Kinetics of ammoniation of some halobis(ethylenediamine)-rhodium(III) perchlorates in liquid ammonia

Summary The ammoniation ofcis-[Rh(en)₂Cl₂] · (ClO₄) in liquid NH₃ was studied at constant ionic medium of 0.20 m perchlorate in the 0 to 35° range. The complex reacts in two distinct steps to givecis-[Rh(en)₂(NH₃)₂] · (ClO₄)₃, with the intermediate formation ofcis-[Rh(en)₂(NH₃)Cl] · (ClO₄)₂. Both steps follow a conjugate-base mechanism. Activation parameters were obtained for the acid-base preequilibrium and the rate-determining step. The entropies of activation for the rate-determining step are 0 and –42 JK^–1mol^–1 for the first and second ammoniations respectively. These values are considerably lower than those found for the cobalt(III) analogues. The entropy changes for the acid-base equilibria are –84 and –36 JK^–1mol^–1 respectively, which is less negative than those values found for the cobalt(III) analogues. Trans-[Rh(en)₂I₂] · (ClO₄) ammoniates totrans-[Rh(en)₂(NH₃)I] · (ClO₄)₂. The contribution of spontaneous ammoniation to the overall reaction oftrans-[Rh(en)₂I₂] · (ClO₄) is negligible, so the uniqueness oftrans-[Co(en)₂Cl₂] · (ClO₄) among cobalt(III) complexes in this respect is not reproduced for thetrans-dihalotetraamine structure in rhodium(III) complexes. A comparison of cobalt(III) and rhodium(III) amines with respect to activation parameters and the influence of formal charge of the metal complex on reactivity indicates a more associative type of activation for rhodium(III).     

The reactivity of N-2-(4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxo-pyrimidinyl)-L-histidine towards silver(I) and zinc(II) ions

Reactions of N-2-(4-amino-1,6-dihydro-1-methyl-5-nitroso-6-oxopyrimidinyl)-L-histidine with Ag^I and Zn^II ions in 1/1 and 4/1 ligand-to-metal molar ratios, in aqueous media at 25 °C and 0.1 M KNO₃ and KCl ionic strength, respectively, were followed by potentiometric techniques in order to determine formation equilibria for the complex species. The spectral curves, as a function of ligand-to-metal molar ratio at established pH values, were studied and four solid phases of stoichiometry: AgL·4H₂O, Ag(HL)NO₃·1.5H₂O, AgL(OH)₂K₂·H₂O and Zn(HL)₂Cl₂·7H₂O were isolated and characterised by analytical, spectroscopic and thermal measurements.     

Studies on clathrasils VIII. Nonasils-[4158], 88SiO2 · 8M8 · 8M9 · 4M20: Synthesis,thermal properties,and crystal structure

Nonasils-[4¹5⁸], 88SiO₂·8M⁸·8M⁹·4M²⁰, have been synthesized with 2-methylpyrrolidine, hexamethyleneimine, 2-(aminomethyl)-tetrahydrofuran, 1,2-diaminocyclohexane, 2-methylpiperidine, 2-methylpiperazine, 1-aminobutane, 2-aminobutane, and 2-aminopentane as guest molecules, M²⁰. The samples have been prepared from aqueous silicate solutions which were sealed in silica tubes and heated at about 200°C for several weeks. These clathrasils crystallize in space groupFmmm. For the nonasil with 2-aminopentane as the guest molecule and the unit cell dimensionsa _o=22.232(6) Å,b ₀=15.058(4) Å, andc _o=13.627(4) Å, the structure has been refined using 550 non-equivalent single crystal reflexions to a reliability factorR _w =0.125. The 3-dimensional 4-connected silica host framework has three types of cage-like voids, [5⁴6⁴], [4¹5⁸], and [5⁸6¹²], the latter housing the structure-controlling guest molecules, M²⁰. The non-spherical shape of the guest molecules is the most important factor for the formation of nonasils-[4¹5⁸]. On heating nonasils-[4¹5⁸] up to 950°C the organic guest species are driven out and the pure silica form of nonasil is obtained.Part of this study was presented at the 24th Jahrestagung der AGKr, Cologne, 1985 [1]. For part VII see [4].     

Ab initio quantum-chemical calculations of interactions of ions and hydrides of alkali metals with C3H6 and C4H8 molecules

Calculations of the C₃H₆ · LiH, C₄H₈ · M⁺, and C₄H₈ · MH systems and of C₂H₂ · MH complexes (M = Li or Na) were carried out by the unrestricted Hartree-Fock-Roothaan (UHF) method with partial optimization of the geometry using fixed geometric parameters of the C₃H₆ and C₄H₈ molecules. The standard 3-21G and 6-31G* basis sets were used. Unlike the C₃H₆ · LiH structure, the C₄H₈ · M⁺ and C₄H₈ · MH systems are typical complexes. It was found that the C₄H₈ · M⁺, C₄H₈ · MH, and C₂H₂ · MH complexes are similar in coordination of M⁺ ions and MH molecules by carbon atoms in spite of considerable differences in the interatomic distances (–1 A) between these atoms in the C₄H₈ and C₂H₂ molecules. The heats of formation (Q), which were calculated in the UHF/6-31G* approximation and using second- and fourth-order Möller-Plesset perturbation theory taking into account the electron correlation energy in the MP2/6-31G*. MP4(SDQ)/6-31G*, and MP4(SDTQ)/6-31G* approximations, satisfy the following relationships: Q(C₂H₃ · MH) < Q(C₄H₈ · MH) < Q(C₄H₈ · M⁺). It was observed that in going from Li to Na the corresponding values of Q tend to decrease.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 7, pp. 1636–1640, July, 1996.     

Solid state synthesis and characterization of a triple chain calcium(II) coordination polymer showing two different bridging 4-nitrobenzoate coordination modes

The solid state reaction of [Ca(H₂O)₄(η¹-4-nba)(η²-4-nba)] 1 (4-nba = 4-nitrobenzoate) with 2-methylimidazole (L²) at 100 °C results in the formation of a Ca(II) coordination polymer [Ca(H₂O)(L²)(4-nba)₂]_n2. Compound 2 was characterized by elemental analysis, spectral and thermal methods, and its structure determined. The coordination polymer 2 crystallizes in the centrosymmetric monoclinic space group P2₁/n with all atoms situated in general positions and its structure consists of a central Ca(II), a monodentate 2-methylimidazole, a bridging water ligand (μ₂-H₂O), a bidentate bridging (μ₂-η¹:η¹) 4-nba ligand and a monoatomic bridging (μ₂-η²) 4-nba ligand. Each seven-fold coordinated Ca(II) in the title compound is bonded to a nitrogen atom of a terminal 2-methylimidazole (L²) ligand, two symmetry related water molecules and four symmetry related 4-nba ligands, resulting in a distorted pentagonal bipyramidal {CaO₆N} polyhedron. Due to the bridging nature of the aqua and 4-nba ligands [(2-methylimidazole)calcium(II)] units in 2 are linked into a one-dimensional coordination polymer consisting of three chains, all of which propagate along b-axis. In the triple chain coordination polymer a Ca···Ca separation of 3.8432(3) Å is observed between neighbouring Ca(II) ions. The oxygen atoms of the carboxylate and nitro functionalities of the 4-nba ligand and the coordinated water are involved in O–H···O, N–H···O and C–H···O interactions. A comparative study of nine alkaline-earth 4-nitrobenzoate compounds is described.     

Extrahierte Verbindungen von Gallium, Indium und Thallium in Verteilungssystemen mit Tributylphosphat, Cyclohexanon und Isobutylmethylketon

Zusammenfassung Das Verteilungsverhalten der Halogenide und Halogenometallate von Gallium, Indium und Thallium mit den drei Solventien (S) Tributylphosphat (TBP), Cyclohexanon (Cyclo) und Isobutylmethylketon (IBMK) wurde untersucht. Die extrahierten Verbindungen wurden nach der Geradenmethode nach Asmus, der logarithmischen Methode nach McKay, der Methode der kontinuierlichen Variation, durch Analyse der beiden Phasen und durch konduktometrische Extraktionstitration nachgewiesen. Identifiziert wurden folgende Verbindungen: [GaCl₄]^–·2 S, Ga-(SCN) ₃·3 TBP, [Ga(SCN)₄]^–·2 TBP, [InCl₄]^–·2 TBP, [InBr₄]^–·2TBP, [InBr₄]·x Cyclo, [InBr₄]^–·x IBMK, [InJ₄]^–·2 S, In(SCN)₃·3 TBP, [In(SCN)₄]^–·2 TBP, TlCl₃·1 TBP, [TlCl₄]^–·2 S, TlBr₃·1 TBP, [Tl-Br₄] ^–·2 S, TlJ₃·x TBP und [TlJ₄]^–·xS. Wegen der nicht eindeutig definierten Oxydationsstufe von Thalliumjodiden ergaben sich bei den Versuchen experimentelle Schwierigkeiten. Daher wurde in diesem System zusätzlich das radioaktive Isotop ²⁰⁴Thallium verwendet.

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Extracted compounds of gallium, indium and thallium in distribution systems with tributyl phosphate, cyclohexanone and isobutylmethylketone

The behaviour of distribution of the halides and halogenometallates of gallium, indium and thallium with the three solvents (S) tributylphosphate (TBP), cyclohexanone (Cyclo) and isobutylmethylketone (IBMK) are investigated. The extracted compounds are detected with the straight-line method of Asmus, the logarithmic method of McKay, the method of continuous variation, by analysis of the two phases, and with the conductometric extraction-titration. The following compounds were identified: [GaCl₄]^–·2S, Ga(SCN)₃·3TBP, [Ga(SCN)₄]^–·2TBP, [InCl₄]^–·2TBP, [InBr₄]^–·2TBP, [InBr₄]·x Cyclo, [InBr₄]^–·x IBMK, [InJ₄]^– ·2S, In(SCN)₃·3TBP, [In(SCN)₄]^–·2TBP, TlCl₃·1TBP, [TlCl₄]^–·2S, TlBr₃ ·1TBP, [TlBr₄]^–·2S, TlJ₃·x TBP and [TlJ₄]^–·x S. The not unequivocally defined stage of oxidation of thallium iodides resulted in experimental difficulties. Thus, in this system the radioactive isotope ²⁰⁴thallium was additionally used.

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Herrn Professor Dr. E. Asmus zum 60. Geburtstag gewidmet.

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Wie danken Herrn Priv.-Doz. Dr. H. Nickel für die freundliche Unterstützung bei den in der KFA Jülich durchgeführten radioaktiven Messungen.     

Pulse-radiolysis studies of nimesulide in aqueous solution: effect of microheterogeneous media

Nimesulide, a non-steroidal anti-inflammatory drug, forms semi-oxidized species (_max = 350 nm) on reaction with N·₃ and CCl₃OO· in aqueous solution. Their oxidizing nature is confirmed by their ability to undergo an electron-transfer reaction with ABTS^2-, the rate constant for the reaction k = 4.7 × 10⁹ dm³ mol^-1 s^-1. ·OH-adduct constitutes about 94% of the species formed on reaction with ·OH radicals, the remaining 5-6% species are oxidizing in nature. The rate constant for the formation of ·OH-adduct, i.e. k(·OH + Nim-NO₂) = 2.8 × 10¹⁰ dm³ mol^-1 s^-1. Oxygen adds to both e^- _aq and ·OH-adducts of nimesulide with rate constants of 9.5 × 10⁶ dm³ mol^-1 s^-1 and 1.4 × 10⁷ dm³ mol^-1 s^-1, respectively. In the presence of cyclodextrins the nature of the transient species formed is much the same. Binding constants of the drug with CDs are generally quite low in comparison to BSA and range between 37 and 390 dm³ mol^-1. Hydrated electrons add on to nimesulide at the nitro group forming a semi-reduced species with _max = 320 and 500 nm. The rate constant k for this reaction is 1.4 × 10¹⁰ dm³ mol^-1 s^-1. The transient species formed on reaction of e^- _aq or (CH₃)·₂COH radicals with nimesulide seem to be identical, as is seen from their decay rates. The reduction potential of nimesulide for the couple (Nim-NO₂/Nim-NO·₂ ^-) is found to be -0.52 V vs. NHE at pH 7, by cyclic voltammetric and pulse radiolysis techniques.     

Heterometallic copper-lanthanum complexes of 4-(1H)-pyridone

Summary Reaction of Cu(OAc)₂, 4-(1H)-pyridone (LH) and Dy or Gd nitrate in MeOH resulted in the formation of the heterometallic complexes [Cu₂LnL₂(LH)₂(NO₃)(OH)₄· xH₂O], Ln = Dy (1) or Gd (2). Reaction of Cu(OH)₂ with 4-(1H)-pyridone and Dy(NO₃)₃ in DMF resulted in the formation of the heterometallic compound [Cu₂DyL₂(LH)₂(NO₃)₂(OH)₃·DMF] (3). The Cu complexes [Cu(OAc)L]₂ and [CuL₂·DMF] _x have also been prepared from the reaction of 4-(1H)-pyridone with Cu²⁺ in MeOH and DMF, respectively. All the complexes were characterized by elemental analyses, and i.r. and X-band e.s.r. spectroscopies.     

A study of chromic oxide decomposition in an RF argon plasma

Vapor-phase thermal decomposition of chromic oxide in an rf argon plasma was studied using a new experimental system. Homogeneous and heterogeneous modes of reaction were compared, the overall process efficiency being substantially higher for the process carried out entirely in the vapor phase. Reaction products were collected along the reactor wall and studied by chemical methods as well as SEM, X-ray, and IR absorption. The collected powder was highly reactive, fine-grained, and of semiamorphous nature, the average particle size being well below 100 nm. Temperature profiles recorded below the coupling coil by spectroscopic methods were typical of an rf plasma, showing maxima slightly exceeding 5000 K, with the presence of off-axis peaks. Local Cr contents and concentration ratio (Cr)/(Cr₂O₃) in the plasma were determined from the deposition data obtained. A diffusion process was assumed for the wall-deposit buildup. The results obtained confirmed the advantages of using plasma vapor-phase systems, these being higher-efficiency processes and more reliable models than those obtained in the case of gas-solid plasma reactors, where solid particles are injected into the plasma. The thermal decomposition conversion of Cr₂O₃ into Cr was about 8 times higher in the homogeneous gas phase than in the plasma solid phase, all other conditions being equal.Nomenclature c velocity of light, cm × s^–1 - C _Cr ^m metallic Cr content, % by wt. - C _Cr ^t total Cr content, % by wt. - D species diffusivity, cm² · s^–1 - E energy of excited level, eV - f oscillator strength - F rate of species deposition, mol · cm^–2 · s^–1 - g statistical weight - h Planck's constant, J · s^–1 - I radial emission intensity for a given spectral line at a given radius in the plasma, W · sr^–1 · cm^–3 - k Boltzmann's constant, J · K^–1 - l length of collected deposit, cm - m mass of collected deposit, g - M molar weight of Cr - M _Ar ^a molar flow of axial argon, mmol · s^–1 - M _Ar ^p molar flow of peripheral argon, mmol · s^–1 - M _{Cr 2}O₃ molar flow of evaporated Cr₂O₃, mmol · s^–1 - Cr(I) concentration, cm^–3 - Q _T partition function at temperatureT - r reaction radius, cm - R radius of quartz tube, cm - t duration of deposition, s - T temperature, K - total extent of Cr₂O₃ decomposition into Cr, % - Z position of a plane normal to the plasma axis downward the lower turn of rf coil, cm Greek Letters molar ratio of Cr and Cr₂O₃ in deposit - wavelength, nm - species concentration, mol · cm^–3     

Role of Intermolecular Interactions in Formation of Linear Polynuclear Platinum Complexes

The electronic and steric structures of cis- and trans-[Pt(NH₃)₂Hlg₂] were calculated by HF and DFT methods, and the differences between their thermodynamic functions H ⁰ 298, S ⁰ 298, G ⁰ 298, and C _4p = f(T) were evaluated on the basis of DFT force fields. The differences between the stabilities of the cis and trans isomers are mainly due to features of molecular structure, namely, to the energy of interligand interaction. The nonvalent interactions Pt···Pt and NH₂-H···Hlg between the mononuclear fragments cis-[Pt(NH₃)₂· Hlg₂], weakening in the order Cl^- > Br^- > I^-, considerably enhance the stability of the cis isomers and provide conditions for formation of linear polynuclear complexes with Pt-Pt bonds.     

Quenching excited triplet C60 fullerene by tetracyanoethylene in benzonitrile

Quenching excited triplet³C₆₀ fullerene by tetracyanoethylene (TCNE) in a benzonitrile solution proceeds with a rate constant equal to (4.2±0.3) · 10¹⁸ (M · s)^–1. The formation of a radical ion pair [C₆₀ ⁺ · · · TCNE^–] was observed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1228–1230, July, 1993.     

Kinetic and EPR studies on radical polymerization. Radical polymerization of di-2[2-(2-methoxyethoxy)ethoxy]ethyl itaconate

The polymerization of di-2[2-(2-methoxyethoxy)ethoxy]ethyl itaconate (1) with dimethyl 2,2-azobisisobutyrate (2) was studied, in benzene, kinetically and spectroscopically with the electron paramagnetic resonance (EPR) method. The polymerization rate (R _p) at 50°C is given by the equation:R _p=k[2]^0.48 [1]^2.4. The overall activation energy of polymerization was calculated to be 34 kJ·mol^–1. From an EPR study, the polymerization system was found to involve EPR-observable propagating polymer radicals of 1 under the actual polymerization conditions. Using the polymer radical concentration, the rate constants of propagation (k _p) and termination (k _t) were determined. With increasing monomer concentration,k _p(1.54.3 L·mol^–1·s^–1 at 50°C) increases andk _t (1.0·10⁴4.2·10⁴ L·mol^–1·s^–1 at 50°C) decreases, which seems responsible for the high dependence ofR _p on the monomer concentration. The activation energies of propagation and termination were calculated to be 11 kJ·mol^–1 and 84 kJ·mol^–1, respectively. For the copolymerization of 1(M ₁) and styrene (M ₂) at 50°C in benzene the following copolymerization parameters were found:r ₁=0.2,r ₂=0.53, Q₁=0.57, ande ₁=+0.7.     

Specific refractive index increments of copolyamides

Summary The dependence of specific refractive index increments (dñ/dc) of aromatic-aliphatic copolyamides on weight-average molecular weight, temperature and refractive indices of the solvents has been investigated at a wavelength of 546 run. Values of (dñ/dc) increase with increasing molecular weight and temperature. The temperature coefficient of (dñ/dc) in N,N-dimethylacetamide, dichloroacetic acid, trifluoroacetic acid and H₂SO₄ was found to be 7.85 · 10^–4, 5.42 · 10^–4, 6.00 · 10^–4 and 6.83 · 10^–4 cc · g^–1 °C respectively which agrees closely with the values calculated on the basis ofGladstone andDale equation. (dñ/dc) was found to be a linear function of the refractive indices of the solvents.With 3 figures     

Extraction and separation of uranium(VI) and protactinium(V) with 1-(4-tolyl)-2-methyl-3-hydroxy-4-pyridone

Summary The extraction of uranium(VI) from aqueous hydrochloric or nitric acid, and the extraction of protactinium from hydrochloric acid by 1-(4-tolyl)-2-methyl-3-hydroxy-4-pyridone (HY) dissolved in chloroform has been studied. At pH >4, uranium (VI) is quantitatively extracted while at pH < 1 practically all the uranium remains in the aqueous phase. At hydrochloric acid concentrations lower than 1M, protactinium(V) is quantitatively extracted while at hydrochloric acid concentration higher than 5M practically all the protactinium remains in the aqueous phase. This difference in extraction of uranium and protactinium was utilized for their separation. From 0.5M hydrochloric acid, protactinium is quantitatively extracted, and separated from uranium.The composition of the extracted uranium(VI) and protactinium (V) complexes was studied. A uranium complex with the formula UO₂Y₂ · HY was isolated from the chloroform solution. The solution of this complex in chloroform has a maximum absorbance at 319 nm and the molar absorptivity is 3.1×10⁴ l · mole^–1 · cm^–1. Owing to this property uranium can be determined spectro-photometrically directly in the organic phase.

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Zusammenfassung Die Extraktion von Uran(VI) aus wäßriger Salzsäure oder Salpetersäure sowie die Extraktion von Protaktinium aus Salzsäure mit 1-(4-Tolyl)-2-methyl-3-hydroxy-4-pyridon (HY) in chloroformischer Lösung wurde untersucht. Bei pH > 4 wird U(VI) quantitativ extrahiert, während bei pH < 1 praktisch alles Uran in der wäßrigen Phase bleibt. Bei Salzsäurekonzen-trationen unter 1-m wird Protaktinium (V) quantitativ extrahiert, während bei Salzsäurekonzentrationen über 5-m praktisch alles Pa in der wäßrigen Phase bleibt. Dieser Unterschied bei der Extraktion der beiden Elemente wurde für deren Trennung benützt. Pa wird aus 0,5-m Salzsäure quantitativ extrahiert und so von Uran getrennt.Die Zusammensetzung der extrahierten U (VI)- und Pa (V)-Komplexe wurde untersucht. Ein Urankomplex der Formel UO₂ · Y₂ · HY wurde aus der Chloroformlösung isoliert. Die Lösung dieses Komplexes in Chloroform hat ein Absorptionsmaximum bei 319 nm und eine molare Extinktion von 3,1 · 10⁴ l · mol^–1 · cm^–1. Auf Grund dieser Eigenschaft kann Uran spektrophotometrisch direkt in der organischen Phase bestimmt werden.

     

Electron transfer in the photochemical reactions of phenothiazine with halomethanes

Photochemical transformations of phenothiazine (PTA) in solutions of halomethanes CH_nX_4–n (X = Cl, Br; n = 0, 1, 2) and in n-hexane—CH_nX_4–n mixtures under the irradiation with = 337 and 365 nm were studied. The rate constants of quenching of PTA fluorescence with halomethanes (k _q) are 4·10⁵—1.3·10¹⁰ L mol^–1 s^–1. The process occurs due to electron transfer with the C—X bond cleavage in the radical anion fragment of the primary radical ion pair. This results in the formation of the stable radical cation salt (PTA^·+X^–). The plot of k _q vs. free energy of electron transfer corresponds to the Rehm—Weller empirical equation for a one-electron process and is satisfactorily described in terms of the theory of nonradiative electron transitions in the approximation of one quantum vibration.     

Cationic polymerization of hydrocarbon monomers under the action of acyl halide complexes with Lewis acids

Polymerization of isobutylene in hexane at –78 °C under the action of the complex AcBr · 2AlBr₃ (Ac-2) affords polyisobutylene having C=O groups at the head and C-Br or C=C groups at the tail of all the molecules. The presence of the latter indicates that there occurs proton elimination from the growing carbocation with the formation of a superacid HBr · 2AlBr₃ which is unable to initiate the polymerization repeatedly under given contitions. This makes it possible to consider proton elimination as the reaction of the decay of active centers with the rate constantk _d. This value has been calculated from the rate of accumulation of the polymeric molecules having terminal C=C bonds:k _d=3.5 · 10^–4 s^–1. The rate constant of chain growthk _g has been determined from polymerization kinetics and from the content of active centers:k _g=6.2 L mol^–1 s^–1.For part 3, see ref. 4.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 883–886, May, 1993.     

Crystal Structures of 1,5,9,18,22,26-Hexaaza[11.11]-p-cyclophane Adducts; Two-dimensional Supramolecular Networks

Two newly identified supramolecular structures arise from self-assembly of the macrocyclic 1,5,9,18,22,26- hexaaza[11.11]-p-cyclophane salts with o-nitrophenol (C₂₈H₅₀N₆)⁴⁺·4(C₆H₄NO₂O)⁻ (1) and with HCl (C₂₈H₅₂N₆)⁶⁺·6Cl^-·4H₂O (2). In both cases two-dimensional supramolecular sheets are formed.     

Der Einfluß großer Salzkonzentrationen auf die Oxydationsreaktion von Fe(phen) 3 2+ mit Ce(IV) in Schwefelsäure

The influence of NaClO₄, NaCl and Na₂SO₄ on the oxidation of Fe(phen) ₃ ²⁺ by Ce(IV) was investigated by means of the stopped-flow method. At the concentrations range of NaClO₄ and NaCl 0.1–1.0M the rate constant values decrease from 1.03·10⁵ to 0.56·10⁵M^–1s^–1 and from 1.08·10⁵ to 0.81·10⁵M^–1s^–1 respectively.In varying concentrations of Na₂SO₄ solutions (0.05–0.35M) the rate constant values decrease from 1.05·10⁵M^–1s^–1 to 0.45·10⁵M^–1s^–1.Taking into account the negative salt effect the mechanism of the reaction progress is proposed.

     

Modeling of iron adsorption on HTTA-loaded polyurethane foam using Freundlich,Langmuir and D-R isotherm expressions

The sorption of Fe(III) at low pH range from 1 to 4.5 on open cell polyether type HTTA-loaded polyurethane foam has been carried out using batch technique. The optimum shaking time for 2.5· 10^–4M solution of Fe(III) was found to be 30 minutes. The concept of macropore and micropore nature of polyurethane foam sorbent offers unique advantages of adsorption. Freundlich and Langmuir adsorption isotherms are followed at low concentration range from 1·10^–4 to 3·10^–4M solution of Fe(III). The Freundlich constant (1/n=0.46±0.013 andK=9.16±1.39 mg·g^–1) and Langmuir isotherm constants(M=21.78 mg·g^–1 andb=88.41±9.731·g^–1) were established. The sorption mean free energyE=12.22±0.09 kJ·mol^–1 and loading capacityC _m =145.21±6.1 mg·g^–1 were evaluated using Dubinin-Radushkevich isotherm, which suggested that the adsorption mechanism was chemisorption.     

Evidence of 13 hybrid fluoroaluminates in the composition space diagram of the Al(OH)3–tren–HF–ethanol system

Thirteen phases are now evidenced in the composition space diagram of the Al(OH)₃–tren–HF–ethanol system at 190 °C. Solvothermal syntheses are performed under microwave heating. Six new organic–inorganic fluorides crystallise and their structures are determined: (H₃O)·[H₄tren]₂·(AlF₆)₃·6H₂O (P-1, Z = 2), [H₃tren]₂·(AlF₅(H₂O))₃·8H₂O (C2/c, Z = 8), [H₃tren]₄·(AlF₆)₂·(Al₂F₁₁)·(F)·10H₂O (P2₁/n, Z = 2), [H₃tren]₂·(Al₄F₁₈)·3.5H₂O (P6₃, Z = 2), [H₃tren]₂·(Al₄F₁₈) (P-1, Z = 1), and [H₃tren]₄·(Al₈F₃₅)·(OH)·H₂O (P-1, Z = 1). The existence domains are approximately located for all phases. Tren amine is tetraprotonated at high HF concentration, otherwise it is triprotonated. A protonated water cluster, H₃O⁺(H₂O)₆, appears in (H₃O)·[H₄tren]₂·(AlF₆)₃·6H₂O while a new Al₄F₁₈ unit, found in [H₃tren]₂·(Al₄F₁₈), is evidenced; it results from corner and edge sharing association of four AlF₆ octahedra. Finally, the structure of [H₃tren]₄·(Al₈F₃₅)·(OH)·H₂O revealed the largest known fluoroaluminate polyanion, built from eight vertex sharing AlF₆ octahedra, (Al₈F₃₅)¹¹⁻.