Effect of hydrothermal treatment on the composition and structure of Pt(IV) hydroxo complexes as model precursors of the active component in Pt/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

The influence of hydrothermal treatment conditions (temperature, duration, acidity of the medium) on the structural and chemical transformations of the complex H₂[Pt(OH)₆] was studied. The composition and structure of the resulting compounds were determined by several physicochemical methods. Thermal analysis coupled with mass spectrometry showed that, as the hydrothermal treatment temperature is raised from 25 to 120 and 150°C, the product composition in terms of empirical formulas changes as follows: PtO₂ · 4H₂O → PtO₂ · 3.5H₂O → PtO₂ · 1.5H₂O. X-ray diffraction and UV and IR spectroscopy demonstrated that the changes in the chemical composition are accompanied by the amorphization of the structure and Pt-O bond strengthening. X-ray structure determination using the radial electron density distribution method showed that polynuclear species ～10–15 Å in size with a structure similar to that of orthorhombic PtO₂ form in the complexes subjected to “hard” hydrothermal treatment (T ≥ 150°C).     

Synthetic and structural studies on some 1,3-diselena- and 1,3-dithia-[3]ferrocenophanes of germanium and tin. crystal and molecular structure of 1,3-diselena-2,2- dichlorogermyl-[3]ferrocenophane

A series of [3]ferrocenophanes of general formula Fe(C₅H₄X)₂YCl₂ and the spiro compounds [Fe(C₅H₄X)₂]₂Ge (X = S, Se; Y = Ge, Sn) have been prepared by the reaction of ferrocene 1,1′-dithiol and ferrocene 1,1′-diselenol with tetrahalides of germanium and tin. Spectroscopic properties of the compounds are reported. In solution, the compounds are fluxional by a bridge reversal process. The crystal structure of 1,3-diselena-2,2-dichlorogermyl-[3]ferrocenophane at 163 K. has been determined by X-ray diffraction methods. At that temperature, crystals have space group P2₁/n with a 6.222(3), b 16.156(13), c 12.968(4) Å, β 97.53(1)° and Z = 4. Least-squares refinement gave R = 0.033 for 2834 unique significant reflections whose intensities were measured by counter diffractometry. The two SeGe bond lengths are 2.323 and 2.325(1) Å, with GeCl 2.148 and 2.161(1) Å. The SeGeSe bond angle is 118.2(1)°, ClGeCl 104.7(1)°, and SeGeCl angles range from 106.2 to 109.8(1)°. The SeC bond lengths are 1.901 and 1.904(5) Å, with CSeGe angles of 95.8 and 96.5(2)°. The cyclopentadienyl rings are in an eclipsed conformation with a mean twist angle of 2.7°, and are inclined to one another at 6.1°. The Se atoms are displaced from the ring planes by 0.17 and 0.20 Å yielding a non-bonded intramolecular Se…Se contact of 3.99 Å.     

Kristall-und molekülstrukturen zweier modifikationen de hexaphenyldigermylsulfids (C6H5)3GeSGe(C6H5)3

en Two differnt crystal modifications of hexaphenyldigermanium sulfide (C₆H₅GeSGe(C₆H₅)₃ (I and II were obtained by crystallization from hot benzene/methanol or form ethanol at 20°C. Single crystal X-ray structural analyses for both I (low temperature data at ?130°C) and II (at 20°C) (I, R = 0.046; II, R = 0.048) were performed. I is monoclinic, P2¹/c, with a = 11.020(3), b = 15.473(3), c 18.606(3) »,π = 106.92(2)°, Z = 4; II is orthorhombic, P2₁2₁2₁, with a = 2.617(2), b = 17.345(3), c = 18.408(3) », Z = 4.The molecules have different conformeric structures with respect to a rotation of the (C₆H₆)₃Ge groups around the Ge bonds with very similar bond lenghts and angles. Bond data for I(II) are: GeS 2.212(1) and 2.261(1) » (2.227(2) and 2.240(2) »); GeC 1.933(4) ? 1.971(4), mean 1.945(5) » (1.931(7)?1.954(7), mean 1.943(4) »); GeSGe 111.2(1)° (110.7(1)°). The Ge bond lenghts are comparable to those in thiogermanates and do not indicate significant π-bond contributions.     

Hydrothermal treatment of Zr,Ti, Sn and Ge hydrogenphosphates

The Zr, Ti, Sn and Ge hydrogenphosphates, generally prepared in a crystalline form by the refluxing method, have been submitted to hydrothermal treatment at 180° and 300°C in order to observe if the preparation time can be shortened maintaining their chemical composition and their -structure. Simultaneous TG and DTA together with XRD revealed to be very suitable techniques for the characterization of the obtained products.Zr phosphate is the most stable and gives in all conditions the -monohydrated hydrogenphosphate phase. Similar behaviour for the Ti phosphate at 180°C, while at 300°C the compound transforms into -Ti(HPO₄)₂·2H₂O. Sn phosphate, even on maintaining its -structure, gives rise to more and more dehydrated phases on the increasing of the temperature of the HT and the concentration of the used phosphoric acid.Ge hydrogenphosphate resulted the least stable under hydrothermal conditions, since even at 180°C it gives rise to GeOHPO₄. Because of the easy hydrolyzability of Ge, the hydrothermal method is not a way to prepare the crystalline -germanium hydrogenphosphate.Thanks are due to C. N. R. — Progetto Finalizzato Materiali Speciali per Tecnologie Avanzate for the financial support.     

The Formation and Structural and Phase Transformations of Aluminum Hydroxy Species in Hydrothermal Synthesis under Conditions of Homogeneous Precipitation from Sulfate Solution

By X-ray powder diffraction analysis, Raman spectroscopy, scanning and transmission electron microscopy, and low-temperature nitrogen adsorption method, it was studied how the temperature of hydrothermal synthesis affects the phase composition of precursor species and the structure and morphology of alumina obtained under conditions of low-temperature hydrothermal synthesis at 90–130°C in the system 0.5Al₂(SO₄)₃ · 18H₂O∥0.2C₁₆H₃₃(CH₃)₃NBr∥5i-PrOH∥85H₂O∥2CO(NH₂)₂. It was found that, at T_HTS = 90–110°C, alumina microspheres with globular structure form from X-ray amorphous hydrated alumina with an admixture of NH₄Al₃(SO₄)₂(OH)₆. It was shown that needle-like alumina particles with slitlike pores form from NH₄Al(OH)₂CO₃ obtained at T_HTS = 110–120°C. At T_HTS = 130°C, under conditions of the formation of γ-AlOOH, alumina spherulites constituted by needle-like particles with block–layer structure form. It was determined that the temperature range of the formation of metastable crystalline modifications of alumina is controlled by the phase composition of hydrothermal synthesis products.     

Consecutive preparation of hydrochar catalyst functionalized in situ with sulfonic groups for efficient cellulose hydrolysis

Hydrochars in situ functionalized with –SO₃H groups were generated from kenaf core via a low-temperature hydrothermal carbonization process of 105 °C with a consecutive catalysis of H₂SO₄. The micro-morphology of the hydrochars was strongly affected by the sulfuric acid concentration. Sphere-like particles with size varying between 200 nm and 1 μm were obtained when the acid concentration was 52 wt%. Acid density of the hydrochar increased with the H₂SO₄ concentration increasing. The presence of considerable acidic groups of –SO₃H, –COOH, and –OH on the surface of hydrochars was evidenced by Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. The hydrochar obtained can be used directly for effective catalytic hydrolysis of cellulose without any post-modification. This study proposed a promising sustainable and cost-effective route for facile production of acidic hydrochar from crude plant with tunable properties.     

Sol-Gel Synthesis of Ge Nanocrystals-Doped Glass and Its Photoluminescence

Ge nanocrystal-embedded SiO₂ glasses were prepared by a sol-gel process. The glasses synthesized through the hydrolysis of Si(OC₂H₅)₄ and GeCl₄ were heated in H₂ gas atmosphere at 500 to 800°C, in which Ge⁴⁺ ions were reduced to precipitate nanosized Ge crystals with the size smaller than 10 nm diameter. Glasses doped with Ge nanocrystals of diameter of ≈5 nm showed the optical absorption edge at ≈2.8 eV and a broad photoluminescence exhibiting the peak at around 2.2 eV. Large Ge crystals precipitated by heating above 800°C showed no photoluminescence.     

Synthesis and characterization of MIIU3O10 · nH2O (MII = Mg, Mn, Co, Ni, Cu, Zn, Cd) triuranates

Individual crystalline phases of composition M^IIU₃O₁₀ · nH₂O were prepared by reacting schoepite UO₃ · 2.25H₂O with aqueous solutions of Mg, Mn, Co, Ni, Cu, Zn, or Cd nitrates under hydrothermal conditions at 200°C. The composition and structure of the resultant compounds were determined by hightemperature X-ray diffraction, IR spectroscopy, scanning calorimetry, and chemical analysis; the dehydration and thermal destruction of the compounds were studied.     

Sodium-doped vanadium oxide nanorods

Sodium-Doped vanadium oxide nanorods of composition Na_0.44V₂O₅ · 1.6H₂O were manufactured under hydrothermal conditions (T = 150-180°C, τ = 30–50 h). Particle diameters are 20–80 nm; lengths are 0.25–1.5 μm. Particles have a layered structure with interlayer distances of 10.71 ± 0.03 Å. X-ray photoelectron and IR spectra, electrical conductivity, and thermal properties of nanorods were studied.     

Thermochemistry of the hydrates of k2CoCl4

A study of the dissociation pressure of crystalline K₂CoCl₄·2H₂O. The reactions can be summed up as K₂CoCl₄·nH₂O(c) = K₂CoCl₄·mH₂O(c)+(nm)H₂O (v). Below 50°C, n = 2 and 1, m = 1 and 0, above 50°C, n = 2 and m = 0. Below 50°C, the dihydrate is octahedral, the monohydrate and anhydrous compounds are tetrahedral. ΔH° and ΔS° are respectively 7.0 kcal and 14.2 e.u. for the loss of the first mole of water and 12.7 kcal and 32.0 e.u. for the loss of the last mole of water. Above 50°C, ΔH° and ΔS° are respectively 29.8 kcal and 77.6 e.u. for the loss of both waters. The changes in structure are discussed using the spectral and magnetic properties as indications for structural changes.     

Uranyl orthovanadate of composition (UO2)3(VO4)2 · 4H2O: Synthesis and characterization

Uranyl orthovanadate of composition (UO₂)₃(VO₄)₂ · 4H₂O was prepared by heating uranovanadic acid HVUO₆ · 2H₂O under hydrothermal conditions at 200°C. X-ray fluorescence analysis, high-temperature X-ray diffraction, scanning calorimetry, and IR spectroscopy served to study dehydration and to determine the structure, X-ray diffraction, and spectroscopic characteristics of dehydration products.     

V<Subscript>3</Subscript>O<Subscript>7</Subscript> · H<Subscript>2</Subscript>O oxide nanostructures: Synthesis and study

Nanorods of orthorhombic V₃O₇ · H₂O with the parameters a = 16.805 Å, b = 9.428 Å, and c = 3.660 Å are prepared under hydrothermal conditions (T = 180–190°C, τ = 30–40 h) from the V₂O₅ · nH₂O/H₂C₂O₄ · 2H₂O composite. The particle diameter is 40–70 nm, and the length is several micrometers. The IR spectra, electric conductivity, and thermal properties of the nanorod powder are studied. In air V₃O₇ · H₂O begins to decompose at temperatures above 150°C, and at 350°C nanobelts V₂O₅ 40–100 nm wide and 40 µm long are formed. A mechanism of nanostructure formation is suggested.     

Clathrate formation in the series of systems diisopentyldibutylammonium halide-water

Three clathrate hydrates: (i-C₅H₁₁)₂·(C₄H₉)₂NCl·38H₂O (mp 20.5°C), (i-C₅H₁₁)₂·(C₄H₉)₂NCl·32H₂O (mp 22.2°C), and (i-C₅H₁₁)₂·(C₄H₉)₂NCl·27H₂O (mp 23.8°C) were detected in the system diisopentyldibutylammonium chloride-water. Crystals of all the compounds were isolated, and their composition was determined. The size effect of the halide anions (F^?, Cl^?, and Br^?) on the properties of related compounds was considered.     

Über polygermane: XIV. Polygermane als nebenprodukte der Grignard-reaktion von PhMgBr mit GeCl4

The synthesis of GePh₄ and Ge₂Ph₆ by Grignard reaction in THF or ether/toluene leads to the by-products Ge₃Ph₈ (up to 11%) and Ge₄Ph₁₀ (up to 18%) which is dependant on using an excess of Mg. A quantitative analysis of the resulting products by HPLC and a semipreparative separation by column, flash, and HPL chromatography is described. The crystal structures of Ge₃Ph₈ (R = 0.075) and Ge₄Ph₁₀ · 2C₆H₆ (R = 0.054) have been determined. Ge₄Ph₁₀ has C_i symmetry and both chain conformations are well staggered (49–70° for Ge₃Ph₈, 53–66° for Ge₄Ph₁₀). The GeGe distances and GeGeGe angles are 244 pm and 121° (Ge₃Ph₈), and 246 pm and 118° (Ge₄Ph₁₀).     

Effect of hydrothermal treatment conditions on formation of nickel hydrogermanate with platy morphology

Study of the phase composition and morphology of products formed in a hydrothermal treatment of the Ni(OH)₂–GeO₂–H₂O system with Ni/Ge cation molar ratios of 1, 1.5, and 2 in water and in aqueous solutions of HCl and NaOH demonstrated that the hydrothermal treatment products are composed of particles with plate-like morphology and average plate thickness of 40 nm and width of 500 nm. In this case, the phase composition of the products depends both on the molar ratio between the Ni and Ge cations and on the composition of the hydrothermal medium. Single-phase samples with structure similar to that of lizardite were obtained by treatment of a mixture with Ni/Ge = 1 in an alkaline medium or in a mixture with Ni/Ge = 1.5, irrespective of the composition of the medium. With the excess of GeO₂, a talc-like phase is formed, whereas with the excess of Ni(OH)₂, the samples contain crystalline nickel hydroxide in addition to the lizardite-like phase. Possessing magnetic and semiconductor properties, the single-phase nanopowders obtained in the study are promising as functional nanodispersed fillers of composite materials.     

Synthesis and characteristics of the dioxonium salt based on tartratogermanate acid. Crystal and molecular structure of (H5O2)[(H2O)2Ge(μ-Tart)2Ge(OH)] · 4H2O

Tartratogermanate acid was obtained for the first time as the dioxonium complex (H₅O₂)[(H₂O)₂Ge(??-Tart)₂Ge(OH)] · 4H₂O (I) by the reaction of germanium tetrachloride with D-tartaric acid (H₄Tart) in 85% acetic acid. The complex was characterized by elemental analysis data, thermogravimetry, and IR spectroscopy. X-ray diffraction analysis for I was performed. The crystals are orthorhombic, a = 15.862(3) ?, b = 13.401(3) ?, c = 8.6800(17) ?, V = 1845.1(6) ?³, Z= 4, space group P2₁2₁2, R1= 0.0520 for 5152 reflections with I > 2??(I). Compound I is composed of the dimeric complex anions [(H₂O)₂Ge(??-Tart)₂Ge(OH)]^?, dioxonium cations, and water molecules of crystallization. In the anion, the Ge(1) (CN = 6) and Ge(2) (CN = 5) atoms are linked by two chelating bridging fully deprotonated tartaric acid ligands through two carboxyl (average Ge-O, 1.883(4) and 1.893(4) ?, respectively) and two alcohol (average Ge-O, 1.859(4) and 1.779(4) ?, respectively) oxygen atoms. The coordination polyhedron of Ge (1) is completed to a distorted octahedron by the oxygen atoms of two water molecules (Ge(1)-O(H₂O), 1.933(4) and 1.854(3) ?). The Ge(2) coordination polyhedron is trigonal bipyramid. Its base is formed by two alcohol oxygen atoms of two bridging Tart^4? ligands and the oxygen atom of the terminal hydroxy group (Ge-O, 1.764(4) ?). The axial positions are occupied by the carboxyl oxygen atoms of the Tart^4? ligands (the O(5)Ge(2)O(11), 176.84(16)°). In the crystal, the structural units are combined by hydrogen bonds to a three-dimensional framework.     

Effect of Ag-doping of nanosized FeMgO system on its structural, surface, spectral, and catalytic properties

The effects of Ag-doping on the physico-chemical, spectral, surface, and catalytic properties of the FeMgO system with various Fe₂O₃ loadings were investigated. The dopant (Ag) molar ratio varied between 0.01 % and 0.05 %. The techniques employed for characterisation of catalysts were TG/DTG, XRD, ESR, N₂ adsorption at ?196°C, and catalytic decomposition of H₂O₂ at 25?C35°C. The results obtained revealed that the investigated catalysts consisted of nanosized MgO as the major phase, apart from the MgFe₂O₄ and/or Fe₃O₄ phases. ESR result of the FeMgO system revealed the presence of paramagnetic species as a result of Ag-doping. The textural properties including SBET, porosity and St were modified by Ag-doping. The doping process with Ag-species improved the catalytic activity of the FeMgO system. Increasing the calcination temperature from 400°C to 800°C increased the catalytic activity (k*_{30 °C}) of 0.05 AgFeMgO in H₂O₂ decomposition by 21.2 times.     

Thermal behaviour of malonic acid,sodium malonate and its compounds with some bivalent transition metal ions

Characterization, thermal stability and thermal decomposition of transition metal malonates, MCH₂C₂O₄·nH₂O (M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II)), as well as, the thermal behaviour of malonic acid (C₃H₄O₄) and its sodium salt (Na₂CH₂C₂O₄·H₂O) were investigated employing simultaneous thermogravimetry and differential thermal analysis (TG-DTA), differential scanning calorimetry (DSC), infrared spectroscopy, TG-FTIR system, elemental analysis and complexometry. The dehydration, as well as, the thermal decomposition of the anhydrous compounds occurs in a single step. For the sodium malonate the final residue up to 700 °C is sodium carbonate, while the transition metal malonates the final residue up to 335 °C (Mn), 400 °C (Fe), 340 °C (Co), 350 °C (Ni), 520 °C (Cu) and 450 °C (Zn) is Mn₃O₄, Fe₂O₃, Co₃O₄, NiO, CuO and ZnO, respectively. The results also provided information concerning the ligand's denticity, thermal behaviour and identification of some gaseous products evolved during the thermal decomposition of these compounds.     

Ammonium and potassium citratogermanates(IV): Synthesis, chemical compositions, and structures. The crystal structures of (NH4)[Ge(OH)(H2Cit)2] · H2O and K4[Ge(HCit)2(H2Cit)] · 3H2O

Methods for the synthesis of ammonium citratogermanate (NH₄)[Ge(OH)(H₂Cit)₂] · H₂O (I) and potassium citratogermanate (K₄[Ge(HCit)₂(H₂Cit)] · 3H₂O (II), where H₄Cit is citric acid) in aqueous MeCN were developed. The individuality, chemical composition, and thermal stability of complexes I and II were proved by elemental analysis, thermogravimetry, and IR spectroscopy. According to X-ray diffraction data, the coordination numbers of the Ge atoms are 5 and 6 and their coordination polyhedra are a square pyramid and an octahedron in complexes I and II, respectively. In both complexes, the Ge atom coordinates the deprotonated OH group and the α-carboxyl group of the ligands H _n Cit^4?n to form five-membered chelate rings. Hydrogen bonds in I as well as potassium cations in II serve to unite these complexes into frameworks.     

Coordination polymers of rare-earth elements with 2-aminoterephthalic acid

Coordination polymers of REEs with 2-aminoterephthalic acid [Ln₂(C₈H₅NO₄)₃(H₂O)₅] _n · 2nH₂O (Ln = Eu, Gd, or Tb) and [Y₂(C₈H₅NO₄)₃(H₂O)₄] _n · 4nH₂O were prepared by hydrothermal synthesis. Studies of the thermal behavior of these coordination polymers have shown that the removal of the solvate and the coordinated water molecules occurs at heating to 250°C and dehydratation products are stable up to 400°C. Detailed studies of the magnetic behavior of Eu, Gd, and Tb polymers were performed.