Solid state mechanism of the thermal dehydration of [Rh(NH3)5(H2O)]X3 (X = Cl−, Br−, I−)

The solid phase thermal deaquation-anation of [Rh(NH₃)₅(H₂O)]X₃ (X = Cl⁻, Br⁻, I⁻) has been investigated by means of isothermal TG measurements applying all the principal g(α) expressions (0.8 ⩾ α ⩾ 0.2). The values found for the activation energy are low: ≈ 95 kJ mol⁻¹ for the Cl⁻ compound; ~105 kJ mol⁻ for the Br⁻ compound and ≈110 kJ mol⁻¹ for the I⁻ compound. These data permit the assignment of the deaquation-anation mechanism of the S_N1 dissociative type, involving a square-based pyramid activated complex and elimination of water as Frenkel defects. These values are similar to those reported for the Co(III) and Ir(III) analogues, indicating that the D_q parameter is not the principal contribution to the activation energy of the dehydration-anation process.     

Syntheses and characterization of Pb(trz) n X2 (X = CH3COO−, NCS−, and n = 1, 2) complexes,and crystal structure of [Pb(trz)2(MeOH)](ClO4)2·H2O

Lead(II) complexes with 2,4,6-tris(2-pyridyl)-1,3,5-triazine (trz) have been synthesized using a direct synthetic method and characterized by IR and ²⁰⁷Pb NMR spectroscopy and CHN elemental analysis. The structure of [Pb(trz)₂(MeOH)](ClO₄)₂·H₂O was confirmed by X-ray crystallography. Single-crystal X-ray data for [Pb(trz)₂(MeOH)](ClO₄)₂·H₂O show the complex to be monomeric with the Pb having an unsymmetrical seven-coordinate geometry, coordinated by six nitrogen atoms of the trz ligands and one oxygen atom of MeOH. The arrangement of the ligands in the [Pb(trz)₂(MeOH)](ClO₄)₂·H₂O complex exhibits a coordination gap around the Pb(II), occupied possibly by a stereoactive lone pair of electrons on lead(II); the coordination around the lead atoms is hemidirected.     

Reactions of CH3SH and CH3SSCH3 with gas-phase hydrated radical anions (H2O)n(•-), CO2(•-)(H2O)n, and O2(•-)(H2O)n

The chemistry of (H(2)O)(n)(?-), CO(2)(?-)(H(2)O)(n), and O(2)(?-)(H(2)O)(n) with small sulfur-containing molecules was studied in the gas phase by Fourier transform ion cyclotron resonance mass spectrometry. With hydrated electrons and hydrated carbon dioxide radical anions, two reactions with relevance for biological radiation damage were observed, cleavage of the disulfide bond of CH(3)SSCH(3) and activation of the thiol group of CH(3)SH. No reactions were observed with CH(3)SCH(3). The hydrated superoxide radical anion, usually viewed as major source of oxidative stress, did not react with any of the compounds. Nanocalorimetry and quantum chemical calculations give a consistent picture of the reaction mechanism. The results indicate that the conversion of e(-) and CO(2)(?-) to O(2)(?-) deactivates highly reactive species and may actually reduce oxidative stress. For reactions of (H(2)O)(n)(?-) with CH(3)SH as well as CO(2)(?-)(H(2)O)(n) with CH(3)SSCH(3), the reaction products in the gas phase are different from those reported in the literature from pulse radiolysis studies. This observation is rationalized with the reduced cage effect in reactions of gas-phase clusters.     

A Novel Three-Dimensional Network Isophthalato-Bridged Lanthanide Complex: {Ln[C6H4(COO−)2-1,3](CH3COO−)(H2O)2}·H2O

The three-dimensional network of lanthanide (III) complexes with isophthalato (IPT) ligand, (Eu[C₆H₄(COO^?)₂-1,3](CH₃COO^?)(H₂O)₂}·H₂O 1 and {Sm[C₆H₄(COO^?)₂-1,3](CH₃COO^?) (H₂O)₂} H₂O 2, has been prepared by the hydro(solvo)thermal reaction of Eu(C1O₄)₃·6H₂O or Sm(C1O₄)₃·6H₂O, 1,3-dicyanobenzene and acetic acid in the presence of ethanol and H₂O. In the reaction, 1,3-dicyanobenzene was hydrolyzed to give IPT ligand. Single crystal x-ray analysis revealed that crystals 1 and 2 are isomorphous with the isostructural {M[C₆H₄(COO^?)₂-1,3](CH₃COO^?)(H₂O)₂}·H₂O unit. In 1 and 2, IPT acts as a bridging ligand to connect three adjacent metal atoms, forming a network like an undulating sheet paralleling the bc plane. The carboxylate from acetate bridges two adjacent metal atoms in a tridentate mode between the different sheets to extend the structure into a three-dimensional network.     

On the thermal decomposition of [Fe2NiO(CH3COO)6(H2O)3]·2H2O

The heteronuclear-oxoacetate with the composition [Fe₂NiO(CH₂COO)₆(H₂O)₃]·2H₂O decomposed on heating, forming nickel ferrite NiFe₂O₄ and (depending on the decomposition conditions) in part other solid phases. H₂O, CH₃COOH, acetone and CO₂ were also formed in the decomposition. A reaction scheme is given for the decomposition. The products were porous powders with grain diameters between 3 and 10m. On increase of the temperature of decomposition from 300 to 800 C, the BET surface area and the surface area of the pores decreased, but only a small alteration in grain size was observed. As a result of thermal treatment in the temperature region abone 800C, larger aggregates of grains were formed in sintering processes.

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Zusammenfassung Heteronukleare-Oxoazetate der Zusammensetzung [Fe₂NiO(CH₃COO)₆(H₂O)₃]·2H₂O werden durch Erhitzen zersetzt, wobei Nickelferrite NiFe₂O₄ und — in AbhÄngigkeit von den Bedingungen der Zersetzung — mit einem Teil anderer fester Phasen gebildet wird. In der Zersetzungsreaktion werden auch H₂O, CH₃COOH, Azeton und CO₂ gebildet. Es wird ein Reaktionsschema für die Zersetzung angegeben. Die Produkte sind poröse Pulver mit einem Korndurchmesser zwischen 3 und 10 m. Wird die Zersetzungstemperatur von 300 auf 800C erhöht, nimmt die BET-OberflÄche und die PorenoberflÄche ab, wobei sich die Korngrö\e aber nur wenig verÄndert. Im Ergebnis der WÄrmebehandlung im Temperaturbereich oberhalb 800C werden durch Sinterprozesse grö\ere Partikelaggregate gebildet.

     

Synthesis and X-ray diffraction study of cs3[UO2(CH3COO)3]2[UO2(CH3COO)(NCS)2(H2O)] and Cs5[UO2(CH3COO)3]3[UO2(NCS)4(H2O)] · 2H2O

Cs₃[UO₂(CH₃COO)₃]₂[UO₂(CH₃COO)(NCS)₂(H₂O)] (I) and Cs₅[UO₂(CH₃COO)₃]₃[UO₂ (NCS)₄(H₂O)] · 2H₂O (II) have been synthesized via the reaction between uranyl acetate and cesium thiocyanate in aqueous solution. According to single-crystal X-ray diffraction data, both compounds crystallize in monoclinic system with the unit cell parameters a = 18.7036(5) Å, b = 16.7787(3) Å, c = 12.9636(3) Å, β = 92.532(1)°, space group C2/c, Z = 4, R = 0.0434 (I); and a = 21.7843(3) Å, b = 24.6436(5) Å, c = 13.1942(2) Å, β = 126.482(1)°, space group Cc, Z = 4, R = 0.0273 (II). Uranium-containing structural units of compound (I) are mononuclear [UO₂(CH₃COO)₃]^? and [UO₂(CH₃COO)(NCS)₂(H₂O)]^? moieties, which correspond to the AB ₃ ⁰¹ and AB⁰¹M ₃ ¹ crystallochemical groups (A = UO ₂ ²⁺ , B⁰¹ = CH₃COO^?, M¹ = NCS^? and H₂O). The structure of compound II is built of [UO₂(CH₃COO)₃]^? and [UO₂(NCS)₄(H₂O)]^2? complexes, which belong to the AB ₃ ⁰¹ and AM ₅ ¹ crystallochemical groups, respectively. Uranium-containing complexes in both structures are linked into a framework by hydrogen bonds and electrostatic interactions with cesium cations. The IR spectra of compounds I and II agree well with X-ray diffraction data.     

The conformational changes of 5SrRNA from lupin seeds in presence of ClO 4 − , NO 3 − , Br−, BF 4 − , SO 4 2− , Cl−, COO− anions by adiabatic scanning calorimetry

The results of calorimetric studies of 5SrRNA solutions isolated from lupin seeds in the pressence of the ClO ₄ ^? , NO ₃ ^? , Br ₄ ^? , SO ₄ ^2? , Cl^?, COO^? (maleic and fumaric acids) anions were reported. The plots of calorimetric curves, enthalpy of conformational changes of two state transitions were presented. Using the deconvolution method proposed by Freire and Biltonen the elementary transitions were distinguished and discussed.     

Catalytic performance of ZnFe2O4 nanoparticles prepared from the [ZnFe2O(CH3COO)6(H2O)3]·2H2O complex under microwave irradiation

Research on Chemical Intermediates - Using the heterometallic oxo-centered trinuclear [ZnFe2O(CH3COO)6(H2O)3]·2H2O complex as a novel precursor, pure and single-phase ZnFe2O4 nanostructure was...     

Vibrational manifestations of strong non-Condon effects in the H3O(+)·X3 (X = Ar, N2, CH4, H2O) complexes: a possible explanation for the intensity in the "association band" in the vibrational spectrum of water

The harmonic approximation provides a powerful approach for interpreting vibrational spectra. In this treatment, the energy and intensity of the 3N- 6 normal modes are calculated using a quadratic expansion of the potential energy and a linear expansion of the dipole moment surfaces, respectively. In reality, transitions are often observed that are not accounted for by this approach (e.g. combination bands, overtones, etc.), and these transitions arise from inherent anharmonicities present in the system. One interesting example occurs in the vibrational spectrum of H(2)O((l)), where a band is observed near 2000 cm(-1) that is commonly referred to as the "association band". This band lies far from the expected bend and stretching modes of the water molecule, and is not recovered at the harmonic level. In a recent study, we identified a band in this spectral region in gas-phase clusters involving atomic and molecular adducts to the H(3)O(+) ion. In the current study we probe the origins of this band through a systematic analysis of the argon-predissociation spectra of H(3)O(+)·X(3) where X = Ar, CH(4), N(2) or H(2)O, with particular attention to the contributions from the non-linearities in the dipole surfaces, often referred to as non-Condon effects. The spectra of the H(3)O(+) clusters all display strong transitions between 1900-2100 cm(-1), and theoretical modeling indicates that they can be assigned to a combination band involving the HOH bend and frustrated rotation of H(3)O(+) in the solvent cage. This transition derives its oscillator strength entirely from strong non-Condon effects, and we discuss its possible relationship to the association band in the spectrum of liquid water.     

Crystal,molecular, and electronic structure of carboxylate [Fe3O(CH3COO)6(H2O)3]NO3·4H2O

Results of X-ray structural analysis, IR spectroscopy, and quantum chemical study of the [Fe₃O(CH₃COO)₆(H₂O)₃]NO₃·4H₂O complex are reported. The crystal belongs to the monoclinic system with a=15.688(3), b=11.767(2), c=15.318(4) Å, γ=92.54(3)^o, space group P2₁/a, R=0.078. The molecule has a trinuclear structure: three iron atoms occupy the vertices of an equilateral, triangle with an Fe−Fe distance of 3.29 Å and are bonded by the μ₃-oxo and μ-CH₃COO⁻ (O,O′) ligands. To each iron atom, one water molecule is coordinated. Using the obtained values of populations on 3d AO of Fe (d _xy ^1.34 ; d _xz ^1.39 ; d _yz ^1.46 ; ; ) and charges on oxygen atoms (O _c ^−0.5 ; O _ac ^−0.31 ; O _w ^−0.31 ), we estimated the values of isomeric shift and quadrupole splitting (0.75 and 0.70 mm/sec, respectively; these are close to the experimental values of 0.75 and 0.58 mm/sec, (300 K)). Institute of Chemistry, Moldovian Academy of Sciences. Moldovian State University. Institute of Applied Physics, Moldovian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii., Vol. 35, No. 2, pp. 112–120, March–April, 1994. Translated by T. Yudanova     

Phase transition in Mg(Ch3COO)2·4X2O (X = H,D) from temperature-dependent vibrational spectra

Two phase transitions at 246 ± and 148 ± 3 K in the titled compound are inferred from the temperature variation of its thermosensitive IR and Raman bands and both of these have been attributed to reorientations of the CH₃ groups.     

Synthesis and structure of (NH4)2[(UO2)2(C2O4)(CH3COO)4] · 2H2O

Single crystals of (NH₄)₂[(UO₂)₂C₂O₄(CH₃COO)₄] · 2H₂O have been synthesized and studied. The compound crystallizes in the orthorhombic system with the unit cell parameters a = 6.9225(14) Å, b = 12.327(3) Å, c = 14.619(3) Å, space group Immm, Z = 2, and V = 1247.6(5) ų. The main structural units of the crystals are the isle binuclear groups [(UO₂)₂C₂O₄(CH₃COO)₄]^2? belonging to the crystal-chemical group A₂K⁰²B ₄ ⁰¹ (A = UO ₂ ²⁺ , K⁰² = C₂O ₄ ^2? , B⁰¹ = CH₃COO^?) of the uranyl complexes. The uranium-containing groups are linked into a three-dimensional framework due to electrostatic interaction with the ammonium cations and through a system of hydrogen bonds involving atoms of the water molecules, oxalate and acetate ions, and ammonium and uranyl cations.     

Synthesis and Structure of Trinuclear Iron Acetate [Fe3O(CH3COO)6(H2O)3][AuCl4]·6H2O

Iron acetate of composition [Fe₃O(CH₃COO)₆(H₂O)₃][AuCl₄]·6H₂O (I) was synthesized and investigated by X-ray diffraction analysis and Mössbauer spectroscopy. The [Fe₃O(CH₃COO)₆(H₂O)₃]⁺ complex cation has a structure typical for ₃-O bridged trinuclear ferric compounds with iron atoms lying at the vertices of a regular triangle with an oxygen atom at the center. The iron atoms are each coordinated by 4 oxygen atoms of the four bridging carboxylic groups, the ₃-O bridging atom, and the coordinated water molecule in the trans-position to the latter. In the trinuclear cation, the Fe(III) ions are coupled by antiferromagnetic exchange interactions with the exchange parameter J = -29.0 cm ^–1 (HDVV model for D _3h symmetry). The specific role of the solvate water molecules in structure formation is discussed.     

The electrochemical behaviour of polycrystalline silver electrodes in Na2CO3 solution and the effect of ClO− 4 ions

The electrochemical behaviour of polycrystalline silver electrodes in Na₂CO₃ solutions was studied under potentiodynamic and potentiostatic conditions and complemented with X-ray diffraction analysis. Potentiodynamic E/i anodic curves exhibit active passive transition prior to an oxygen evolution reaction. The active region involves a small peak AI followed by a major peak AII before the passive region. Peak AI is assigned to the formation of an Ag₂O layer while peak AII is due to the formation of an Ag₂CO₃ layer. The height of the anodic peaks increases with increasing Na₂CO₃ concentration, scan rate and temperature. The effect of increasing additions of NaClO₄ on the electrochemical behaviour of Ag in Na₂CO₃ solutions was investigated. The perchlorate ions stimulate the active dissolution of Ag, presumably as a result of the formation of soluble AgClO₄ salt. In the passive region, ClO⁻ ₄ ions tend to break down the dual passive film, leading to pitting corrosion at a certain critical pitting potential. The pitting potential decreases with ClO⁻ ₄ concentration. Potentiostatic current/time transients showed that the formation of Ag₂O and Ag₂CO₃ layers involves a nucleation and growth mechanism under diffusion control. However, in the presence of ClO⁻ ₄ ions, the incubation time for pit initiation decreases on increasing the anodic potential step. Received: 3 July 1998 / Accepted: 10 March 1999     

Synthesis and Crystal Structure of the Copper Complex {[Cu（CH3COO）2（bbtz）]（H2O）2}n

1 INTRODUCTION The design and synthesis of metal-organic frame- work structures have been extensively studied due to their unexpected properties for potential applications as functional materials as well as the intriguing ar- chitectures and topologies[1～4]. When rigid bifunc- tional ligands are used to connect metal centers, to- pology of the network is usually determined by the coordination geometry of the central metal prefer- ence. Contrary to rigid ligands, the bifunctional fle- xib…     

Studies of the hydrated oxonium radical H3O·(H2O)n and the ammoniated ammonium radical NH4·(NH3)n by neutralized ion beam techniques

Neutralized ion beam studies of the clusters NH₄·(NH₃)_n and H₃O·(H₂O)_n,n = 0–3, and their fully deuterated analogs are presented. Stabilization of the hypervalent monomer radicals is found to accompany solvation. Cluster stability is found to decrease with increasing size. Reasons for this observation are discussed. Internally excited clusters are found to stabilize efficiently through the sequential loss of structural units (NH₃ or H₂O). The mixed isotopic dimer clusters (D₂¹⁸O)·D·(D₂¹⁶O) and (HDO)·D·(D₂O) are also investigated. Presence of the D₃¹⁶O radical structural unit is found to be crucial to dimer stability. This is consistent with the results of earlier investigations involving the monomer which showed the surprising lifetime progression τ(D₃¹⁶O) ≫; τ(D₃¹⁸O) ⩾ τ(H₃¹⁶O).     

The Thermal Decomposition of Fe(NO3)3·9H2O

Using thermogravimetric analyses as well as isothermal gravimetric measurements, the thermal stability of the iron(III) nitrate nanohydrate has been determined. Several decomposition stages are the result of melting, evaporation and hydrolysis processes occurring in the salt—water system in the temperature range of 20–400°C. Some of the intermediates and the final product (-Fe₂O₃) are characterized by means of chemical analyses, X-ray diffraction patterns and IR spectra.This revised version was published online in November 2005 with corrections to the Cover Date.     

Raman intensities of liquids: absolute scattering activities and ClO bond EOPs of ClO−, ClO−2, ClO−3 and ClO−4 ions in aqueous solution

Absolute Raman scattering activities of aqueous solutions of the following ions have been measured: ClO⁻, ClO⁻₂, ClO⁻₃, ClO⁻₄. Electro-optical parameters (EOPs) for the ClO bonds in these compounds were calculated. Equilibrium bond polarizabilities and their derivatives with respect to bond length can be correlated with the number of valence electrons in non-bonding and antibonding orbitals. High equilibrium bond polarizability goes with small polarizability derivatives, and vice versa, for the compounds studied here.     

Temperature dependence of the substrate selectivity in the hydroxylation of alkylbenzenes in the H2O2−H2SO4 system

The substrate selectivity in the hydroxylation of methylbenzenes in the H₂O₂−H₂SO₄ (70 wt.%) system was studied at 15–55 °C. The activation entropy correlates with the basicity of the arenes, while the substrate selectivity and activation enthalpy correspond both with the basicity and ionization potentials of ArH. We concluded that the structure of the reaction transition state is intermediate between a charge transfer complex and σ-complex. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 35, No. 1, pp. 39–43, January–February, 1999.