Discussion on complexation reactions between dicyclohexyl-18-crown-6 (DCH18C6) with Na+, K+, Cs+, Rb+, and Tl+ metal cations in acetonitrile-water binary mixtures

The complex formation between Na⁺, K⁺, Cs⁺, Rb⁺ and Tl⁺ metal cations with macrocyclic ligand, dicyclohexyl-18-crown-6 (DCH18C6) was studied in acetonitrile-water (AN-H₂O) binary systems at different temperatures using conductometric method. DCH18C6 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 results show that the selectivity order of DCH18C6 for the metal cations in acetonitrile-water mixtures (AN = 25.3 and 50.4 mol %) is: Tl⁺ > K⁺ > Rb⁺ > Cs⁺ > Na⁺. A non-linear behaviour was observed between the log K _f of the complexes versus the composition of the mixed solvent which it related to changes of acidity, basicity, polarity and also polarizability of AN-H₂O mixtures with the composition of this binary solution. The values of standard enthalpy changes (ΔH _s⁰) for complexation reactions were obtained from the slope of the van’t Hoff plots and the changes in the standard entropy (ΔS _s⁰) were calculated from the relationship: ΔG _s,298.15⁰ = ΔH _s⁰ − 298.15ΔS _s⁰. The obtained results show that in most cases, the complexes are enthalpy stabilized but entropy destabilized. Original Russian Text ? M.H. Soorgi, G.H. Rounaghi, M.S. Kazemi, 2008, published in Zhurnal Obshchei Khimii, 2008, vol. 78, No. 10, pp. 1627–1632.     

Molecular-beam-laser studies of the states X1Σ+ and A0+ of PbS

By using a molecular-beam apparatus, laser excitation spectra and microwave-optical double-resonance spectra were observed on the electronic states X¹Σ⁺ and A0⁺ of PbS. For the microwave spectra a resolution up to 10 kHz was achieved and microwave two-photon transitions could be detected. All information was combined into single fitting routine including data from other sources. Besides the usual Dunham parameters the fit model takes account of the breakdown of the Born-Oppenheimer approximation and the isotopic field shift. From the field shift of the electronic energy, the vibrational motion and the rotational motion the electron density as a function of the internuclear distance at the Pb nucleus is derived, which allows a more detailed discussion of the electronic structure of the molecule in combination with future quantum-chemical calculations. Additionally it is shown that the variation of the electron density along the vibrational motion at low vibrational levels can be as large as the variation for the electronic transition A0⁺ -X¹Σ⁺ in the case of PbS. The magnetic hyperfine structure of ²⁰⁷Pb is resolved in a molecule for the first time. The coupling parameter of PbS is compared with that of the isovalent molecule TlCl.     

Hyperfine structure of SrCl X2∑+ by microwave—optical polarization spectroscopy

The hyperfine structure of the X²∑⁺, υ = 0 state of ⁸⁸Sr³⁵Cl has been investigated using microwave—optical polarization spectroscopy. Resolution of the hyperfine structure in transitions between low-lying rotational states has allowed the first determination of magnetic dipole and electric quadrupole coupling constants. The results are: b = 18.663(89) MHz, c = 7.72(30)MHz, and eqQ = 3.96(84) MHz.     

CAS SCF Cl calculations for the 3Σ−g, 1Σ+g, 3Σ+u, and 5Δu states of Sc2

CAS SCF CI (SD) calculations have been carried out for the ³Σ^?_g, ¹Σ⁺_g, ³Σ⁺_u, and ⁵Δ_u states of Sc₂ using large gaussian basis sets. The ³Σ^?_g, ¹Σ⁺_g, and ³Σ⁺_u states arise from the ²D(4s² 3d¹) + ²D(4s² 3d¹) limit of Sc₂ and are found to be only weakly bound (D_c ≈ 0.06 eV and R_c ≈ 8.0a₀). The ⁵Δ_u state arises from the ²D(4s² 3d¹) + ⁴F(4s¹ 3d¹ 4p¹) atomic limit. This state is found to be strongly bound relative to its limits (D_c ≈ 0.8 eV and R_c ≈ 7.0a₀).     

Stability constants of the Li+, Na+, H3O+, NH4+, Ag+, and K+ complexes of the cone conformer of tetraethyl p-tert-butyltetrathiacalix[4]arene tetraacetate in nitrobenzene saturated with water

Abstract  

From extraction experiments in the two-phase water–nitrobenzene system and γ-activity measurements, the stability constants of the tetraethyl p-tert-butyltetrathiacalix[4]arene tetraacetate (cone)·M⁺ complexes (M⁺ = Li⁺, H₃O⁺, NH₄ ⁺, Ag⁺, or K⁺) were determined in water-saturated nitrobenzene. It was found that these constants increase in the cation order NH₄ ⁺ < K⁺ < H₃O⁺ < Ag⁺ < Li⁺ < Na⁺.     

Molecular structure and character of bonding of mono and divalent metal cations (Li+, Na+, K+, Mg2+, Ca2+, Zn2+, and Cu+) with guanosine: AIM and NBO analysis

The B3LYP/6-311++G (d,p) density functional approach was used to study the gas-phase metal affinities of Guanosine (ribonucleoside) for the Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Zn²⁺, and Cu⁺ cations. In this study we determine coordination geometries, binding strength, absolute metal ion affinities, and free energies for the most stable products. We have also compared the results for Guanosine, with our previously reported results for 2′-Deoxyguanosine. Based on the results, it is obvious that MIA is strongly dependent on the charge-to-size ratio of the cation. Guanosine interacts more strongly with Zn²⁺ than do with Mg²⁺, Ca²⁺, and Cu⁺ and therefore stronger interactions lead to higher MIA. In both free molecules and their complexes, the Syn orientation of the base is stabilized by an intramolecular O5′–H···N3 hydrogen bond and the anti orientation of the base is stabilized by an intramolecular C–H···O hydrogen bond formed between the (C8-H8) and the O5′ atom of the sugar moiety. It is also interesting to mention that linear correlation between calculated MIA values and the atomic numbers (Z) of the metal ions of Li⁺, Na⁺, and K⁺ were found. Furthermore, the influences of metal cationization on the strength of the N-glycosidic bond, torsion angles, angle of pseudorotation (P), and intramolecular C–H···O and O–H···O hydrogen bonds have been studied. Natural bond orbital (NBO) analysis was performed to calculate the charge transfer and natural population analysis of the complexes. Quantum theory of atoms in molecules (QTAIM) was also applied to determine the nature of interactions.     

Solubility and Ionic Processes in the Cu X 2? MX ?H2O ( X ?=Cl?, Br?; M +=Li+, Na+, K+, NH4+, Cs+) Systems

 Solubility isotherms in the CuBr₂−MBr−H₂O (M ⁺ = Li⁺, Na⁺, Cs⁺) systems at 298.15 K were measured. The results together with other available literature data for copper chloride and bromide systems were treated by hydration analysis, and comparative discussion of ionic processes taking place in the respective saturated solutions was performed.     

Solubility and Ionic Processes in the Cu X 2? MX ?H2O ( X ?=Cl?, Br?; M +=Li+, Na+, K+, NH4+, Cs+) Systems

Summary.  Solubility isotherms in the CuBr₂−MBr−H₂O (M ⁺ = Li⁺, Na⁺, Cs⁺) systems at 298.15 K were measured. The results together with other available literature data for copper chloride and bromide systems were treated by hydration analysis, and comparative discussion of ionic processes taking place in the respective saturated solutions was performed. Corresponding author. E-mail: jitka@prfdec.natur.cuni.cz Received August 6, 2002; accepted (revised) November 29, 2002 Published online April 3, 2003     

Studies on primary hydrated complexes of Li+, Na+ and K+ ions by the extended Hückel method

The potential curves for aquacomplexes of Li⁺, Na⁺ K⁺ ions with the coordination numbers, n, equal to 4, 6 and 8 have been calculated by the extended Hückel method. The equilibrium values of the hydrated shell radius and the binding energy have been determined. The complexes of Li⁺ with n = 6 and Na⁺ and K⁺ with n = 8 were found to be the most advantageous energetically. As could be expected the contribution of the 3d-orbitals to the binding for the K⁺ion is much more considerable than for the Na⁺ion. The character of the potential curves for aquacomplexes of sodium and potassium ions is quite different. In the case of the K⁺ion the curves are found to be very smooth and slowly decreasing with distance, which can be attributed to the poor hydratability of this ion and the “loosening” of water structure by it.     

Ab initio MO calculations on the stable conformations and their binding energies of the ion-molecule complexes: Ion = H+, Li+, Na+, K+ Be2+, and molecule = CO and N2

The most stable conformation of ion-molecule complexes involving a CO molecule were surveyed by the use of Hartree-Fock (HF) MO and third-order Moller-Plesset perturbation (MP3) methods with a 6–31G* basis set ion = H⁺, Li⁺, Na⁺, K⁺, Bc²⁺, Mg²⁺, and Ca²⁺. The MP3 level of theory reveals the ion-CO conformation in which the ion bonds to a carbon atom of CO to be the most stable; these MP3 results are contrary to the HF ones. Binding energies of ion-molecule complexes involving CO and N₂ were computed; MP3 energies are in good agreement with the experimental ones. The computed binding energies of cation-N₂ are about one-third of cation-NH₃ due to the absence of dipole moment and the smaller polarizability of N₂. The decrease in binding energy in cation-CO and -N₂ complexes, with increasing cation size, is mainly caused by the decrease of the electrostatic and polarization stabilizations.     

Synthesis and Efficiency of Poly(Acryl- p-Nitrophenylamidrazone- p-Nitrophenylhydrazide) Chelating Fibre for Pre-Concentration and Separation of Trace Concentrations of Bi 3+, In 3+, Sn 4+, Ga 3+ and Ti 4+

A new poly(acryl-p-nitrophenylamidrazone-p-nitrophenylhydrazide) chelating fibre was synthesized from polyacrylnitrile fibre, and the structure of the chelating fibre was determined with the help of the FT-IR spectrum. The parameters influencing the efficiency of the fibre for concentrating trace amounts of Bi³⁺, In³⁺, Sn⁴⁺, Ga³⁺ and Ti⁴⁺, including sample acidity during enrichment, flow rate, adsorptive capacity, re-usability, interfering ions and desorption conditions were investigated. Trace Bi³⁺, In³⁺, Sn⁴⁺, Ga³⁺ and Ti⁴⁺ were enriched and separated from real sample solutions and detected using inductively coupled plasma optical emission spectrometry (ICP-OES) with satisfactory results. The experiments show that the method is rapid, precise, simple and convenient to use.     

Franck-Condon factors and r -centroids for the E 1Πu- X 1Σ g+ system of Ag2

An array of Franck-Condon factors and r-centroids is reported for the bands of the E ¹Π_u-X ¹Σ _g ⁺ system of the Ag₂ molecule. Both parameters were calculated using the Morse and Rydberg-Klein-Rees potentials. The results showed a reasonable agreement between the two sets of data for transitions, including lower vibrational levels (v ≤ 6). Differences appear with increasing v, but two sets of calculated Franck-Condon factors follow the same pattern. The predicted intensity distribution was compared with the estimated band intensity in the experimental spectrum. The text was submitted by the authors in English.     

Ã2Σ+ → X̃+Π Emission spectra of the phosphaethyne cations,HCP+ and DCP+

The electron impact excited òΣ⁺ → X?⁺Π emission spectra of HCP⁺ and DCP⁺ have been observed. The spin-orbit split 0-0 band has maxima at 593.7 and 599.0 nm for HCP⁺ and 593.6 and 598.8 nm for DCP⁺. Short progressions in the V₃(CP) vibration are observed. a₀, v₃ and the upper-state lifetime are determined.     

Solvent extraction of H3O+, NH4+, Ag+, K+, Rb+ and Tl+ into nitrobenzene by using cesium dicarbollylcobaltate in the presence of a hexaarylbenzene-based receptor

From extraction experiments and γ-activity measurements, the extraction constants corresponding to the general equilibrium M⁺(aq) + 1·Cs⁺(nb) \rightleftarrows \rightleftarrows 1·M⁺(nb) + Cs⁺(aq) taking part in the two-phase water–nitrobenzene system (1 = hexaarylbenzene-based receptor; M⁺ = H₃O⁺, NH₄ ⁺, Ag⁺, K⁺, Rb⁺, Tl⁺; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Furthermore, the stability constants of the ML⁺ complex species in nitrobenzene saturated with water were calculated; they were found to increase in the series of Rb⁺ < K⁺ < Ag⁺, Tl⁺ < H₃O⁺, NH₄ ⁺.     

Electron spin density distribution in the CO+, CO2− and O2− radicals as a function of geometry

The standard INDO method has been used to calculate the electron spin density distribution and isotropic Fermi contact hyperfine coupling in the radicals CO⁺, CO₂^?, and O₂^?. Bond lengths and angle (for CO₂^?) have been varied over a reasonable range. Geometrical effects are found to have a relatively small influence on the calculated values which do agree closely with the experimental data.     

Rotational analysis of the a3Π0+,1-X1Σ+ emission systems of GeH+

New emission systems have been observed from the helium afterglow reaction of GeH₄ in the 520–610 nm region. On the basis of the rotational analysis, they were assigned to the a ³Π_0⁺-X¹Σ⁺ and a³Π₁-X¹Σ⁺ subsystems of GeH⁺. Spectroscopic constants have been determined for the GeH⁺ (a³Π_0⁺, a³Π₁, X¹Σ⁺) states.     

Complexing ability of pesticides and related compounds. Formation and stability in aqueous solution of H+ , Li+, Na+, K+, Mg2+ and Ca2+ phenoxyacetate complexes at different temperatures and ionic strengths

The formation constants of Li⁺, N⁺, K⁺, Mg²⁺ and Ca²⁺ phenoxyacetate complexes were determined potentiometrically using an (H⁺)-glass electrode at 10, 25, 37 and 45°C, at several ionic strengths, in the range 0.04?I? 0.9 mol 1^?1. Simple empirical equations for the dependence of the formation constants on ionic strength were derived. From the temperature coefficients, estimates of ΔH^o and ΔS^o were obtained.     

Ligand hyperfine coupling in Mo(V) oxyhalide complexes

For a series of Mo(V) oxyhalide complexes MoOL ₅ ^2? (L = F, Cl, Br, I), interpretation of the ligand hyperfine coupling parameters (A ^L tensor components) is considered. The role of spin polarization is elucidated and the effect of charge transfer states is taken into account. The A ^L tensor components were calculated using the covalency parameters derived from experimental EPR and optical spectroscopy data for compounds under study (inverse problem of EPR spectroscopy).     

Optical oscillator strengths of 3p63d 2D → 3p53d22po, 2Do, 2Fo transitions in Co8+, Cu1O+ and Zn11+ ions

We have calculated the excitation thresholds and optical oscillator strengths (OOS) for 3p⁶3d ²D → 3p⁵3d²²po, ²Do and ²F^o transitions Co⁺⁸, Cu¹⁰⁺ and Zn¹¹⁺ ions of the potassium isoelectronic sequence using Hartree-Fock (HF) and configuration interaction (Cl) wavefunctions for both initial and final states. Our Cl values of the length and velocity form of OOS are in good agreement with each other. The trends in the oscillator strengths for the potassium isoelectronic sequence are plotted.     

Rotational analysis of the 201 and 211 bands in the Ã2Σ+-X̃ 2Π spectrum of N2O+

Analysis of new emission spectra of òΣ⁺-X? ²Π in N₂O⁺, including the forbidden components with Δν₂ = 1, have made it possible to locate all four vibronic components of the ν″₂ = 1 manifold. Principal rotational constants and spinvibronic terms are given. A previous estimate of the Renner parameter is revised to a value of ?0.179 ± 0.002.