid charge transfer from Au⁺(C₆H₆) to C₆H₆ was interpreted as showing that benzene binds more strongly to neutral Au than to Au⁺. The neutral Au–C₆H₆ bond is accordingly concluded to be stronger than about 70 kcal mol⁻¹.     

Dynamics and mode-selected reaction of NCO+H_2→HNCO+H

The reaction path of the reaction NCO+H2→HNCO + H has been traced by Fukui's theory and the ab initio method. On this basis, the dynamical properties along the reaction path, canonical variational theory (CVT) rate constants and vibrational-mode-selected rate constants have been computed. The results show that the effect of the electron correlation energy on the activation barrier is large, and tiros the correction by MP4 method is effective; the results also show that the recrossing and tunneling effects exist, and thus the corrections by the variational transition state theory (VTST) and the small curvature (SC) approximation method are also effective. In the reaction, the coupling and energy transfer between mode 8(7) and reaction path are strong, so the rate is effectively enhanced while these modes, especially H2 stretching, are vibrationally excited.     

Mixed Ligand Complexes of Am3+, Cm3+ and Eu3+ with HEDTA and HEDTA + NTA—Complexation Thermodynamics and Structural Aspects

The stability constants and the associated thermodynamic parameters of formation for the 1:1 binary complexes of Am³⁺, Cm³⁺ and Eu³⁺ with N-(2-hydroxyethyl) ethylenediaminetriacetate (HEDTA) and their 1:1:1 ternary complexes with HEDTA + NTA (nitrilotriacate) were determined by distribution ratio measurements using solvent extraction in aqueous solutions of I=0.10?mol?L^?1 (NaClO₄) at temperatures of 0?C45?°C. Formation of these complexes is favored by both the enthalpy (exothermic) and the entropy (endothermic) terms. Luminescence lifetime measurements with Cm and Eu were used to study the coordination environment of these complexes over a range of concentrations and pH values. In the binary complexes M(HEDTA), HEDTA is a hexadentate ligand with three waters of hydration, while in the ternary complexes M(HEDTA)(NTA)^3? we propose that the HEDTA retaines hexadentate coordination with NTA binding via three sites, depending on the pH of the solution, with the observation that the complex may contain a single water of hydration.     

Determination of the Rate Constants of the Reactions Cr + O2 + M → CrO2 + M and Cr + O2 → CrO + O

Kinetics and Catalysis - The rate constants of the interactions of chromium atoms with molecular oxygen through recombination Cr + O2 + M → CrO2 + M (I) and exchange Cr + O2 → CrO + O...     

Rotational analysis and deperturbation of the A2Π → X2Σ+ and B'2Σ+ → X2Σ+ emission spectra of MgH

Deperturbation analysis of the A(2)Π → X(2)Σ(+) and B(')(2)Σ(+) → X(2)Σ(+) emission spectra of (24)MgH is reported. Spectroscopic data for the v = 0 to 3 levels of the A (2)Π state and the v = 0 to 4 levels of the B'(2)Σ(+) state were fitted together using a single Hamiltonian matrix that includes (2)Π and (2)Σ(+) matrix elements, as well as off-diagonal elements coupling several vibrational levels of the two states. A Dunham-type fit was performed and the resulting Y(l,0) and Y(l,1) coefficients were used to generate Rydberg-Klein-Rees (RKR) potential curves for the A (2)Π and the B'(2)Σ(+) states. Vibrational overlap integrals were computed from the RKR potentials, and the off-diagonal matrix elements coupling the electronic wavefunctions (a(+) and b) were determined. Zero point dissociation energies (D(0)) of the A(2)Π and B'(2)Σ(+) states of (24)MgH were determined to be 12,957.5 ± 0.5 and 10,133.6 ± 0.5 cm(-1), respectively. Using the Y(0,1) coefficients, the equilibrium internuclear distances (r(e)) of the A(2)Π and B'(2)Σ(+) states were determined to be 1.67827(1) ? and 2.59404(4) A?, respectively.     

Transport of 125I−, 137Cs+ and 85Sr2+ in granitoidic rock and soil columns

Transport of ¹²⁵I^?, ¹³⁷Cs⁺ and ⁸⁵Sr²⁺ radionuclides in crushed granitoidic rocks and homogenized soils was studied. Two simple methods for calculation of breakthrough curves in flow column experiments with groundwater as transport medium have been described. The first method, so called non-linear approach, is derived on the assumption of a reversible non-linear sorption isotherm described with Freundlich equation, i.e., with non-constant distribution and retardation coefficients. The second method, so-called linear approach, is applied for reference only, and is based on the assumption of a reversible sorption characterized with linear sorption isotherm, i.e., with constant distribution and retardation coefficients. Both methods model the experimental breakthrough curves with the integrated form of the simple 1-D advection–dispersion equation (ADE) expressed analytically for pulse application of radiotracer to the liquid phase before entering the columns. The integrated form of the ADE equation was modified by the so-called peak position and peak height correction coefficients the advantage of which consists among others in the elimination of the influence of starting concentration. The comparison of both approaches has shown that fitting by means of non-linear approach has given rather reliable values of the transport parameters and calculated dependences, especially in a case of ¹³⁷Cs system characterized evidently with non-linear type of sorption isotherms. As for ¹²⁵I^?, the sorption capacity of all solid samples studied is nearly on the zero level and ¹²⁵I^? is practically not retarded, and from this point of view it behaves as non-interacting component. In addition, it was found that the modified ADE gives rather better results than the classical one.     

Photoacoustic Spectrometry Investigation and Determination of Rare Earth Ions Ho3+ and Nd3+ in a Solution

A home-made high sensitive photoacoustic transducer was used to determine the photoacoustic signal in a solution. The photoacoustic spectra of Ho in different solvents were measured and comparedwith its absorption spectrum. The affection factors of photoacousticsensitivity are discussed. The trivalent rare earth ions Ho3+ and Nd3+in an aqueous acetonitrile solution were determined. The detection limit is 5×10-8 mol/L for Ho3+ and 1.0 ×10-7 mol/L for Nd3+, and corresponds to the absorbance of 1.5×10 and 6.3×10-7.respectively.     

Synthesis of β- and γ-carbolines via ruthenium and rhodium catalysed [2+2+2] cycloadditions of yne-ynamides with methylcyanoformate

A flexible approach towards substituted β- and γ-carbolines based on transition metal catalysed [2+2+2] cycloaddition reactions between functionalised yne-ynamides and methylcyanoformate is described. The versatility of this new reaction sequence is demonstrated by its application in the total synthesis of the marine natural product eudistomin U.     

Kinetics and thermochemistry of [2π + 2σ + 2σ]-cycloaddition of quadricyclane to tetracyanoethylene

Kinetic data for the unusual [2π + 2σ + 2σ]-cycloaddition of quadricyclane to tetracyanoethylene in toluene have been obtained for the first time. The same reaction in 1,4-dioxane appears to be the most exothermic among known cycloaddition reactions. The entropy of activation and reaction volume differ only slightly from the corresponding parameters of conventional Diels–Alder reactions.     

Adsorption and diffusion of propane and propylene in Ag+-impregnated MCM-41

Equilibrium data and diffusion characteristics of propane and propylene were determined on mesoporous adsorbents modified with an organic molecule (APTES) and/or impregnated with AgNO₃, in order to obtain a separation by adsorption via π-complexation. Adsorption capacities were determined by a gravimetric technique, while diffusion characteristics were evaluated by the ZLC technique. The equilibrium isotherms data showed that the modification with an organic molecule will weaken the π-interaction between Ag⁺ and double C=C bond. On the other hand slightly higher adsorption capacities for propylene (about 1.5 mol/kg) were obtained for the sample prepared by a direct impregnation with larger amounts of AgNO₃ (M4 sample). Diffusion runs confirmed that the propane desorption rate on M4 sample was much higher compared to propylene. This evidence leads to a potential application of that adsorbent material for a kinetic separation.     

Synthesis and phosphorescence properties of Dy3+ and (Pr3+–Dy3+) in MgTiO3

Using tetra-n-butyl titanate and magnesium nitrate as raw materials, Dy³⁺ and Pr³⁺ ions in the matrix of magnesium titanate (MgTiO₃) was successfully synthesized by a modified solid-state reaction. The mixtures to achieve a solid-state reaction were heated in porcelain crucibles at 600?°C for 2?h, 900?°C for 6?h, and 1000.0?°C for 2?h. The reaction products obtained in an air atmosphere were characterized by X-ray powder diffractions. The optimization of reaction conditions were carried out by thermal gravimetry and differential thermal analysis methods. Surface and elemental analyses were performed by using on SEM instrument. The excitation and emission spectra were recorded by photoluminescence spectrophotometer.     

Structure and potential energy surface of K+·CX2

The potential energy surface of K⁺·CO₂ and K⁺·CS₂ complexes are determined at high levels of ab initio theory (CCSD), B3LYP, and MP2 using different basis sets. These calculations predict the existence of three minima for K⁺·CO₂ complex; linear, quadrilateral and Y-shape, and two minima for K⁺·CS₂ complex; bent and Y-shape. In addition, the binding energies, and other thermodynamic quantities are calculated at different levels of theories. Our calculations show that the difference in the global minima geometries of both complexes is mainly due to the sign of the quadrupole moment of CO₂ and CS₂ molecules.     

Significant enhancement of luminescence intensity of CaTiO3:Eu3+ red phosphor prepared by sol–gel method and co-doped with Bi3+ and Mg2+

In this study, red phosphors Ca_1?n Mg _n TiO₃:Eu³⁺,Bi³⁺ were prepared by the sol?Cgel method and the impact of single dopant, co-dopants and solid solutions on the photoluminescence of the samples has been also investigated. Our results show that the crystal structure of the host does not have distinct changes when doped with Eu³⁺, Bi³⁺ and/or Mg²⁺. The emission intensity at 615?nm of Eu³⁺ increased at the presence of Bi³⁺ ions owing to the energy transfer from Bi³⁺ ion to Eu³⁺ ion. Moreover, with the addition of Mg²⁺, the red emission of the phosphor was further enhanced due to the stronger absorption at 399 and 467?nm, which match well with the emission of near-UV (395?C400?nm) and blue-LED (450?C470?nm), respectively. Under the near-UV (399?nm) or blue light (467?nm) excitation, the fluorescence quantum yield of the optimal composition Ca_0.9Mg_0.1TiO₃:0.18Eu³⁺,0.018Bi³⁺ is 0.36 and 0.41, respectively, which possesses the higher photoluminescence intensity than CaMoO₄:0.2Bi³⁺,0.05Eu³⁺ and the commercially available Y₂O₂S:Eu³⁺ phosphors under near-UV excitation. Based on these results, we are currently considering the potential application of Ca_0.9Mg_0.1TiO₃:Eu³⁺,Bi³⁺ as a near-UV or blue-chip convertible red-emitting phosphor.     

Batch and continuous fixed-bed column adsorption of Cs+ and Sr2+ onto montmorillonite–iron oxide composite: Comparative and competitive study

A montmorillonite–iron oxide composite (MIOC) was prepared to assess its effectiveness in the removal of Cs⁺ and Sr²⁺ from aqueous solution. A comparative and competitive adsorption study was conducted in single and binary systems. Used materials have been characterized by X-ray diffraction (XRD) and Infrared spectroscopy. Adsorption of Cs⁺ and Sr²⁺ as a function of contact time and pH was investigated, adsorption data of single metal solutions were well fitted to the Freundlich–Langmuir isotherm models. Equilibrium isotherms for the binary removal of Cs⁺ and Sr²⁺ by MIOC have been analyzed by using non modified and extended Langmuir models with a satisfactory R ² values. Neutral solution pH was found to be favorable for both single and binary systems. The adsorption model analysis revealed that MIOC was more selective for Sr than Cs. The maximum adsorption capacities for individual Cs⁺ and Sr²⁺ solutions were 52.6 and 55.5 mg g^?1, respectively. While the maximum uptakes in the binary system were 41.6 and 47.6 mg g^?1 for Cs⁺ and Sr²⁺, respectively. Column adsorption experiments were carried out at room temperature under the effect of various operating parameters such as bed depth, initial cation concentration and flow rate, Breakthrough curves were well fitted to the Thomas model. Desorption experiments were also conducted to assess the possibility for the reuse of adsorbent and the recovery of cations.     

Structures and stability of N9, N9 − and N9 + clusters

 Ab initio molecular orbital calculations for N₉, N⁻ ₉ and N⁺ ₉ isomers were carried out at the HF/ 6-31G*, B3PW91/6-31G*, B3LYP/6-31G* and MP2/ 6-31G* levels of theory. Stable equilibrium geometric structures were determined by harmonic vibrational frequency analyses at the HF/6-31G*, B3PW91/6-31G* and B3LYP/6-31G* levels of theory. The most stable free-radical N₉ cluster is structure 1 with C _{2 v} symmetry and that of anion N⁻ ₉ is structure 3 with C _s symmetry. Only one stable structure of the N⁺ ₉ cation with C _{2 v} symmetry was predicted. Their potential application as high-energy-density materials has been examined. Received: 15 June 1999 / Accepted: 11 October 1999 / Published online: 14 March 2000     

Heat capacities and volumes of methanol+acetonitrile mixtures at 5 and 25°C

Densities and heat capacities of methanol + acetonitrile mixtures were determined over the whole composition range at 5 and 25°C. Apparent and partial molar volumes and heat capacities for both components of the mixture were calculated from these data. These functions for acetonitrile run monotonously over the whole composition range of the mixture at both temperatures, while those for methanol exhibit extrema (volumes-minimum and heat capacities-maximum) at high acetonitrile content. The reasons of the observed behavior of the system are discussed.     

Tl-speciation of aqueous samples – a review of methods and application of IC-ICP-MS/LC-MS procedures for the detection of (CH3)2Tl+ and Tl+ in river water

This study provides an overview on Tl-speciation methods developed in the last years. Most of them require transformation of a species and do not allow direct detection of the species of interest. LC-MS and IC-ICP-MS methods are optimised for direct analysis of the Tl-species Tl⁺ and (CH₃)₂Tl⁺ (dimethylthallium (DMT)) in freshwater on a ng L^?1 level. The methods are applied in a study of water from Vicht River in Stolberg (Germany). Tl⁺ is shown to be at least in part derived from anthropogenic sources among which the industrial sources may be significant. The natural occurrence of DMT is proven, although this Tl-species is temporally variable in abundance and Tl⁺ predominates.