Molecular,thermodynamic, and kinetic parameters of iodomethanes and iodomethyl radicals: <Emphasis Type="Italic">ab initio</Emphasis> calculations

The wave functions and enthalpies of formation of the ground states of iodomethanes CH_{4– x} I_x and iodomethyl radicals CH_3–x I_x. (x = 1–3) were calculated ab initio with regard to electron correlation. The geometries of the molecules of these compounds were determined, as well as the normal mode frequencies and other parameters, which were used for calculating the thermodynamic functions in the 0–1500 K range. These functions were used for calculating the constants of the CH_4–x I_x CH_4–x I _x–1 + I and CH_4–x I_x + I CH_{4– x} I _x–1 + I₂ equilibria, which, in turn, were used for calculating the corresponding rate constants in the high concentration limit.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1812–1822.Original Russian Text Copyright © 2004 by Dymov, Skorobogatov, Tschuikow-Roux.This revised version was published online in April 2005 with a corrected cover date.     

Silylating Agents Grafted onto Silica Derived from Leached Chrysotile

Silica from leached chrysotile fibers (SILO) was silanized with trialkoxyaminosilanes to yield inorganic–organic hybrids designated SILx (x=1–3). The greatest amounts of the immobilized agents were quantified as 2.14, 1.90, and 2.18 mmol g⁻¹ on SIL1, SIL2, and SIL3 for –(CH₂)₃NH₂,–(CH₂)₃NH(CH₂)₂NH₂, and –(CH₂)₃NH(CH₂)₂NH(CH₂)₂NH₂ groups attached to the inorganic support. The infrared spectra for all modified silicas showed the absence of the Si–OH deformation mode, originally found at 950 cm⁻¹, and the appearance of asymmetric and symmetric C–H stretching bands at 2950 and 2840 cm⁻¹. Other important bands associated with the organic moieties were assigned to ν_as(NH) at 3478 and ν_sym(NH) at 3418 cm⁻¹. The NMR spectrum of the solid precursor material suggested two different kinds of silicon atoms: silanol and siloxane groups, between −90 and 110 ppm; however, additional species of silicon that contain the organic moieties bonded to silicon at −58 and −66 ppm appeared after chemical modification. These modified silicas showed a high adsorption capacity for cobalt and copper cations in aqueous solution, in contrast to the original SILO matrix, confirming the unequivocal anchoring of silylating agents on the silica surface.     

Oxygen States in Oxides with a Perovskite Structure and Their Catalytic Activity in Complete Oxidation Reactions: System La1 – x Ca x FeO3 – y (x = 0–1)

Oxygen states in the La_{1 – x} Ca _x FeO_{3 – y} perovskites prepared using different procedures are studied by temperature-programmed reduction (TPR). Results are compared to data on the catalytic activity in the oxidation of methane and carbon monoxide. The activity of the samples in the CO and CH₄ oxidation over a wide temperature range (200–600°C) is shown to correlate with the amount of reactive surface and subsurface oxygen removable during TPR below 420°C. These oxygen states in the samples of the La_{1 – x} Ca _x FeO_{3 – y} series can be associated with the domain or intergrain boundaries. No correlation is found between the amount of lattice oxygen removable during TPR and the activity of the La_{1 – x} Ca _x FeO_{3 – y} samples in the complete oxidation of methane at temperatures of 450–600°C. It is suggested that catalytic complete oxidation is determined by the most reactive surface and subsurface oxygen states located at the interphase boundaries, whereas the lattice oxygen does not participate in these reactions.     

Excess molar heat capacities and excess molar volumes of some mixtures of propylene carbonate with aromatic hydrocarbons

Excess molar volumes V ^E and excess molar heat capacities C _P ^E at constant pressure have been measured, at 25°C, as a function of composition for the four binary liquid mixtures propylene carbonate (4-methyl-1,3-dioxolan-2-one, C₄H₆O₃; PC) + benzene (C₆H₆;B), + toluene (C₆H₅CH₃;T), + ethylbenzene (C₆H₅C₂H₅;EB), and + p-xylene (p-C₆H₄(CH₃)₂;p-X) using a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. All the excess volumes are negative and noticeably skewed towards the hydrocarbon side: V ^E (cm³-mol^–1) at the minimum ranges from about –0.31 at x₁=0.43 for {x₁C₄H₆O₃+x₂p-C₆H₄(CH₃)₂}, to –0.45 at x₁=0.40 for {x₁C₄H₆O₃+x₂C₆H₅CH₃}. For the systems (PC+T), (PC+EB) and (PC+p-X) the C _P ^E s are all positive and even more skewed. For instance, for (PC+T) the maximum is at x _1,max =0.31 with C _P,max ^E =1.91 J-K^–1-mol^–1. Most interestingly, C _P ^E of {x₁C₄H₆O₃+x₂C₆H₆} exhibits two maxima near the ends of the composition range and a minimum at x _1,min =0.71 with C _P,min ^E =–0.23 J-K^–1-mol^–1. For this type of mixture, it is the first reported case of an M-shaped composition dependence of the excess molar heat capacity at constant pressure.Communicated at the Festsymposium celebrating Dr. Henry V. Kehiaian's 60^th birthday, Clermont-Ferrand, France, 17–18 May 1990.     

Heat capacities and densities of mixtures of very polar substances. 3. Mixtures containing either trichloromethane or 1,4-dioxane or diisopropylether

Excess molar heat capacities C _P ^E at constant pressure and excess molar volumes V ^E have been determined, as a function of mole fraction x₁ at 25°C and atmospheric pressure, for 10 binary liquid mixtures containing either trichloromethane (series I) with C₆H₅CH₃, or C₆H₅Cl, or C₅H₅N, or CH₃COCH₃, or C₆H₅NO₂; 1,4-dioxane (series II) with (C₂H₅)₃N, or (CH₃)₂CHOCH(CH₃)₂, or (CH_{3 2}SO); or diisopropyl ether (di-1-methylethyl ether) (series III) with (C₂H₅)₃N, or CHCl₃. The dipole momentsp (10^–30C-m) of the substances range from nearly 0 to 14.1 for nitrobenzene. The C _P ^E of series I and III are all positive, with C _P ^E (x₁=0.5) (J-K^–1-mol^–1) ranging from 1.04 for {x₁CHCl₃+x₂C₆H₅Cl} to 16.66 for {x₁(CH₃)₂CHOCH(CH₃)₂+x₂CHCl₃}. In series II, the C _P ^E are positive and small for {x₁1,4-C₄H₈O₂+x₂(CH₃)₂CHOCH(CH₃)₂}, S-shaped and small for {x₁1,4-C₄H₈O₂+x₂(C₂H₅)₃N}, and negative and small for {x₁1,4-C₄H₈O₂+x₂(CH₃)₂SO}. The excess volumes are small and positive for {x₁CHCl₃+x₂C₆H₅CH₃}, S-shaped for {x₁CHCl₃+x₂CH₃COCH₃}, {x₁1,4-C₄H₈O₂+x₂(C₂H₅)₃N} and {x₁(CH₃)₂CHOCH(CH₃)₂+x₂(C₂H₅)₃N}, and negative for the other systems.Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday     

Preparation and Electrical Properties of Lnx(SiO4)6O(1.5x?12) (Ln: Nd, La) with Apatite Structure

In this study, Ln_x(SiO₄)₆O_(1.5x–12) (Ln: Nd, La) materials as electrolytes for solid oxide fuel cells (SOFC) were prepared by the sol-gel process. It has been reported that the apatite structure of Ln_x(SiO₄)₆O_(1.5x–12) shows higher ionic conductivity than yttrium-stabilized zirconium oxide at the working temperature of the SOFC. Ln₁₀(SiO₄)₆O₃ is a major component of the Ln_x(SiO₄)₆O_(1.5x–12) system. Ln₁₀(SiO₄)₆O₃ consists of Ln_9.33(SiO₄)₆O₂ and a small amount of Ln₂SiO₅. It has been proposed that the ionic conductivity of Ln_x(SiO₄)₆O_(1.5x–12) decreases with increasing Ln₂SiO₅ with non-apatite structure. The object of the present study was to bring about this decrease by generating Ln₂SiO₅ in the system.Precursor solutions for synthesis of the powder were prepared using tetraethoxysilane (Si(OC₂H₅)₄) and neodymium acetate monohydrate (Nd(CH₃COO)₃·H₂O) or lanthanum acetate monohydrate (La (CH₃COO)₃·H₂O) as raw materials and acetic acid (CH₃COOH), 2-methoxyethanol (C₂H₅OCH₂CH₂OH), and triethanolamine (N(CH₂CH₂OH)₃) as solvents. To obtain the powder, the solution was dried and heat-treated at 600 °C for 2 h. Disks made from the powder were heat-treated at temperatures between 1100 and 1500 °C for 10 h. The results of an XRD investigation indicate that almost all diffraction peaks of these samples could be assigned to Ln_9.33(SiO₄)₆O₂. The sample with x = 10.00 included a small amount of Ln₂SiO₅. The ionic conductivity of this latter sample was higher than that of other samples with similar values of x (x = 9.33 and 10.67).     

Co-hydrolysis products of tetraethoxysilane and methyltriethoxysilane in the presence of tetramethylammonium ions: Part 2 [1]

²⁹Si NMR peaks due to species with the double four-membered ring siloxane backbone composed of both Si(O^–)_4/2 and CH₃Si(O^–)_3/2 units, (CH₃) _n Si₈O _{20 – n} ^{/(8 – n) –} (n=1–3), formed by co-hydrolysis of tetraethoxysilane and methyltriethoxysilane in the presence of tetramethylammonium ions in methanol have been assigned. It has been found that ²⁹Si NMR peaks due to Si(OSi)₃(O^–) units shift to lower frequencies by replacement of the adjacent Si(O^–)_4/2 units by CH₃Si(O^–)_3/2 units, in other words, with increasing m value in Si[OSi(O^–)₃]_{3 – m} [OSi(CH₃) (O^–)₂] _m (O^–) (m=0–2). Peaks from CH₃ Si(OSi)₃ units in the species have also appeared as separated due to the kind of neighbor structural units. On the basis of the assignments, positions of CH₃Si(O^–)_3/2 units in the cubic octameric siloxane framework of (CH₃) _n Si₈O _{20 – n} ^{/(8 – n) –} (n=2, 3), for both of which three isomers are present, have been estimated.     

Photocatalytic Reduction of Nitrate in Water on Meso-Porous Hollandite Catalyst: A New Pathway on Removal of Nitrate in Water

Photocatalysis of a hollandite compound K _x Ga _x Sn_8–x O₁₆ (x = ca. 1.8) was examined for the reduction of nitrate to N₂ with a reducing agent of methanol in water under UV irradiation. Hollandites have a characteristic one-dimensional tunnel structure. The meso-porous hollandite was prepared by sol-gel method. This hollandite was used as the photocatalyst and its reaction process was quantitatively analyzed by using ion chromatograph and on-line mass spectrometry. The hollandite photocatalyst showed a significant activity for the formation of N₂ from NO ₃ ^– . Two factors, an increase in UV intensity and a lowering in pH of the solution, contributed to improvement in the selectivity for N₂. The selectivity for N₂ was improved to reach the perfect level by adjusting the factors. Although, in the previous report, the nitrate was mainly reduced to NH ₄ ⁺ or NO ₂ ^– , the present photocatalytic conditions converted it to N₂. The observed photocatalytic reduction of NO ₃ ^– to N₂ with reducing agent CH₃OH was conjugated to the partial oxidation of CH₃OH to HCOOH. This high selective photocatalytic decomposition of NO ₃ ^– to N₂ may be a new pathway among the others reported so far, and it would be useful for environmental protection of water.     

Tin(IV) complexes ofSchiff bases derived from salicylaldehyde and aminoalcohols

11 and 12 molar reactions of tin(IV) chloride with theSchiff bases, HO–C₆H₄CHNROH [where R=–(CH₂)₂–, –CH₂–, –CH(CH₃)–, –(CH₂)₃–, and –CH(C₂H₅)CH₂–] have been studied in different stoichiometric ratios and derivatives of the type SnCl₄(SBH₂) and SnCl₄(SBH₂)₂ (whereSBH₂ represents theSchiff base molecule) have been isolated. These have been characterised by elemental analysis, conductivity measurements and I.R. spectral studies.     

Farbe und Konstitution bei anorganischen Feststoffen, 14. Mitt.: Die Lichtabsorption des zweiwertigen Kupfers in oxidischen Wirtsgittern

Zusammenfassung Um die Beziehungen zwischen der Lichtabsorption des zweiwertigen Kupfers nach isomorphem Einbau in ein oxidisches Wirtsgitter und dessen Konstitution aufzufinden, wurde Cu²⁺ in oktaedrischer (Cu _x Mg _1–x TiO₃, Cu _x Cd _1–x TiO₃, Cu _x Mg _1–x CaSiO₄, Cu _x Mg _1–x CaGeO₄, Cu _x Mg _2–x SiO₄, Cu _x Mg _2–x GeO₄) und tetraedrischer Koordination (Cu _x Zn_2–x SiO₄, Cu _x Mg _1–x Cr₂O₄) spektralphotometrisch untersucht. Die Farbkurven besitzen mindestens 2 Absorptionsbanden (Kristallfeldbanden) im längerwelligen und eine oft gut ausgeprägte Elektronenübergangsbande (charge transfer) im kürzerwelligen Spektralbereich. In einigen Fällen ist noch eine zweite Elektronenübergangsbande als Schulter zu erkennen. Es wurden auch Cu-haltige 2,3- und 2,4-Spinelle spektralphotometrisch untersucht (Cu _x Mg _1–x Al₂O₄, Cu _x Mg _1–x Ga₂O₄, Cu _x Cd _y Zn _1–x–y Al₂O₄, Cu _x Mg _2–x SnO₄, Cu _x Mg _2–x TiO₄, Cu _x Zn _1–x MgTiO₄, Cu _x Mg _1–x Cd _y TiO₄). Es zeigte sich, daß Cu²⁺ immer auf Tetraeder- und Oktaederlücken verteilt ist. Eine Aufweitung des Wirtsgitters durch isomorphen Einbau größerer Kationen bewirkt nicht immer eine IR-Verschiebung der Banden, sondern in einigen Fällen (Spinellphasen) auch eine UV-Verschiebung. Eine Sonderstellung nimmt das ägyptisch-Blau CuCaSi₄O₁₀ ein, da hier das Cu²⁺ von 4 O_2– in planarer Anordnung umgeben ist. Die Farbkurve weist 3 Maxima auf im Einklang mit der Kristallfeldtheorie.

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In order to find out relations between the lightabsorption of bivalent copper isomorphously incorporated into an oxidic host lattice and the constitution of this lattice, the spectrum of Cu²⁺ has been investigated in octahedral (Cu _x Mg_1–x TiO₃, Cu _x Cd _1–x TiO₃, Cu _x Mg _1–x CaSiO₄, Cu _x Mg _1–x CaGeO₄, Cu _x Mg _2–x SiO₄, Cu _x Mg _2–x GeO₄) and tetrahedral coordination (Cu _x Zn _2–x SiO₄, Cu _x Mg _1–x Cr₂O₄). The colour curves show at least 2 absorption bands within the region of longer wave length and a charge transfer band often well developed in the range of shorter wavelength. In some cases also a second charge transfer band becomes conspicuous as a shoulder. Copper containing 2,3- and 2,4-spinels have been also investigated (Cu _x Mg _1–x Al₂O₄, Cu _x Mg _1–x Ga₂O₄, Cu _x Cd _y Zn _1–x–y Al₂O₄, Cu _x Mg _2–x SnO₄, Cu _x Mg _2–x TiO₄, Cu _x Zn _1–x MgTiO₄, Cu _x Mg _1–x Cd _y Zn _1–y TiO₄). From the colour curve one can infer that Cu²⁺ occupies in the spinels always tetrahedral as well as octahedral interstices. A widening of the lattice does not effect always a shifting of the absorption bands towards IR but in some cases (spinel phases) also the inverse shifting will occur. An exceptional case represents the egyptian blue CuCaSi₄O₁₀ since in this lattice the Cu₂₊ are surrounded by four O^2– in a coplanar arrangement. The colour curve shows three absorption bands in agreement with the crystal field theory.

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Mit 20 Abbildungen     

New organosols of nickel sulfides,palladium sulfides,manganese sulfide,and mixed metal sulfides and their use in preparation of semiconducting polymer-metal sulfide composites

Organosols of NiS, PdS, and MnS in N,N-dimethylformamide were prepared by reaction of the metal acetate with H₂S. Organosols of mixed-metal sulfides (Zn _x Cd_1–x S, Hg _x Cd_1–x S, Hg _x Cu_1–x S, Cd _x Mn_1–x S, Hg _x Mn_1–x S, Hg _x Cd_1–x S, and Mn _x Zn_1–x S) were similarly obtained by reaction of mixtures of the metal salts with H₂S. The organosol of Zn_0.5Cd_0.5S contained particle with two particle size distributions centered at 6.5 nm and 29 nm, as revealed by Ar laser-scattering analysis. The metal sulfides are recovered by addition of Et₂O to the organosols. Zn _x Cd_1–x S thus obtained shows magnetic susceptibility in the range 0.5×10^–6–2.3×10^–6 emug^–1 depending on thex value. Addition of polymers to the organosols affords semiconducting films of metal sulfide-polymer composites.     

PE-CVD of Fluorocarbon/SiO Composite Thin Films Using C4F8 and HMDSO

Plasma copolymerization of hexamethyldisiloxane (HMDSO,(CH₃)₃-Si-O-Si-(CH₃)₃) and C₄F₈ was performed using an RF plasma enhanced chemical vapor deposition method for application to low dielectric constant intermetal dielectrics. Structure of the films was investigated by X-ray photoelectron spectroscopy and Fourier transform infrared (FT-IR) spectroscopy. The film composition was controlled gradually from fluorinated carbon to organic siloxane by changing the mixing ratio of HMDSO/Ar. Dielectric constant of the films ranged from 2–3.3. Thermal stability of the films, which was characterized by intensity loss of IR absorbance peak around 1000–1500 cm^–1 corresponding to C-F _n , Si-O-Si and Si-(CH₂)_n-Si bonds, was inferior to that from C₂F₄/HMDSO/Ar. In situ gasphase FT-IR spectroscopy revealed that there was a marked difference between the gas phase of C₄F₈/HMDSO/Ar and that of C₂F₄/HMDSO/Ar discharges. The IR spectrum of the former combination plasma contained a peak at 1250 cm^–1 with full width at half maximum as large as 150 cm^–1, which suggests that fluorocarbon particles and/or dusts are formed in the plasma. This suggests also that deposition precursors are not only CF _n (n = 1, 2, and 3) but also larger precursors such as C _x F _y (x > 1, y < 2x + 2) in C₄F₈/HMDSO/Ar discharges, which is presumably the cause of difference in thermal stability of the films prepared from C₄F₈/HMDSO/Ar and C₂F₄/HMDSO/Ar mixtures.     

Kristallstruktur von Trimethylisocyanursäure, (CH3NCO)3, und von Trichlorisocyanursäure-1/2-Ethylenchlorid, (ClNCO)3·1/2C2H4Cl2

X-ray crystal structure analyses of (CH₃NCO)₃ (M) and (ClNCO)₃·1/2C₂H₄Cl₂ (C) were carried out at room temperature (MoK, graphite monochromator, =0.71069 Å): 1.M=171.16, monochlinic, P2₁/c,a=14.848 (1) Å,b=13.400 (2) Å,c=8.149 (1) Å, =100.87 (1)°,V=1 592.3 ų,Z=8,F(000)=720,d _x =1.428 Mgm^–3, =76m^–1,R=6.51%,R _w =7.01% (964 reflections, 218 parameters). 2.M=281.89, monochlinic, P 2₁/c,a=9.416 (3) Å,b=5.728 (1) Å,c=18.199 (8) Å, =98.64 (2)°,V=970.4 Å₃,Z=4,F(000)=556,d _x =1.929 Mgm^–3, =1.11 mm^–1,R=3.96%,R _w =3.44% (605 reflections, 132 parameters). The ring systems together with the C atoms of the methyl groups in (M) and with the Cl atoms in (C) are planar and have D_3h-symmetry. Bond lengths and bond angles are discussed with regard to¹⁴N-NQR,³⁵Cl-NQR and vibrational spectroscopic data.

     

Study of hydroformylation of formaldehyde in the presence of rhodium catalysts byin situ IR spectroscopy and the kinetic technique

Carbonylrhodium complexes formed during hydroformylation of CH₂O from various rhodium precursors were investigated byin situ IR spectroscopy. It was found that under the conditions of the hydroformylation of CH₂O inN,N-dimethylacetamide (DMAA), RhH(CO)(PPh₃)₃, RhCl(CO)(PPh₃)₂, RhCl(PPh₃)₃, RhCl(CO)(PBu₃)₂, and [RhCl(CO)₂]₂ form complex systems that necessarily contain anionic complexes, [Rh(CO)₂L_x(DMAA)_y]^– (L = PPh₃, PBu₃,x = 1 to 2,y = 1 to 0; [Rh(CO)₄]^–). The participation of ionic structures in the hydroformylation of CH₂O, most likely, in the step of the activation of CH₂O, was proven by kinetic techniques.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1066–1069, June, 1995.     

Lithiated γ-O-functionalized propyl phenyl sulfides and sulfones of the type Li[CH(SOxPh)CH2CH2OR] (x = 0, 2). [Li{CH(SPh)CH2CH2Ot-Bu}(tmeda)] – A structurally characterized organolithium inner complex

Lithiation of O-functionalized alkyl phenyl sulfides PhSCH₂CH₂CH₂OR (R = Me, 1a; i-Pr, 1b; t-Bu, 1c; CPh₃, 1d) with n-BuLi/tmeda in n-pentane resulted in the formation of α- and ortho-lithiated compounds [Li{CH(SPh)CH₂CH₂OR}(tmeda)] (α-2a–d) and [Li{o-C₆H₄SCH₂CH₂CH₂OR)(tmeda)] (o-2a–d), respectively, which has been proved by subsequent reaction with n-Bu₃SnCl yielding the requisite stannylated γ-OR-functionalized propyl phenyl sulfides n-Bu₃SnCH(SPh)CH₂CH₂OR (α-3a–d) and n-Bu₃Sn(o-C₆H₄SCH₂CH₂CH₂OR) (o-3a–d). The α/ortho ratios were found to be dependent on the sterical demand of the substituent R. Stannylated alkyl phenyl sulfides α-3a–c were found to react with n-BuLi/tmeda and n-BuLi yielding the pure α-lithiated compounds α-2a–c and [Li{CH(SPh)CH₂CH₂OR}] (α-4a–b), respectively, as white to yellowish powders. Single-crystal X-ray diffraction analysis of [Li{CH(SPh)CH₂CH₂Ot-Bu}(tmeda)] (α-2c) exhibited a distorted tetrahedral coordination of lithium having a chelating tmeda ligand and a C,O coordinated organyl ligand. Thus, α-2c is a typical organolithium inner complex.Lithiation of O-functionalized alkyl phenyl sulfones PhSO₂CH₂CH₂CH₂OR (R = Me, 5a; i-Pr, 5b; CPh₃, 5c) with n-BuLi resulted in the exclusive formation of the α-lithiated products Li[CH(SO₂Ph)CH₂CH₂OR] (6a–c) that were found to react with n-Bu₃SnCl yielding the requisite α-stannylated compounds n-Bu₃SnCH(SO₂Ph)CH₂CH₂OR (7a–c). The identities of all lithium and tin compounds have been unambiguously proved by NMR spectroscopy (¹H, ¹³C, ¹¹⁹Sn).     

Magnetische Untersuchungen der Carbide TiC,ZrC, HfC,VC, NbC und TaC

Zusammenfassung Die magnetische Suszeptibilität an sehr reinen Mono-Carbidproben wird in Abhängigkeit vom Kohlenstoffdefekt gemessen. Mit zunehmendem Kohlenstoffdefekt werden TiC_1–x , ZrC_1–x , HfC_1–x und VC_1–x paramagnetischer. Extrapolation auf stöchiometrisches TiC führt auf Diamagnetismus. NbC_1-x und TaC_1–x zeigen einen davon abweichenden Verlauf; deren Suszeptibilitäten nehmen im wesentlichen mit steigendem C-Defekt ab und erreichen diamagnetische Werte. Eine Vorstellung zur Deutung des Suszeptibilitätsverlaufes bei TiC_1–x , ZrC_1–x , HfC_1–x und VC_1–x unter Berücksichtigung der Bindungsenergie, bei Übergangsmetallen wird entwickelt und eine Erklärung für das magnetische Verhalten von Mischcarbiden gegeben.Mit 2 Abbildungen     

Amino-Modified Silicate Xerogels Complexed with Cu(II) as Catalyst Precursors. Coordination State and Thermal Decomposition

The sol-gel process is a useful method for preparing two series of organically and co-ordinately modified xerogels of the types [CuN _n ]·N _5–n ·5xSiO_4/2 (n < 4) and [Cu(N–N)_n]·(N–N)_2–n ·2x SiO_4/2(n 2), where N = NH₂(CH₂)₃ SiO_3/2, N–N = NH₂(CH₂)₂NH·(CH₂)₃SiO_3/2 and x = [SiO_4/2]/[N] or [SiO_4/2]/[N–N]. The amino groups in the materials are coordinately active and participate partly in the coordination sphere of Cu(II) ions. The composition of the coordination sphere can be varied with the SiO_4/2 content and also as a result of the thermal decomposition of the organic residues at higher temperatures.Because the xerogel materials are considered to be catalyst precursors, this study is focused on their coordination and thermal properties. The prepared xerogels, such as silica, aminated silicates with N and N–N, as well as those entities complexed with Cu(II), were characterised by FT-IR spectroscopy. During gelation and thermal decomposition the materials were analysed by electron paramagnetic resonance (EPR) spectroscopy. The xerogels were additionally studied by UV-Vis absorption spectroscopy. The gaseous products of the thermal decomposition of these materials in an Ar atmosphere were investigated by the use of FT-IR spectroscopy coupled with TG and DTG thermal analysis. These data were complemented by temperature-programmed decomposition (TPDec) in a 2% O₂ + 98% Ar stream coupled with quadrupole mass spectroscopy.     

Nuclear magnetic resonance and high-performance liquid chromatographic evaluation of polymer-based stationary phases immobilized on silica

Three poly(ethylene-co-acrylic) acid copolymers (–CH₂CH₂–)_x[CH₂CH(CO₂H)–]_y with different chain lengths and mass fractions of acrylic acid were covalently immobilized as stationary phases on silica via two variants of spacer molecules (3-aminopropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane). Different mobilities of the alkyl chains in the stationary phases were observed using ¹³C solid-state NMR spectroscopy. The stationary phases with more rigid trans-ordered alkyl chains had better selectivity for geometric -carotene and xanthophyll isomers (provitamin A derivatives). Also, all the separations of the analytes were affected by polar interactions with the chromatographic sorbent. This was further proved by separating more polar cis/trans retinoic acid isomers (vitamin A derivatives). ¹³C high-resolution/magic-angle spinning (HR/MAS) NMR measurements of the chromatographic sorbents suspended in the mobile phase confirmed a dependence of molecular shape recognition ability on alkyl chain conformation.     

Effect of Metal Alkoxide Complexes on Condensation Reactions of Hydrolyzed Phenyltriethoxysilane

Metal alkoxide complexes, in which alkoxy groups were substituted with ethyl acetoacetate (EAcAc), were found to accelerate condensation reactions of hydrolyzed phenyltriethoxysilane (PTES) and affect the structure of phenylsiloxane networks. The ²⁹Si NMR study revealed that the acceleration effect increased in the order Al(O-sec-C₄H₉)_3–x (EAcAc) _x < Ta(OC₂H₅)_5–x (EAcAc)_x < Ti(OC₂H₅)_4–x (EAcAc) _x . However, the GPC study revealed that the solution contained the high molecular weight species in the order Al(O-sec-C₄H₉)_3–x (EAcAc) _x < Ti(OC₂H₅)_4–x (EAcAc) _x < Ta(OC₂H₅)_5–x (EAcAc) _x . In the case of Ti(OC₂H₅)_4–x (EAcAc) _x , the smaller size of phenylsiloxane networks with a low content of silanol groups was formed in the solution. In the case of Ta(OC₂H₅)_5–x (EAcAc) _x , the larger size of phenylsiloxane networks with a high content of silanol groups was formed in the solution. In the case of Al(O-sec-C₄H₉)_3–x (EAcAc) _x , the small size of phenylsiloxane networks with a high content of silanol groups was formed in the solution. During gelation, the catalytic effect of the metal alkoxide complexes on the development of phenylsiloxane networks was also found. However, the average molecular weight of the gels increased in the order Ta(OC₂H₅)_5–x (EAcAc) _x < Ti(OC₂H₅)_4–x (EAcAc) _x Al(O-sec-C₄H₉)_3–x (EAcAc) _x . The metal alkoxide complexes were hydrolyzed and finally incorporated into the phenylsiloxane networks of gels to form M—O—Si bonds, which were indicated by the results of FT-IR analysis.     

Heterometallic Alkoxide Complexes of Variable Composition—A New Way to Ultrafine Powders of Metal Alloys

The anodic oxidation of Re metal in MeOH (Me = CH₃) provides a mixture of Re₂O₃(OMe)₆ and Re(V) oxoalkoxides that on storage or on heating give insoluble and air stable Re₄O_6–y (OMe)_12+y (I). I can be also obtained by reaction of Re₂O₇ with MeOH. In the presence of MoO(OMe)₄, a heterometallic complex ReMoO₂(OMe)₇(II) is formed as intermediate, the final product being Re_4–x Mo _x O_6–y (OMe)_12+y (III). The electrosynthesis in the presence of WO(OMe)₄ gives Re_4–x W _x O_6–y (OMe)_12+y (IV) only at very high Re : W ratios in solutions and the W content varies in one and the same sample. The dissolution of Re₂O₇ in the solutions of MO(OMe)₄, M = Mo,W in toluen on reflux yields Re_4–x M _x O_6–y (OMe)_12+y with uniform Re : M distribution. The cocrystallization of MoO(OMe)₄ and WO(OMe)₄ yields (Mo,W)O(OMe)₄ (V) with almost uniform Mo : W distribution. The thermal decomposition of II and III in inert atmosphere gives fine powder of the (Re,Mo)O₂ phase. The reduction with hydrogen gas converts II and III into an ultrafine powder of Re–Mo alloy at temperatures below 400°C. The latter can be sintered into compact metal at 800–900°C.