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     

Experimental Determination of the Isotherm at 15°C of the System Mg2+/Cl?, SO42–H2O

 The diagram of the ternary system Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O was established at 15°C by means of analytical and conductimetric measurements. Three compounds were found in this diagram, which are MgSO₄·6H₂O, MgSO₄·7H₂O, and MgCl₂·6H₂O. The solubility field of MgSO₄·7H₂O is important whereas those of MgSO₄·6H₂O and MgCl₂·6H₂O are small. The compositions (mass-%) of the two invariant points determined by the two methods are: MgSO₄:MgCl₂=2.73:33.80 and MgSO₄: MgCl₂=3.38:28.91. Both the measured and the calculated isotherm at 15°C have been used for modelling of the diagram Mg²⁺/Cl⁻, SO₄ ²⁻–H₂O between 0 and 35°C. The polythermal invariant point was approximately located between 15 and 10°C.     

Electronic structure and reactivity of PO 43? , P2O 74? phosphate and SO 42? , S2O 72? sulfate anions

Group-theoretical analysis and molecular orbital methods were used to obtain (in analytical form) the electronic structure and reactivity of the PO ₄ ³⁻ , SO ₄ ²⁻ and P₂O ₇ ⁴⁻ , S₂O ₇ ²⁻ anions. The reactivity of the anions is dictated by the availability of lone electron pairs on the top quasidegenerate MOs in the form of linear combinations of group orbitals from atomic orbitals (AOs) of peripheral oxygen atoms for PO ₄ ³⁻ , SO ₄ ²⁻ and the central (bridging) atom for P₂O ₇ ⁴⁻ , S₂O ₇ ²⁻ . These electron pairs are responsible for the donor-acceptor interactions during complexation, clustering, and other (addition, substitution, etc.) reactions. Original Russian Text Copyright ? 2005 V. A. Zasukha, A. P. Shpak, V. V. Trachevskii, and E. V. Urubkova __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 3, pp. 405–415, May–June, 2005.     

Synthesis, structural characterization and properties of a 3D infinitely extended structural rare earth coordination compound of K3{[Sm(H2O)7]2Na[α-SiW11O39Sm(H2O)4]2} · 14 H2O· 14 H2O

A 3D infinitely extended structural rare earth coordination compound with a formula of K₃{[Sm(H₂O)₇]₂Na[α-SiW₁₁O₃₉Sm(H₂O)₄]₂}·14H₂O has been synthesized by reaction of Sm₂O₃, HClO₄, NaOH with α-K₈SiW₁₁O39·nH₂O, and characterized by IR, UV spectra, ICP, TG-DTA, cyclic voltammetry, variable-temperature magnetic susceptibility and X-ray single-crystal diffraction. X-ray single-crystal diffraction indicates that the title compound crystallizes in a triclinic lattice, Pī space group, with a = 1.2462(3) nm, b = 1.2652(3) nm, c = 1.8420(4) nm, α = 87.45(3)°, β = 79.91(3)°, γ= 82.57(3)°, Z = 1, R₁ = 0.0778, wR₂ = 0.1610. Structural analysis reveals that Sm³⁺(1) coordination cation has incorporated into the vacant site of [α-SiW11O₃₉]⁸⁻ entity, forming the [α- SiW₁₁O₃₉Sm(H₂O)₄]⁵⁻ subunit. The two adjacent [α-SiW₁₁O₃9Sm(H₂O)4]⁵⁻ subunits are combined with each other through two Sm(1)-O-W bridges accompanying the formation of dimmer structural unit [α-SiW₁₁O₃₉Sm(H₂O)₄]₂ ¹⁰⁻ of the title compound. The neighboring dimmer structural units [α-SiW₁₁O₃₉Sm(H₂O)₄]₂ ¹⁰⁻ are linked to form the 1D chainlike structure by means of two Sm³⁺(2) and a Na⁺(1) coordination cations. The K⁺(1) cations connect the 1D packing chains constructing the 2D netlike structure, and adjacent netlike layers are also grafted by K⁺(2) cations to build the novel 3D infinitely extended structure. The result of TG-DTA curves manifests that the decomposition temperature of the title polyanionic framework is 554°C. The cyclic voltammetry measurements show that the title polyanion has the two-step redox processes in aqueous solution with pH = 3.1. Variable temperature magnetic susceptibility indicates the title compound obeys the Cruie-Weiss Law in the higher temperature range from 110 to 300 K, while in the lower temperature range from 2 to 110 K the comparatively strong antiferromagnetism interactions can be observed.     

Theoretical study of the structure and stability of the Na2Cl+, NaCl 2? , Na3Cl 2+ , and Na2Cl 3? ions

The geometrical parameters, normal vibration frequencies, and thermochemical characteristics of the Na₂Cl⁺, NaCl ₂ ⁻ , Na₃Cl ₂ ⁺ , and Na₂Cl ₃ ⁻ ions in saturated vapors over sodium chloride were calculated by the ab initio methods including electron correlation. According to calculations, the Na₂Cl⁺ and NaCl ₂ ⁻ triatomic ions have a linear equilibrium D _∞h configuration. The pentaatomic ions can exist in the form of the D _∞h linear isomer, C _2v planar cyclic isomer, or D _3h bipyramidal isomer. At ∼1000 K the Na₃Cl ₂ ⁺ and Na₂Cl ₃ ⁻ ions exist predominantly in the form of the linear isomers. The energies and enthalpies of the ion-molecule reactions involving the above ions were calculated. The formation enthalpy of the ions Δ_f H ⁰(0 K) was determined: 230 ± 2 kJ/mol (Na₂Cl⁺), −96 ± 4 kJ/mol (Na₂Cl ₃ ⁻ ), −616 ± 2 kJ/mol (NaCl ₂ ⁻ ), and −935 ± 4 kJ/mol (Na₂Cl ₃ ⁻ ). Original Russian Text Copyright ? 2007 by T. P. Pogrebnaya, A. M. Pogrebnoi, and L. S. Kudin __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 6, pp. 1053–1061, November–December, 2007.     

Na+/K+-ATPase: Activity and inhibition

The aim of the study was to give an overview of the mechanism of inhibition of Na⁺/K⁺-ATPase activity induced by some specific and non specific inhibitors. For this purpose, the effects of some ouabain like compounds (digoxin, gitoxin), noble metals complexes ([PtCl₂DMSO₂], [AuCl₄]⁻, [PdCl₄]²⁻, [PdCl(dien)]⁺, [PdCl(Me₄dien)]⁺), transition metal ions (Cu²⁺, Zn²⁺, Fe²⁺, Co²⁺), and heavy metal ions (Hg²⁺, Pb²⁺, Cd²⁺) on the activity of Na⁺/K⁺-ATPase from rat synaptic plasma membranes (SPM), porcine cerebral cortex and human erythrocytes were discussed. The article is published in the original.     

Structure of uranyl complexes with acetylenedicarboxylic acid, K(H5O2)[UO2(OOCC≡CCOO)2 · H2O] · 2H2O and Cs2[UO2(OOCC≡CCOO)2 · H2O] · 2H2O

Uranyl complexes with acetylenedicarboxylic acid, K(H₅O₂)[UO₂L₂H₂O] · 2H₂O (I) and Cs₂[UO₂L₂H₂O] · 2H₂O (II), L²⁻ = C₄O ₄ ²⁻ were prepared for the first time. The composition and structure of the complexes were determined by X-ray diffraction. The crystal data are as follows: a = 16.254(12) ?, b = 13.508(8) ?, c = 7.683(6) ?, β = 90.91(7)°, space group C2/c, V = 1687(2) ?³ (I); a = 7.0745(10), b = 18.4246(10), c = 13.1383(10) ?, space group Abm2, V = 1712.5(3) ?³ (II). The structures of I and II are based on [UO₂L₂H₂O] _n ²⁻ anionic chains stretched along the [101] direction (I) or [010] direction (II). In I and II, the uranium coordination polyhedron is a pentagonal bipyramid in which the equatorial environment of the uranyl ions is formed by the oxygen atoms of the four L²⁻ anions and the water molecule. The L²⁻ anions in I and II are bidentate bridging ligands connecting two uranium atoms that are next to each other in the anionic chain; their coordination capacity is equal to 2. In I, the K⁺ and H₅O ₂ ⁺ cations are outer-sphere species. The latter form hydrogen bonds combining the anionic chains shifted by translation b with respect to each other. The [UO₂L₂H₂O] _n ²⁻ chains in I are surrounded by the potassium and oxonium cations; in II, these are combined by hydrogen bonds into anionic layers between which Cs⁺ cations are arranged. The IR spectrum of compound II was measured and interpreted. Original Russian Text ? I.A. Charushnikova, A.M. Fedoseev, N.A. Budantseva, I.N. Polyakova, Ph. Moisy, 2007, published in Koordinatsionnaya Khimiya, 2007, Vol. 33, No. 1, pp. 63–69.     

Synthesis and Structure of the Alkoxido-Titanium Pentamolybdate (nBu4N)3[(iPrO)TiMo5O18]: An Entry into Systematic TiMo5 Reactivity

The alkoxido-titanium pentamolybdate [(ⁱPrO)TiMo₅O₁₈]³⁻ (1) has been obtained as its tetrabutylammonium (TBA) salt by hydrolysis of a mixture containing (TBA)₂[Mo₂O₇], (TBA)₄[Mo₈O₂₆] and Ti(OⁱPr)₄ in MeCN and has been characterised by ¹H, ¹³C, ¹⁷O, ⁴⁹Ti and ⁹⁵Mo NMR and FTIR spectroscopy, electrospray ionisation mass spectrometry, elemental microanalysis and single-crystal X-ray crystallography. The Lindqvist-type structure is derived from [Mo₆O₁₉]²⁻ by replacement of {Mo=O}⁴⁺ by {(ⁱPrO)Ti}³⁺ and shows bond alternation in the TiMo₃O₄ rings, with average bond distances of 1.956(8) ? for Ti–O(Mo), 1.832(7) ? for Mo–O(Ti), 1.943(7) ? for Mo_eq–O(Mo_ax) and 1.910(6) ? for Mo_ax–O(Mo_eq), while the increase in charge results in a decrease in ¹⁷O NMR chemical shift for terminal Mo=O groups from δ 933 for [Mo₆O₁₉]²⁻ to δ 875 and 857 for 1 and a shift in ν_Mo=O from 951 cm⁻¹ for [Mo₆O₁₉]²⁻ to 930 cm⁻¹ for 1. The main peaks in the negative-ion electrospray ionisation mass spectrum of (TBA)₃ 1 could be assigned to ion aggregates containing 1 or fragments derived from 1, including {(TBA)₂[(ⁱPrO)TiMo₅O₁₈]}⁻, {(TBA)[(ⁱPrO)TiMo₅O₁₈]}²⁻, {(ⁱPrO)TiMo₂O₈}⁻, {TiMo₅O₁₈}²⁻, {TiMo₄O₁₅}²⁻ and {Mo₃O₁₀}²⁻.     

Low-temperature heat capacity and standard enthalpy of formation of neodymium glycine perchlorate complex [Nd2(Gly)6(H2O)4](ClO4)6·5H2O

Rare-earth perchlorate complex coordinated with glycine [Nd₂(Gly)₆(H₂O)₄](ClO₄)₆·5H₂O was synthesized and its structure was characterized by using thermogravimetric analysis (TG), differential thermal analysis (DTA), chemical analysis and elementary analysis. Its purity was 99.90%. Heat capacity measurement was carried out with a high-precision fully-automatic adiabatic calorimeter over the temperature range from 78 to 369 K. A solid-solid phase transformation peak was observed at 256.97 K, with the enthalpy and entropy of the phase transformation process are 4.438 kJ mol⁻¹ and 17.270 J K⁻¹ mol⁻¹, respectively. There is a big dehydrated peak appears at 330 K, its decomposition temperature, decomposition enthalpy and entropy are 320.606 K, 41.364 kJ mol⁻¹ and 129.018 J K⁻¹ mol⁻¹, respectively. The polynomial equations of heat capacity of this compound in different temperature ranges have been fitted. The standard enthalpy of formation was determined to be −8023.002 kJ mol⁻¹ with isoperibol reaction calorimeter at 298.15 K.     

Chromium(III) Hydroxide Solubility in the Aqueous K+-H+-OH?-CO2-HCO 3? -CO 32? -H2O System: A?Thermodynamic Model

Chromium(III)-carbonate reactions are expected to be important in managing high-level radioactive wastes. Extensive studies on the solubility of amorphous Cr(III) hydroxide solid in a wide range of pH (3–13) at two different fixed partial pressures of CO₂(g) (0.003 or 0.03 atm.), and as functions of K₂CO₃ concentrations (0.01 to 5.8 mol⋅kg⁻¹) in the presence of 0.01 mol⋅dm⁻³ KOH and KHCO₃ concentrations (0.001 to 0.826 mol⋅kg⁻¹) at room temperature (22±2 °C) were carried out to obtain reliable thermodynamic data for important Cr(III)-carbonate reactions. A combination of techniques (XRD, XANES, EXAFS, UV-Vis-NIR spectroscopy, thermodynamic analyses of solubility data, and quantum mechanical calculations) was used to characterize the solid and aqueous species. The Pitzer ion-interaction approach was used to interpret the solubility data. Only two aqueous species [Cr(OH)(CO₃)₂²⁻ and Cr(OH)₄CO₃³⁻] are required to explain Cr(III)-carbonate reactions in a wide range of pH, CO₂(g) partial pressures, and bicarbonate and carbonate concentrations. Calculations based on density functional theory support the existence of these species. The log ₁₀ K° values of reactions involving these species [{Cr(OH)₃(am) + 2CO₂(g)⇌Cr(OH)(CO₃)₂²⁻+2H⁺} and {Cr(OH)₃(am) + OH⁻+CO₃²⁻ ⇌Cr(OH)₄CO₃³⁻}] were found to be −(19.07±0.41) and −(4.19±0.19), respectively. No other data on any Cr(III)-carbonato complexes are available for comparisons.     

Solvent/substrate effects on the micelle-catalyzed aquation reactions of some iron(II) phenanthroline complexes, I. Influence of water and acid on the aquation of Fe(Ph2Phen)32+ in acetone

The effects of a substrate additive, H⁺ and solvents (water and acetone), on the micelle-catalyzed aquation of tris-(4,7-diphenyl-1, 10-phenanthroline)iron(II), Fe(Ph₂Phen)₃ ²⁺, have been investigated using^#Triton X-100 micelles. The k₀ vs. [TX-100] profiles at fixed [H₂O] are structured, exhibiting maxima. Catalytic factors of 46.6–171.7 are observed for 5.56×10⁻²≤[H₂O] 55.60×10⁻² mol dm⁻³. On the other hand, at fixed [H⁺], the k₀ vs. [TX-100] exhibit broad maxima. The aquation reaction is inhibited by H⁺ and catalytic factors decrease rapidly and exponentially from 422.5 to 20.9 for 0.20×10⁻³≤[H⁺]≤2.00×10⁻³ mol dm⁻³. The aquation is found to be faster (ca. 160–1200 fold) in acetone than in the aqueous medium depending on the added [H₂O]. These observations are rationalized on the basis of a proposed modified lamellar structure for the Triton X-100 (TX-100) micelles in which direct substitution of water molecules into the coordination sphere of the complex occurs.     

Protonation of the acyclic tetraaza metallocomplex of gold(III) [Au(C9H19N4)]2+ in aqueous solution. Synthesis and crystal and molecular structure of [Au(C9H20N4)](H5O2)(ClO4)4

Protonation equilibrium has been studied for the acyclic gold(III) tetraaza metallocomplex [AuB]²⁺ [B = N, N′-bis(2-aminoethyl)-2,4-pentanediiminato(1−)] in aqueous solution. The synthetic procedure is described. The crystal and molecular structure of the protonated form of the [AuHB](H₅O₂)(ClO₄)₄ complex has been determined. Monoclinic crystals with unit cell dimensions a = 11.964(2) Å, b = 13.789(3) Å, c = 15.496(3) Å, β = 109.00(3)°, V = 2417.1(8) ų, Z = 4, ρcalc = 2.243 g/cm³, space group P2₁/n. The structure is built of nearly planar [Au(C₉H₂₀N₄)]³⁺ complex cations, (H₅O₂)⁺ cations, and [ClO₄]⁻ anions. The gold atom coordinates four nitrogen atoms of the ligand, forming a square plane. The six-membered chelate ring of the ligand is protonated at the central β-carbon atom and contains imine C=N bonds. The oxygen atoms of the perchlorate ions are hydrogen bonded to the (H₅O₂)⁺ dihydroxonium ion and to the nitrogen atoms of the NH₂ groups of the [AuHB]³⁺ cation. Original Russian Text Copyright ? 2005 by V. A. Afanasieva, L. A. Glinskaya, R. F. Klevtsova, and I. V. Mironov __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 5, pp. 909–915, September–October, 2005.     

Kinetics of the Formation of the Blue Complex CrO(O2)2 Formed by Dichromate and H2O2 in Acid Solutions. A Stopped-Flow Investigation Using Rapid-Scan UV-VIS Detection

 The kinetics of the CrO(O₂)₂ formation by H₂O₂ and Cr₂O₇ ²⁻ in aqueous acidic media was measured at 293 ± 2 K in a pH range between 2.5 and 3.3. Using the stopped-flow method with rapid scan UV-VIS detection, the rate law of the formation of CrO(O₂)₂ was determined. For the media HClO₄, HNO₃ and CH₃COOH, the reaction order in the Cr₂O₇ ²⁻ concentration was found to be 0.5. For [H₂O₂] as well as for [H⁺], the reaction was first order in all acids used. In HCl and H₂SO₄ media the reaction was first order in Cr₂O₇ ²⁻. At T = 293 ± 2 K the rate constant for the formation of Cr(O)(O₂)₂ was found to be (7.3 ± 1.9) · 10² M^−3/2 s⁻¹ in HClO₄.     

Fac-mer equilibria of coordinated iminodiacetate (IDA2?) in ternary CuII(ida)(H?1B)? complex formation (B = imidazole, benzimidazole) in aqueous solution

pH potentiometric and spectrophotometric investigations on the complex formation equilibria of Cu^II with iminodiacetate (ida²⁻) and heterocyclic N-bases, viz. imidazole and benzimidazole (B), in aqueous solution in binary and ternary systems using different molar ratios of the reactants indicated the formation of complexes of the types, Cu(ida), Cu(ida)(OH)⁻, (ida)Cu(OH)Cu(ida)⁻, Cu(B)²⁺, Cu(H^-1B)⁺, Cu(ida)(H₋₁B)⁻, (ida)Cu(B)Cu(ida) and (ida)Cu(H₋₁B)Cu(ida)⁻. Formation constants of the complexes at 25 ±1° at a fixed ionic strength,I = 0.1 mol dm⁻³ (NaNO₃) in aqueous solution were evaluated and the complex formation equilibria were elucidated with the aid of speciation curves. Departure of the experimental values of the reproportionation constants(ΔlogK _cu) of ternary Cu(ida)(H₋₁B)⁻ complexes from the statistically expected values, despite their formation in appreciable amounts at equilibrium, were assigned tofac(f)-mer(m) equilibria of the ida²⁻ ligand coordinated to Cu^II, as the N-heterocyclic donors, (H₋₁B)⁻, coordinatetrans- to the N-(ida²⁻) atom in the binary Cu(ida) _f complex to form the ternary Cu(ida) _m (H₋₁B)⁻ complexes     

Heteropoly Complexes Na0.5Cs2 ? x[H0.5 ? xM

Crystals of novel heterepoly complexes (HPC) Na_0.5Cs_{2 − x} [H_{0.5 − x} M _x ^II X^III(OH)₆Mo₆O₁₈] · 7−8H₂O (M^II = Fe, Mn; X^III = Cr, Al) are synthesized. Crystal structures of the complexes Na_0.5Cs_{2 − x} [H_{0.5 − x} Fe_xCr(OH)₆Mo₆O₁₈] · 7H₂O (I) (x = 0.19) and Na_0.5Cs_{2 − x} [H_{0.5 − x} Mn_xAl(OH)₆Mo₆O₁₈] · 8H₂O (II) (x = 0.22) are determined (space group Pbcn, Z = 8, a = 23.023(4) Å, b = 22.064(4) Å, c = 11.606(3) Å, V = 5895.66 ų for I and a = 22.972(9) Å, b = 22.002(8) Å, c = 11.543(5) Å, V = 5834.18 ų for II, respectively). The [X^III(OH)₆Mo₆O₁₈]³⁻ ligands were found to be coordinated in monodentate fashion to M atoms due to the participation of a terminal O atom of the cis-MoO₂ group in coordination with the Fe and Mn atoms, which was confirmed by IR data. __________ Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 9, 2005, pp. 663–676. Original Russian Text Copyright ? 2005 by Gavrilova, Molchanov.     

Kinetic and mechanistic studies on the electron-transfer reactions between diaquabisethylenediaminecobalt(III) and ethylenediaminetetraacetatocobaltate(III) with promazine in acidic aqueous media

The kinetics of the electron-transfer reactions between promazine (ptz) and [Co(en)₂(H₂O)₂]³⁺ in CF₃SO₃H solution ([Co^III] = (2–6) × 10⁻³ m, [ptz] = 2.5 × 10⁻⁴ m, [H⁺] = 0.02 − 0.05 m, I = 0.1 m (H⁺, K⁺, CF₃SO ₃ ⁻ ), T = 288–308 K) and [Co(edta)]⁻ in aqueous HCl ([Co^III] = (1 − 4) × 10⁻³ m, [ptz] = 1 × 10⁻⁴ m, [H⁺] = 0.1 − 0.5 m, I = 1.0 m (H⁺, Na⁺, Cl⁻), T = 313 − 333 K) were studied under the condition of excess Co^III using u.v.–vis. spectroscopy. The reactions produce a Co^II species and a stable cationic radical. A linear dependence of the pseudo-first-order rate constant (k _obs) on [Co^III] with a non-zero intercept was established for both redox processes. The rate of reaction with the [Co(en)₂(H₂O)₂]³⁺ ion was found to be independent of [H⁺]. In the case of the [Co(edta)]⁻ ion, the k _obs dependence on [H⁺] was linear and the increasing [H⁺] accelerates the rate of the outer-sphere electron-transfer reaction. The activation parameters were calculated as follows: ΔH ^≠ = 105 ± 4 kJ mol⁻¹, ΔS ^≠ = 93 ± 11 J K⁻¹mol⁻¹ for [Co(en)₂(H₂O)₂]³⁺; ΔH ^≠ = 67 ± 9 kJ mol⁻¹, ΔS ^≠ = − 54 ± 28 J K⁻¹mol⁻¹ for [Co(edta)]⁻.     

Technology of obtaining of potassium dihydrophosphate in the system with salting-out

The technology of producing of potassium dihydrophosphate (and potassium metaphosphate) mineral fertilizer in multicomponent system with salting-out is described; this technology is the result of investigation of multicomponent system K⁺, (C₂H₅)₂NH₂⁺ // Cl⁻, H₂PO₄⁻-H₂O, diagrams of the system condition and technological scheme are given; theoretical estimation of useful product yield agrees with experimental data.     

One-and two-dimensional silver-tetramethylpyrazine coordination polymers with uncoordinated anions: Synthesis and structure of [Ag(Me4Pyz)]PF6 and [Ag2(Me4Pyz)3](BF4)2·H2O

Coordination polymers [Ag(Me₄Pyz)] PF₆(I) and [Ag₂(Me₄Pyz)₃](BF₄)₂·H₂O (II) have been synthesized, and their structures have been determined. The crystals of I are monoclinic, space group C2/c, a = 9.440(2) ?, b = 10.587(2) ?, c = 13.165(3) ?, β= 107.19(3)°, V = 1257.0(5) ?³, d = 2.056 g/cm³, Z = 4. The crystals of II are monoclinic, space group P2₁/n, a = 13.062(3) ?, b = 12.259(2) ?, c = 18.996(4) ?, β = 97.73(3)°, V = 3014.1(11)?³, ρ = 1.798 g/cm³, Z = 4. The structure of I is built of linear polymeric cations [Ag(C₈H₁₂N₂)] _∞ ⁺ and octahedral anions [PF₆]⁻. Upon the interaction of tetramethylpyrazine molecule with Ag⁺ ions, intersecting polymeric chains [Ag(C₈H₁₂)] _∞ ⁺ (1D polymer) are formed extending in mutually perpendicular diagonal directions. The structure of II consists of layers (2D polymers) formed by fused sixmembered rings. These rings consist of Ag⁺ ions linked by bridging ligands Me₄Pyz. Original Russian Text ? Yu.V. Kokunov, Yu.E. Gorbunova, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 5, pp. 743–750.     

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.