Pyrazolat und Tetrazolat als Brückenliganden in [Pt(pz)2]3, [Pt(pz)2]∞ und [Pt(tz)2]∞ Die Kristallstruktur von [Pt(pz)2]3

Pyrazolat and Tetrazolat as Bridging Ligands in [Pt(pz)₂]₃, [Pt(pz)₂]_∞, and [Pt(tz)₂]_∞ Crystal Structure of [Pt(pz)₂]₃ . [Pt(pz)₂(Hpz)₂]₂ (Hpz = pyrazole) suspended in mesitylene decomposes at 185°C in a sealed tube to [Pt(pz)₂]₃ and [Pt(pz)₂]_∞. The reaction of K₂PtCl₄ with K(pz) under hydrothermal conditions at 150°C yields [Pt(pz)₂H₂O]_∞. [Pt(tz)₂ H₂O]_∞ (Htz = tetrazole) is obtained at 25°C from K₂PtCl₄ and Li(tz) in water. [Pt(pz)₂]₃ crystallizes in the tetragonal space group I4₁/a with a = 1694.9 pm, c = 3127.5 pm and Z = 16. It forms a ring structure with the symmetry D_3h. In the structure the Pt atoms are each bridged by two pyrazolato ligands. Short but nonbonding Pt? Pt distances range from 303.4 pm to 306.7 pm. The average Pt? N distance is 201 pm.     

Asymmetric salt effects on anion/cation reactions: A comparative study of the [Fe(CN)6]4− + [Co(NH3)5pz]3+ and [Ru(NH3)5pz]2+ + [Co(C2O4)3]3− reactions

The kinetics of electron transfer reactions between [Fe(CN)₆]^4? and [Co(NH₃)₅pz]³⁺ and between [Ru(NH₃)₅pz]²⁺ and [Co(C₂O₄)₃]^3? was studied in concentrated salt solutions (Na₂SO₄, LiNO₃, and Ca(NO₃)₂). An analysis of the experimental kinetic data, k_obs, permits us to obtain the true (unimolecular) electron transfer rate constants corresponding to the true electron transfer process (precursor complex → successor complex), k_et. The variations of both, k_obs and k_et, with salt concentrations are opposite for these reactions. These opposite tendencies can be rationalized by using the Marcus–Hush treatment for electron transfer reactions. The conclusion is that the negative salt effect found for the first reaction ([Fe(CN)₆]^4? + [Co(NH₃)₅pz]³⁺) is due to the increase of the reaction and reorganization free energies when the concentration of salt increases. In the case of the second reaction ([Ru(NH₃)₅pz]²⁺ + [Co(C₂O₄)₃]^3?), the positive salt effect observed is caused by the fact that the driving force becomes more favorable when the concentration of salt increases. Thus, it is shown that for anion/cation electron transfer reactions the kinetic salt effect depends on the charge sign of the oxidant (and the reductant). © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 81–89, 2005     

Kinetics and mechanism of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) by N-bromosuccinimide in aqueous acidic medium

The kinetics of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) complex by N-bromosuccinimide (NBS) in aqueous acid and H₂O–MeOH solvent mixtures were studied spectrophotometrically over the 20–40 °C range, 0.1–0.5 mol dm^?3 ionic strength, 2.2–2.8 pH range and 0–40 wt% MeOH–H₂O solvent mixtures for a range of NBS and complex concentrations. The rate shows first-order dependence on both [NBS] and [complex] and decreases with pH over the range studied. The protonated form of N-bromosuccinimide was identified as the main reactive species. An inner-sphere mechanism involving free radicals is proposed.     

Study of the base‐catalyzed nitrito–nitro isomerization reaction ([(NH3)5Co‐ONO]2+ → [(NH3)5Co‐NO2]2+) in mixed solvents

The base‐catalyzed linkage isomerization of [Co(NH₃)₅‐ONO]²⁺ to the nitro [(NH₃)₅Co‐NO₂]²⁺ form is studied in various isodielectric water–cosolvent mixtures (methanol, ethanol, tert‐butyl alcohol, and 2‐propanol) at 298 K. In all cases, except for methanol–water mixtures, the rate constants increase with the proportion of cosolvent. Medium effects have been rationalized by using a multiparameter regression of solvent parameters which rationalizes the results obtained, including water–methanol mixtures. The experimental data, k₂, in fact, are well correlated through the following equation: where A, B, and G_exc are the acidity parameter, the basicity parameter, and the excess Gibbs free energy of the mixture, respectively. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 410–415, 2004     

Solvothermal Synthesis,Crystal Structure and Properties of the First Organic‐templated Holmium Sulfate [C2N2H10]3[Ho2(SO4)6·2H2O]

The first organic amine‐templated holmium sulfate [C₂N₂H₁₀]₃[Ho₂(SO₄)₆·2H₂O] ( 1 ) has been synthesized solvothermally and has been structurally characterized by single‐crystal X‐ray diffraction studies, IR spectroscopic, thermogravimetric (TG) and inductivity coupled plasma (ICP) measurements. Crystal analyses of compound 1 showed a novel inorganic layer constructed from the zigzag and helical [–Ho–O–S–O–]_n chains, both of the chains are connected by μ‐2 SO₄^2– groups to form 10‐membered rings. The solvent plays an important role during the formation of 1 .     

Hydrate isomerism in [Cu(en)2(H2O)1.935]2[Fe(CN)6]·4H2O

The title compound, bis[di­aqua­bis­(ethyl­enedi­amine‐κ²N,N′)copper(II)­] hexa­cyano­iron(II) tetrahydrate, [Cu(C₂H₈N₂)₂(H₂O)_1.935]₂[Fe(CN)₆]·4H₂O, was crystallized from an aqueous reaction mixture initially containing CuSO₄, K₃[Fe(CN)₆] and ethyl­enedi­amine (en) in a 3:2:6 molar ratio. Its structure is ionic and is built up of two crystallographically different cations, viz. [Cu(en)₂(H₂O)₂]²⁺ and [Cu(en)₂(H₂O)_1.87]²⁺, there being a deficiency of aqua ligands in the latter, [Fe(CN)₆]⁴⁻ anions and disordered solvent water mol­ecules. All the metal atoms lie on centres of inversion. The Cu atom is octahedrally coordinated by two chelate‐bonded en mol­ecules [mean Cu—N = 2.016 (2) Å] in the equatorial plane, and by axial aqua ligands, showing very long distances due to the Jahn–Teller effect [mean Cu—O = 2.611 (2) Å]. In one of the cations, significant underoccupation of the O‐atom site is observed, correlated with the appearance of a non‐coordinated water mol­ecule. This is interpreted as the partial contribution of a hydrate isomer. The [Fe(CN)₆]⁴⁻ anions form quite regular octahedra, with a mean Fe—C distance of 1.913 (2) Å. The dominant intermolecular interactions are cation–anion O—H⋯N hydrogen bonds and these inter­actions form layers parallel to (001).     

Micellar effects on a ligand substitution reaction: Kinetics of the formation of [Fe(CN)5(μ‐pz)Ru(NH3)5]−, from [Fe(CN)5H2O]3− and [Ru(NH3)5pz]2+, in the presence of anionic micelles

The kinetics of substitution of H₂O by Ru(NH₃)₅pz²⁺ (pz = pyrazine) in Fe(CN)₅H₂O^3? have been studied in micellar aqueous solutions of sodium dodecylsulfate (SDS). Experimental results are discussed by using an approach based on the transition‐state theory. This approach is better than others based on the pseudophase model, which can also be used, because it is able to give a clear meaning to the parameters of the model. Trends in the observed reactivity are explained by a change in the degree of association of one of the reactants to the micelles (Ru(NH₃)₅pz²⁺ in the present work). This association is governed by an equilibrium constant that depends on the electrostatic potential at the surface of the micelles. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 627–633, 2004     

Kinetics of aquation of cis-aquabromo-bis(ethylenediamine) complexes of cobalt(III) and chromium(III) in binary aqueous mixtures

Summary The kinetics of aquation of cis-[Co(en)₂(H₂O)Br]²⁺ and cis-[Cr(en)₂(H₂O)Br]²⁺ (en = ethylenediamine) were investigated in aqueous mixtures of MeOH, EtOH, i-PrOH and t-BuOH. The values of transfer functions corresponding to the transfer of reactants and activated complex from water to the solvent mixtures were evaluated from kinetic measurements and from solubilities of the complex salt. Analysis of the solvent effect confirmed a common I_d mechanism for the aquation of the Co^III and Cr^III complexes.     

Kinetics of the solvolysis of chloropenta-amminecobalt(III) ions in mixtures of water with t-butyl alcohol or with 2-methoxyethanol

Summary As the transition state for the solvolysis of [Co(NH₃)₅Cl]²⁺ ions is known to have Cl^- ions in a situation closely similar to that in the bulk solvent, the kinetics of this solvolysis have been investigated for comparison in H₂O with added cosolvents of low and high hydrophobicities. A linear variation of log(rate constant) with the reciprocal of the dielectric constant is found with the former, but not with the latter cosolvent. Maxima in the enthalpies and entropies of activation found using the more hydrophobic cosolvent appear at solvent compositions where extrema occur in the physical properties influenced by structural changes in the solvent. The application of a free energy cycle to the solvolysis in H₂O and in the mixtures shows that the emergent solvated cobalt(III) ion in the transition state is more stabilised in the latter than [Co(NH₃)₅Cl]²⁺ with both cosolvents. The application of such a cycle to cases where the initial state is destabilised in the mixture is discussed.     

Kinetics of aquation of cis- and trans-chloro-nitrobis(ethylenediamine) cobalt(III) ion in aqueous mixtures of ethylene carbonate and propylene carbonate

Summary The kinetics of aquation of cis- and trans-[Co(en)₂-NO ₂Cl] ⁺ were investigated in quasi-isodielectric aqueous mixtures of ethylene carbonate (EC) and propylene carbonate (PC) over a range of temperatures. Transfer Gibbs energies of reactant and transition state from H₂O to aqueous mixtures of EC were evaluated from kinetic measurements and the solubilities of the complex salt. An analysis of the solvent effect on the solvation of the initial (IS) and transition (TS) state reveals that their stabilization by non-aqueous cosolvent is due to predominant ion-dipole and dispersion interactions.     

Solvent extraction of uranium(VI) by p-tert-butylcalix[n]-arene acetate

The solvent extraction of U(VI) by p-tert-butylcalix[n]-arene acetate (H _n L) (n=4, 6, 8) has been studied. The effects of acidity in aqueous phase and concentration of extractant in organic phase on the distribution ratio were examined. It has been found that the distribution ratio is proportional to [H⁺]⁻² and [H _n L]_(O) and the extracted complex species is UO₂H _n ⁻²L. The equilibrium constants of the extraction reactions have been determined. The reaction mechanism is discussed.     

Synthesis and Characterization of the Mn(II) Complex of [15]aneN5

The complex Mn[15]aneN₅CIPF₆ has been prepared by the reaction of MnCI₂ [15]aneN₅.3HPF₆, and NaOH in water ([15]aneN₅ is 1,4,7,10,13-pentaazacyclopentadecane). The complex is obtained as a white solid formulated as [Mn(C₁₀H₂₅N₅)Cl](PF₆).3/2H₂O. It is a 2: 1 electrolyte in H₂O and a 1:1 electrolyte in CH₃CN, The complex contains high spin Mn(II), μ_eff = 5.83 B.M., and the EPR spectrum of the polycrystalline solid is indicative of rhombic symmetry at the metal site. The proton NMR relaxation enhancement of aqueous solvent by the complex is 2.3 mM^?1S ^?1 at 24 MHz and 25°C and is indicative of one rapidly exchanging water molecule in the coordination sphere of the solvated complex. The stability constant for the formation of the complex in aqueous solution as measured by potentiometric titration (IogK = 10.7) is four orders of magnitude greater than the comparable linear polyamine. In all, the characterization data are consistent with Mn(lI) strongly bound to a distorted or folded ligand and able to accommodate only one additional ligand.     

Searching for the ionized alkene/aikanol complexes [C2H4+⋅/HOCH3] and [C2H4+⋅/HOCH2CH3]

Experiments on a variety of isomeric [C₃H₈O]⁺? and [C₄H₁₀O]⁺? ions have failed to produce direct evidence for the involvement of the complex ions [C₂H₄⁺?/HOCH₃] and [C₂H₄⁺?/HOC₂H₅]. For the isomers studied, the rearrangements prior to their dissociation of lowest energy requirement (loss of H₂O and C₂H₅?, respectively) are proposed to involve distonic and ylid ions.     

Neue Oxonium-Bromochalkogenate(IV) — Darstellung,Struktur und Eigenschaften von [H3O][TeBr5] · 3C4H8O2 und [H3O]2[SeBr6]

New Oxonium Bromochalcogenates(IV) — Synthesis, Structure, and Properties of [H₃O][TeBr₅] · 3 C₄H₈O₂ and [H₃O]₂[SeBr₆] Dark red crystals of the composition [H₃O][TeBr₅] · 3 C₄H₈O₂ ( 1 ) were isolated from a saturated solution of TeBr₄ in 1,4-dioxane containing a small amount of water. In this compound (space group P2₁/m, a = 8.922(4) Å, b = 13.204(7) Å, c = 9.853(5) Å, β = 91.82(4)° at 150 K) a square pyramidal [TeBr₅]^? anion has been isolated for the first time. The coordination sphere of the anion is completed to a distorted octahedron by weak interaction with a dioxane molecule of the cationic system. The [H₃O]⁺ cations are connected to chains by dioxane molecules. At room temperature the compound is stable only in its mother liquor. Crystalline [H₃O]₂[SeBr₆] ( 2 ) (space group Fm3m, a = 10.421(1) Å at 170 K) is a bromoselenous acid of high symmetry. The [H₃O]⁺ ion is only weakly coordinated by Br atoms of the anion. The anions are isolated octahedral [SeBr₆]^2? units. The structure is isotypic to the K₂[PtCl₆] structure. Despite being a halogenochalcogen(IV) acid, 2 exhibits a remarkable thermal stability. Both oxonium compounds were characterized by single-crystal X-ray structure analyses. Vibrational spectra of 2 are reported.     

Study of the electron transfer reaction between [Co(EDTA)]− and [Ru(NH3)5py]2+ in methanol–water mixtures

The title reaction was studied in different water–cosolvent (methanol) mixtures. The results have been rationalized employing the Marcus–Hush treatment. To apply this treatment, the true, unimolecular, electron‐transfer rate constants (k_et) were obtained from the experimentally measured rate constants after calculation of the equilibrium constant for the processes of formation of the encounter complex. This calculation was carried out using Eigen–Fuoss (EF) and exponential mean spherical (EMSA) approaches employing effective values of the solvent dielectric constant. These effective values were obtained from the measured association constants corresponding to other ion pairs. The results reveal that in these media there is an additional component of reorganization energy, absent in neat solvents. An explanation of the origin of this component is given. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 658–666, 2009     

Synthese und Bau von (4-Picolinium)2[LnCl4(H2O)3]Cl (Ln = Eu,Ho)

Preparation and Structure of (4-Picolinium)₂[LnCl₄(H₂O)₃]Cl (Ln = Eu, Ho) The complex water containing chlorides (4-Picolinium)₂[LnCl₄(H₂O)₃]Cl (Ln = Eu, Ho) were prepared for the first time. The crystal structures were determined on single crystals by X-ray methods. The isotypic compounds crystallize with triclinic symmetry, space group P–1, Z = 2. Surprisingly the structures contain the complex anions [LnCl₄(H₂O)₃]^? (Ln = Eu, Ho) where the ligands form a distorted pentagonal bipyramid, which to our knowledge has not been observed in lanthanide compounds till now.     

Zur Chemie des Kanemits [NaHSi2O5 · 3 H2O]x

On the Chemistry of Kanemite [NaHSi₂O₅ · 3 H₂O]_x Starting from δ-Na₂Si₂O₅ Kanemit was prepared by a direct exchange of Na⁺ by H⁺ in water containing reaction mixtures. By ²⁹Si-, ²³Na- and ¹H-MAS-NMR investigations Kanemit was characterized as a layersilicate [NaHSi₂O₅ · 3 H₂O]. By thermal treatment as well as by dehydration at room temperature under vacuum conditions a monohydrate is formed in which the layerstructure remains nearly unchanged. At temperatures between 100 and 110°C under normal conditions a hydrate phase of the composition [NaHSi₂O₅ · 0.25 H₂O]_x is prepared in which a changed silicate-layerstructure exists.     

Study of the [Cr(H2O)5NO]2+ Complex via Density Functional Theory

On the basis of density functional theory, the spin ground state of chromium‐nitrosyl complex [Cr(H₂O)₅NO]²⁺ (S = 1/2) is studied via B3LYP hybrid method. Its vibrational frequencies, atomic charges, and spin densities are analyzed. The excitation energies are evaluated using the CIS method. Our calculated N‐O stretching frequency and excitation energies are in good agreement with the IR and UV‐vis data. The related Cr^I(H₂O)₆⁺, Cr^II(H₂O)₆²⁺, and Cr^III(H₂O)₆³⁺ complexes are employed as the reference compounds to determine the characteristics of the central Cr. Results indicate that the effective Cr oxidation state is close to Cr(I).     

Co(en)3[B4O5(OH)4]Cl·3H2O和[Ni(en)3][B5O6(OH)4]2·2H2O的合成、结构以及热力学性质

利用水热法合成了两种过渡金属配合物为模板剂的含水硼酸盐晶体Co(en)3[B4O5(OH)4]Cl·3H2O(1) 和 [Ni(en)3][B5O6(OH)4]2·2H2O (2),并通过元素分析、X射线单晶衍射、红外光谱及热重分析对其进行了表征。化合物1晶体结构的主要特点是在所有组成Co(en)33+, [B4O5(OH)4]2–, Cl– 和 H2O之间通过O–H…O、O–H…Cl、N–H…Cl和N–H…O四种氢键连接形成网状超分子结构。化合物2晶体结构的特点是[B5O6(OH)4]–阴离子通过O–H…O氢键连接形成沿a方向有较大通道的三维超分子骨架,模板剂[Ni(en)3]2+阳离子和结晶水分子填充在通道中。     

Double complexes [Co(NH3)5(H2O)]2[Zr3F18]·6H2O and [Co(NH3)6]2[Zr3F18]·6H2O

The structures of orthorhombic bis[pentaammineaquacobalt(III)] tetra‐μ₂‐fluorido‐tetradecafluoridotrizirconium(IV) hexahydrate (space group Ibam), [Co(NH₃)₅(H₂O)]₂[Zr₃F₁₈]·6H₂O, (I), and bis[hexaamminecobalt(III)] tetra‐μ₂‐fluorido‐tetradecafluoridotrizirconium(IV) hexahydrate (space group Pnna), [Co(NH₃)₆]₂[Zr₃F₁₈]·6H₂O, (II), consist of complex [Co(NH₃)_x(H₂O)_y]³⁺ cations with either m [in (I)] or and 2 [in (II)] symmetry, [Zr₃F₁₈]⁶⁻ anionic chains located on sites with 222 [in (I)] or 2 [in (II)] symmetry, and water molecules.