Evgeniya V. Suslova

Purposeful construction versus self-assembly in approaches to single source precursors of spinel materials. Synthesis, structure and stability studies of MIIAl2(acac)3(OiPr)4(OAc), MII= Mn, Co, Zn – a new class of heterometallic heteroleptic alkoxide complexes

The reaction of Mn(acac)3 with 3 eq. of Al(OiPr)3 in toluene at reflux provided with minor yield single crystals of MnAl2(acac)3(OiPr)4(OAc)(C7H8)0.5 (1), incorporating into the molecular structure the acetate ligand originating from oxidation of the OiPr-groups. 1 was obtained with high yield (76%) via the reaction of Mn(acac)3 with 2.2 eq. of Al(OiPr)3 with subsequent addition of 1 eq. of HOAc to the reaction mixture cooled to room temperature. The analogs of 1, CoAl2(acac)3(OiPr)4(OAc)(C7H8)0.5 (2), and ZnAl2(acac)3(OiPr)4(OAc)(C7H8)0.5 (3), were obtained with almost quantitative yields by reaction of the corresponding MII(acac)2 with 2 eq. of Al(OiPr)3 in toluene at reflux with subsequent addition of 1 eq. of Hacac and 1 eq. of HOAc after cooling the reaction mixture to the room temperature. In the molecules 1–3 the late transition metal atom is tetrahedrally coordinated (η2-acac plus 2 bonds to μ-OiPr-groups), and the Al atoms have a slightly distorted octahedral coordination (hexacoordinated) (η2-acac plus 3 bonds to μ-OiPr-groups plus one bond to μ-OAc-group). 1–3 are stable to solvolysis in toluene and are volatile under reduced pressure. Thermal decomposition of CoAl2(acac)3(OiPr)4(OAc)(C7H8)0.5 leads to nanoparticles of CoAl2O4, while homogeneous coatings of the spinel can be easily obtained using MOCVD.

CO2 hydrogenation over cobalt-containing catalysts

Carbon dioxide hydrogenation over catalysts consisting of 0.56–45 wt % cobalt supported on carbon nanotubes (CNTs), carbon nanofibers, few-layer graphite fragments, or CNTs–Al2O3 composites has been investigated. All of the Co/support catalytic systems have been characterized by temperature-programmed reduction, transmission electron microscopy, and scanning electron microscopy. Under the conditions of our catalytic experiment (1 atm, 180–500°C), the CO2 hydrogenation products are CH4 and/or CO and the activity of the catalysts depends on the size and phase state of the cobalt particles. The CNTs-supported materials containing less than 5 wt % Co are catalytically inactive because of the amorphism of the metal. They can be activated by cobalt crystallization by means of heat treatment. The size of the cobalt particles deposited on the carbon supports is about 4 nm. Methods of functionalizing the carbon nanomaterial surface for additional stabilization of metal nanoparticles are suggested.

Synthesis and X-ray single crystal study of Co2Al2(OiPr)6(acac)4-first representative of a new structure type for the heterometallic alkoxide complexes

Abstract The interaction of Co(acac)2with Al ( O i Pr ) 3 in 1:1 ratio in toluene on reflux provided with quantitative yield a new heterometallic heteroleptic alkoxide complex, Co 2 Al 2 ( O i Pr ) 6 ( acac ) 4 (I), displaying the so far unprecedented linear chain structure with a M′(μ-OR)2M(μ-OR)2M(μ-OR)2M′core. I appears to be a promising precursor for cobalt oxide–cobalt spinel nanocomposite materials.

Effect of cobalt weight content on the structure and catalytic properties of Co/CNT catalysts in the fischer–tropsch synthesis

Cobalt-based Fischer–Tropsch synthesis (FTS) catalysts containing 1 to 40 wt % cobalt supported on multi-walled carbon nanotubes (CNTs) have been investigated. The CNTs have been characterized by low-temperature nitrogen adsorption, scanning electron microscopy, and X-ray photoelectron spectroscopy. All catalysts have been prepared by impregnating, with an ethanolic solution of cobalt nitrate, the CNTs preoxidized with concentrated nitric acid and have been tested in the FTS at 220°C and atmospheric pressure. Correlations have been established between the cobalt weight content of the catalyst and the Co particle size determined by transmission electron microscopy and X-ray diffraction. The Co content and particle size have an effect on the activity and selectivity of the catalyst and on the target fraction (C5+) yield in the FTS. The highest CO conversion is observed for the catalyst containing 20 wt % Co; the highest selectivity and activity, for the catalyst containing 5 wt % Co; the highest C5+ yield, for the catalyst containing 10 wt % Co.

Electrosynthesis of tin(II) alkoxides

The anodic dissolution of tin metal in absolute alcohols yields oxoalkoxides with the general formula Sn6O4(OR)4 (R = Me (1), Et (2), i-Pr (3)) and orthoalkoxides with the general formula Sn(OR)2 (R = n-Bu (4), C2H4OMe (5)). According to X-ray crystallographic data, the molecule of Sn6O4(OEt)4 (2) is an octahedral [Sn6] cluster with alternating oxo and OEt groups on its faces. The mass spectra of 1 and 2 indicate the presence of fragments of the hexanuclear oxoalkoxides.

New Effective Catalytic Materials based on Modified Heterosubstituted Multiwall Carbon Nanotubes

Present work deals with development of the synthetic procedures for nitrogen and phosphorous substituted multiwall carbon nanotubes (MWCNT) by pyrolytic technique followed by surface modification by cobalt nanoparticles and utilization of the composite obtained in Fischer-Tropsch (FT) synthesis. It is shown that heterosubstitution in CNT structure changes the electron capacity and acid-based properties of the system, allow effectively stabilize metal nanoparticles of 2-4 nm size and yields to thermally stable and effective catalyst for cobalt FT synthesis.

Gallium alkoxides: Synthesis and properties

Compounds Ga(OR)3 (R = Me, Et, Pri, Bun, C2H4OMe) were synthesized by exchange reactions between gallium chloride and alkali metal alkoxides, the reetherefication of Ga(OPri)3 and Ga(OC2H4OMe)3 by other ROH (R = Me, Et), and anodic dissolution of metallic gallium in the presence of a electroconductive additive (LiCl, Bu4NBr). When solid GaCl3 is introduced into an alcoholic solution of NaOEt, stable soluble gallium oxoalkoxyhalides are formed. The same reaction with a GaCl3 solution in toluene or electrochemical synthesis produces nonvolatile Ga(OEt)3 samples, which have the polymer zigzag configuration [Ga(OR)4/2(OR)]∞. Mass spectrometry shows that only Ga(OPri)3 and freshly prepared X-ray amorphous Ga(OEt)3 samples (produced by reetherefication) are transferred to the gas phase. The spectra of the latter contain ions generated by penta-and hexanuclear oxoalkoxide molecules, along with fragments of orthospecies [Ga(OEt)3]2−4. IR spectra are described for all compounds synthesized.

Gallium isopropoxide: Synthesis, properties, “coordination polymerism”. New pentanuclear gallium oxoisopropoxochloride

Conditions for the synthesis of gallium isopropoxide (I) by anodic dissolution of the metal in i-PrOH (in the presence of Bu4NBr supporting electrolyte) and by exchange reaction of GaCl3 with i-PrONa were studied. In the latter case, the crude product was a waxy substance (II) infinitely soluble in the alcohol and hydrocarbons and containing 12–30% Cl, which cannot be removed by adding an excess of i-PrONa due to the formation of insoluble NaGa(OPr-i)4. During 1.5–2 months, II is solidified to give non-melting nonvolatile amorphous product (III) poorly soluble in the alcohol. Upon heat treatment of II in vacuum, compound I is distilled off as an oily liquid consisting, according to mass spectrometry, of [Ga(OPr-i)3]2 dimer molecules. It can be retained for a long period of time in the presence of the [Ga(OPr-i)3]4 tetramer crystals. The existence of oligomeric molecules of different size up to polymers (“coordination polymerism”) in the materials is related to the possibility of tetrahedral or octahedral coordination of the metal atom. From concentrated solutions of components, the oxoalkoxochloride [Ga5(µ5-O)(µ-OPr-i)8Cl5] (IV) is crystallized. Its molecule is a flattened tetragonal pyramid. The equatorial plane formed by four gallium atoms has the µ5-O group at the center. The axial Ga atom has an octahedral coordination. All eight sides of the pyramid are drawn together by the µ-OPr-i groups, and the chlorine atoms occupy the terminal positions. (CIF file CCDC no. 693282.)

Lanthanum alkoxides. Crystal structure of [La6(μ6-Cl)(μ3-OPri)2(μ-OPri)9(OPri)6]

La(OR)3 (R = Me, Et, Pri, or C2H4OMe) has been synthesized via direct and electrochemical dissolution of metallic lanthanum in alcohols (in the presence of I2 or a HgCl2/HgI2/Hg(OAc)2 mixture catalysts or Bu4NBr or Et3BzNCl electrochemical additives, respectively). Lanthanum methoxide, ethoxide, and n-buthoxide have been synthesized via etherification of La(OPri)3 and were characterized by IR spectroscopy and mass spectroscopy. The composition and physicochemical characteristics of lanthanum isopropoxide can vary over broad ranges depending on a method of its synthesis. The electrochemical dissolution of lanthanum in isopropanol or in the presence of I2 catalytic amounts yields an insoluble polymeric product, and the synthesis of “La(OPri)3” in the presence of a HgCl2/HgI2/Hg(OAc)2 mixture results in the crystallization of La6Cl(OPri)17, whose composition and structure have been established by X-ray diffraction. In a La6(μ6-Cl)(μ3-OPri)2(μ-OPri)9(OPri)6 molecule, lanthanum atoms form a trigonal prism centered by a chlorine atom (La–Cl, 3.14–3.15 Å), and isopropyl groups are μ3-bridging, μ2-bridging or terminal (La–O, 2.537, 2.435, and 2.152 Å, respectively).

On the interaction of tetraethoxosilane with metal alkoxides: Sol-gel synthesis of alkaline-earth metal silicates

Physicochemical analyses (solubility method, conductometry, and IR spectroscopy) revealed no complex formation in M(OR)n-Si(OR)4-ROH systems (M = Na, Ba, Al; R = Et, Pri), unlike in the systems containing alkoxides of two metals. IR and NMR spectroscopy showed that Si(OR)4 became reactive only due to microhydrolysis, which is accompanied most likely by the formation of intermediates (asymmetric molecules [Si(OH)n(OR)4 − n]). The hydrolysis was studied for model systems M(OEt)2 − si(OEt)4 (M = Ba, Ca), and conditions for the synthesis of silicates were optimized.