Studies on the thermal decomposition of the silver group of alkali metal nitritocobaltates(III)

The thermal decomposition of nitritocobaltate(III) of the silver group of general formula M₂Ag[Co(NO₂)₆] (where M = K⁺, NH⁺₄, Rb⁺ or Cs⁺) has been investigated. Based on the thermal curves of the investigated compounds and chemical and diffractometric analysis, the mechanism of thermal decomposition has been determined. The results obtained indicate that the decomposition proceeds in three stages. As a result of decomposition in the first stage (300°C), nitrates of alkali metals, metallic silver and Co₃O₄ are formed. In the second stage (500°C), a partial decomposition of nitrates to alkali metal oxides occurs, and in the third stage the products are alkali metal oxides, silver and Co₃O₄. This paper also presents the dependence of the decomposition temperature of nitritocobaltates(III) of the silver group on the ionic radius of the outer-sphere cation.     

Thermal behavior of the polyoxometalates derived from H3PMo12O40 and H4PVMo11O40

The aim of this study is to investigate the influence of some monovalent counter-ions (NH₄ ⁺, K⁺ and Cs⁺) on thermal behavior of polyoxometalates derived from H₃PMo₁₂O₄₀ (HPM) and H₄PVMo₁₁O₄₀ (HPVM) by replacing the protons. The IR and UV-VIS-DRS spectra of some acid and neutral NH₄ ⁺, K⁺, Cs⁺ salts, which derived from HPM and HPVM, confirmed the preservation of Keggin units (KU) structure. The X-ray diffraction spectra clearly showed the presence of a cubic structure. The non-isothermal decomposition of studied polyoxometalates proceeds by a series of processes: the loss of crystallization water; the loss of O₂ accompanying with a reduction of V⁵⁺→V⁴⁺ and Mo⁶⁺→Mo⁵⁺; the loss of constitution water started at 360°C for HPVM salts and 420°C for HPM salts; the decomposition of ammonium ion over 420°C with NH₃, N² and H₂O elimination and simultaneous processes of reduction (V⁵⁺→ V⁴⁺ and Mo⁶⁺→ Mo⁵⁺ or Mo⁴⁺) associating with endothermic effects; reoxidation of Mo⁵⁺, Mo⁴⁺ and V⁴⁺with a strong exothermic effect; destruction of KU to the oxides: P₂O₅, MoO₃ and V₂O₅ and the crystallization of MoO₃. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthese,Struktur und Thermolyse von NH4[Re3Br10]

Synthesis, Structure and Thermolysis of NH₄[Re₃Br₁₀] NH₄[Re₃Br₁₀] crystallizes as dark brown single crystals upon slow cooling of a hot, saturated hydrobromic-acid solution of [Re₃Br₉(H₂O)₂] after the addition of NH₄Br. The crystal structure (monoclinic, C2/m (Nr. 12); Z = 4; a = 1461.6(7), b = 1 085.6(4), c = 1030.3(7) pm, β = 92.63(4)°, V_m = 245.9(4)cm³/mol; R = 0.097, R_w = 0.043) contains [Re₃Br₁₂]^? units that share two common edges. These chains run along [010] and are held together by NH₄⁺ ions. Each NH₄⁺ is surrounded by eight Br^? from four different chains. The first step of the thermal decomposition at 290°C is the disproportionation to ReBr₃ (ReCl₃ type), rhenium metal and (NH₄)₂[ReBr₆]. Secondly, the internal reduction of (NH₄)₂[ReBr₆] at 390°C to rhenium metal takes place.     

Incorporation of cesium ion from CsNO3 into NH4Zr2(PO4)3 studied by TG-IR spectroscopy and powder XRD

The incorporation mechanism of Cs⁺ ions from CsNO₃ into NH₄Zr₂(PO₄)₃ was studied on a mixture of CsNO₃ and NH₄Zr₂(PO₄)₃ by powder X-ray diffraction analysis and by monitoring off-gases released from the mixture upon heating with a thermogravimetry analyzer connected to an infrared spectrometer. With increasing temperature, the decomposition of CsNO₃ first started, followed by the conversion of NH₄Zr₂(PO₄)₃ to HZr₂(PO₄)₃ with the release of NH₃. At around 500°C, the Cs Zr₂(PO₄)₃ phase started to appear as a result of the H⁺/Cs⁺ ion exchange. No Cs⁺ ion loss was observed at thermal treatment temperatures of 900°C and lower.     

Mass spectra of sulfinamide derivatives and identification of their thermal decomposition products

The mass spectra of 30 sulfinamide derivatives (RSONHR', R' alkyl or p-XC₆H₄) are reported. Most of the spectra had peaks attributable to thermal decomposition products. For some compounds these were identified by pyrolysis under similar conditions to be: RSO₂NHR', RSO₂SR, RSSR and NH₂R' (in all kinds of sulfinyl amides); RSNHR' (in the case of arylsulfinyl arylamides); RSO₂C₆H₄NH₂, RSOC₆H₄NH₂ and RSC₆H₄NH₂ (in the case of arylsulfinyl arylamides of the type of X = H) The mass spectra of the three thermally stable compounds showed that there are several kinds of common fragment ions. The mass spectra of the thermally labile compounds had two groups of ions; (i) characteristic fragment ions of the intact molecules and (ii) the molecular ions of the thermal decomposition products. It was concluded that the sulfinamides give the following ions after electron impact: [M]⁺, [M ? R]⁺, [M ? R + H]⁺, [M ? SO]⁺, [RS]⁺, [NHR']⁺, [NHR' + H]⁺, [RSO]⁺, [RSO + H]⁺, [R]⁺, [R + H]⁺, [R']⁺ and [M ? OH]⁺, and that the thermal decomposition products give the following ions: [RSO₂SR]⁺, [RSSR]⁺, [M ? O]⁺, [M + O]⁺ and [RSOC₆H₄NH₂]⁺.     

Studies on the thermal decomposition of alkali metal thiosulphatobismuthates(III)

The thermal decomposition of thiosulphatobismuthates(III) of alkali metals was investigated. The general formulae of the thiosulphatobismuthates are M₃[Bi(S₂O₃)₃]·H₂O where M = Na, K, Rb or Cs, and M₂Na[Bi(S₂O₃)₃]·H₂O where M = K or Cs.Typical thermal curves for thiosulphatobismuthates(III) and the results obtained in thermal, X-ray, chemical and spectrophotometrical analyses of the decomposition products are shown. The results were used to determine three stages of the thermal decomposition. At the first stage, at about 200°C, hydrated compounds are dehydrated. At the second stage, above 200°C, there is a rapid decrease in mass which is caused by evolving sulphur dioxide; bismuth sulphide and an intermediate decomposition product are formed. At about 320°C the thermal decomposition products are bismuth sulphide and alkali metal sulphate.     

Mössbauer study of the thermal decomposition of alkali tris(oxalato)ferrates(III)

The thermal decomposition of alkali (Li,Na,K,Cs,NH₄) tris(oxalato)ferrates(III) has been studied at different temperatures up to 700°C using Mössbauer, infrared spectroscopy, and thermogravimetric techniques. The formation of different intermediates has been observed during thermal decomposition. The decomposition in these complexes starts at different temperatures, i.e., at 200°C in the case of lithium, cesium, and ammonium ferrate(III), 250°C in the case of sodium, and 270°C in the case of potassium tris(oxalato)ferrate(III). The intermediates, i.e., Fe¹¹C₂O₄, K₆Fe¹¹₂(ox)₅. and Cs₂Fe¹¹ (ox)₂(H₂O)₂, are formed during thermal decomposition of lithium, potassium, and cesium tris(oxalato)ferrates(III), respectively. In the case of sodium and ammonium tris(oxalato)ferrates(III), the decomposition occurs without reduction to the iron(II) state and leads directly to α-Fe₂O₃.     

Structures and energetics of complexation of metal ions with ammonia,water, and benzene: A computational study

Quantum chemical calculations have been performed at CCSD(T)/def2‐TZVP level to investigate the strength and nature of interactions of ammonia (NH₃), water (H₂O), and benzene (C₆H₆) with various metal ions and validated with the available experimental results. For all the considered metal ions, a preference for C₆H₆ is observed for dicationic ions whereas the monocationic ions prefer to bind with NH₃. Density Functional Theory–Symmetry Adapted Perturbation Theory (DFT‐SAPT) analysis has been employed at PBE0AC/def2‐TZVP level on these complexes (closed shell), to understand the various energy terms contributing to binding energy (BE). The DFT‐SAPT result shows that for the metal ion complexes with H₂O electrostatic component is the major contributor to the BE whereas, for C₆H₆ complexes polarization component is dominant, except in the case of alkali metal ion complexes. However, in case of NH₃ complexes, electrostatic component is dominant for s‐block metal ions, whereas, for the d and p‐block metal ion complexes both electrostatic and polarization components are important. The geometry (M⁺–N and M⁺–O distance for NH₃ and H₂O complexes respectively, and cation–π distance for C₆H₆ complexes) for the alkali and alkaline earth metal ion complexes increases down the group. Natural population analysis performed on NH₃, H₂O, and C₆H₆ complexes shows that the charge transfer to metal ions is higher in case of C₆H₆ complexes. © 2016 Wiley Periodicals, Inc.     

TG–MS–FTIR (evolved gas analysis) of kaolinite–urea intercalation complex

The products evolved during the thermal decomposition of kaolinite–urea intercalation complex were studied by using TG–FTIR–MS technique. The main gases and volatile products released during the thermal decomposition of kaolinite–urea intercalation complex are ammonia (NH₃), water (H₂O), cyanic acid (HNCO), carbon dioxide (CO₂), nitric acid (HNO₃), and biuret ((H₂NCO)₂NH). The results showed that the evolved products obtained were mainly divided into two processes: (1) the main evolved products CO₂, H₂O, NH₃, HNCO are mainly released at the temperature between 200 and 450 °C with a maximum at 355 °C; (2) up to 600 °C, the main evolved products are H₂O and CO₂ with a maximum at 575 °C. It is concluded that the thermal decomposition of the kaolinite–urea intercalation complex includes two stages: (a) thermal decomposition of urea in the intercalation complex takes place in four steps up to 450 °C; (b) the dehydroxylation of kaolinite and thermal decomposition of residual urea occurs between 500 and 600 °C with a maximum at 575 °C. The mass spectrometric analysis results are in good agreement with the infrared spectroscopic analysis of the evolved gases. These results give the evidence on the thermal decomposition products and make all explanation have the sufficient evidence. Therefore, TG–MS–IR is a powerful tool for the investigation of gas evolution from the thermal decomposition of materials and its intercalation complexes.     

Study of the thermal decomposition of cellulose-hyphan and its complexes with some transition and indium metal ions

The studied complexes formed by the chelating ion exchanger were characterized by reflectance and infrared spectrometry. The thermal degradation of pure cellulose-hyphan (CH) and its complexes with Hg²⁺, In³⁺, Cr³⁺, Mo⁴⁺ and Mn²⁺ under an atmosphere of air has been studied using thermal gravimetry (TG) and differential thermal analysis (DTG). The results showed that four different stages are accompanying the decomposition of (CH) and its complexes with the studied metals. These stages were found to be affected by the presence of the investigated metal ions. On the bases of the applicability of a non-isothermal kinetic equation it was found to be a first-order reaction with the rate of degradation,k, ranging from 8.3·10^?5 to 6.2·10^?3 for (CH) and from 1.7·10^?5 to 6.6·10^?3 s^?1 for its complexes. The activation energy,E _a, the entropy change, ΔS°, the enthalpy change, ΔH° and Gibbs free energy, ΔG° are calculated by applying the rate theory of the first-order reaction. The effect of the different central metal ions on the calculated thermodynamic parameters is discussed.     

Synthesis and characterization of solid molybdenum(VI) complexes with glycolic,mandelic and tartaric acids. Photochemistry behaviour of the glycolate molybdenum complex

The complexes (NH₄)₂[MoO₂(C₂H₂O₃)₂]·H₂O, (NH₄)₂[MoO₂(C₈H₆O₃)₂] and (NH₄)₂[MoO₃(C₄H₄O₆)]·H₂O were prepared by reaction of MoO₃ with glycolic, mandelic and tartaric acids, respectively. The complexes were characterized by elemental and thermal analysis, IR spectroscopy and X-ray diffraction. Crystals of the glycolate and tartarate complexes are orthorhombic and the mandelate complex is monoclinic. Elemental and thermal analysis data showed that the glycolate and tartarate complexes are monohydrated. Hydration water is not present in the structure of the mandelate complex. IR spectra showed COO^? is involved in coordination as well as the oxygen atom of the deprotonated hydroxyl group of the α-carbon. The glycolate molybdenum complexes with general formula M₂[MoO₂(C₂H₂O₃)₂]·nH₂O, where M is an alkali metal and n?=?1 or ½, were also prepared and characterized. Aqueous solutions of the glycolate complex become blue and mandelate and tartarate complexes change to yellow or brown when exposed to UV-radiation.     

Reduction of iodine by hydroxylamine within the pH range 0.7–3.5

The reduction of iodine by hydroxylamine within the [H⁺] range 3×10⁻¹–3×10⁻⁴ mol.L⁻¹ was first studied until completion of the reaction. In most cases, the concentration of iodine decreased monotonically. However, within a narrow range of reagent concentrations ([NH₃OH⁺]₀/[I₂]₀ ratio below 15, [H⁺] around 0.1 mol.L⁻¹, and ionic strength around 0.1 mol.L⁻¹), the [I₂] and [I₃⁻] vs. time curves showed 2 and 3 extrema, respectively. This peculiar phenomenon is discussed using a 4 reaction scheme (I₂+I⁻⇔︁I₃⁻, 2 I₂+NH₃OH⁺+H₂O→HNO₂+4 I⁻+5 H⁺, NH₃OH⁺+HNO₂→N₂O+2 H₂O+H⁺, and 2 HNO₂+2 I⁻+2 H⁺→2 NO+I₂+2 H₂O). In a flow reactor, sustained oscillations in redox potential were recorded with an extremely long period (around 24 h). The kinetics of the reaction was then investigated in the starting conditions. The proposed rate equation points out a reinforcement of the inhibition by hydrogen ions when [H⁺] is above 4×10⁻² mol.L⁻¹ at 25°C. A mechanism based on ion-transfer reactions is postulated. It involves both NH₂OH and NH₃OH⁺ as the reducing reactive species. The additional rate suppression by H⁺ at low pH would be connected to the existence of H₂OI⁺ in the reactive medium. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 785–797, 1998     

Thermal decomposition of barium oxomolybdenum(VI) oxalate

A new molybdenum(VI) oxalato complex, Ba[MoO₃(C₂O₄)]·3H₂O (BMO), was prepared and characterized by chemical analysis and infrared spectral studies. Thermal decomposition studies were made using thermogravimetry and differential thermal analysis. Dehydration reactions take place up to 280°C in three stages with loss of one half, one and a half and one mole of water per mole of BMO, respectively. Decomposition of oxalate takes place between 280 and 435°C in a single step to give BaMoO₄ as the end product, which was characterized by chemical analysis, infrared and X-ray studies. The X-ray diffraction pattern of BMO shows that it is an amorphous compound. A chain structure containing MoO₆ octahedra linked through oxygen is proposed on the basis of the infrared absorption spectrum.     

Comparative study of the synthesis of layered transition metal molybdates

Mixed metal oxides (MMOs) prepared by the mild thermal decomposition of layered double hydroxides (LDHs) differ in their reactivity on exposure to aqueous molybdate containing solutions. In this study, we investigate the reactivity of some T-Al containing MMOs (T=Co, Ni, Cu or Zn) towards the formation of layered transition metal molybdates (LTMs) possessing the general formula AT₂(OH)(MoO₄)₂·H₂O, where A=NH₄⁺, Na⁺ or K⁺. The phase selectivity of the reaction was studied with respect to the source of molybdate, the ratio of T to Mo and the reaction pH. LTMs were obtained on reaction of Cu-Al and Zn-Al containing MMOs with aqueous solutions of ammonium heptamolybdate. Rehydration of these oxides in the presence of sodium or potassium molybdate yielded a rehydrated LDH phase as the only crystalline product. The LTM products obtained by the rehydration of MMO precursors were compared with LTMs prepared by direct precipitation from the metal salts in order to study the influence of preparative route on their chemical and physical properties. Differences were noted in the composition, morphology and thermal properties of the resulting products.     

FTIR and thermal studies on gel grown neodymium tartrate crystals

The growth of neodymium tartrate crystals was achieved in silica gel by single diffusion method. Optimum conditions were established for the growth of good quality crystals. Fourier transform infrared (FT-IR) spectroscopic study indicates the presence of water molecules and tartrate ligands and suggests that tartrate ions are doubly ionised. The thermal behaviour of the material was studied using thermogravimetry (TG), differential thermal analysis (DTA), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). Thermogravimetric analysis support the suggested chemical formula of the grown crystal to be Nd₂(C₄H₄O₆)₃·7H₂O, and the presence of seven water molecules as water of hydration. It is shown that the material is thermally stable up 45 °C beyond which it decomposes through many stages till the formation of neodymium oxide (Nd₂O₃) at 995 °C. The decomposition pattern is reported to be typical of a hydrated metal tartrate.     

Crystal structures of some crystal hydrates of binary molybdates

The structures of a series of binary molybdates with the lithium cation LiM(MoO₄) · H₂O (M = K⁺, Na⁺, Rb⁺, NH ₄ ⁺ ) are analyzed and compared. Except for LiNa(MoO₄) · 2H₂O, in all other compounds the lithium cations have a tetrahedral coordination formed by the oxygen atoms of the water molecules and molybdate groups. The structure of LiNa(MoO₄) · 2H₂O was found to contain a unique coordination polyhedron of lithium, i.e., a trigonal bipyramid formed by the O atoms of the water molecules and oxo anions.     

Elektromotorisches Verhalten von Glaselektroden in flüssigem Ammoniak

Glass electrodes behaving as protodes or alkali cation electrodes in aqueous systems respond to the protonated solvent in liquid ammonia at — 38°C and can be used to measure the activity of NH₄⁺. Deviations in the response to the activity of NH₄⁺ are shown to be due to an alkali metal function (alkaline error) of the glass electrodes. The selectivity of glass electrodes for different alkali metal cations changes drastically from water to liquid ammonia.     

Some studies on thallium oxalates. I. Thermal decomposition of ammonium bisoxalatothallate(III)

Trivalent thallium is precipitated in the presence of 0.1 M HNO₃ (or 0.05 M H₂SO₄) and O.1 M NH₄NO₃ (or 0.05 M (NH₄)₂SO₄) with oxalic acid. The chemical analysis of the salt obtained correspondens to the formula, NH₄[Tl(C₂O₄)₂]·3H₂O. The thermal decomposition studies of the complex indicate the formation of the intermediates ammonium thallous oxalate (stable from 150° to 160°C) and thallous oxalate (stable up to 290°C) and the final product to be a mixture of 25% of thallous oxide and 75% of thallic oxide (stable from 450° to 650°C). The infrared absorption spectra, X-ray diffraction patterns, microscopic observations and the electrical resistance measurements are used to characterise the complex and the intermediates of its thermal decomposition.     

Was ist „Molybdänsäure”︁ oder „Polymolybdänsäure”︁?

What is “Molybdic Acid” or “Polymolybdic Acid”? According to a comparative study of the literature, supplemented by well-aimed experimental investigations and equilibrium calculations, the terms “molybdic acid” or “polymolybdic acid”, used for many substances, species, or solutions in the literature, are applicable to a species, a solution, and two solids:

• a) The monomeric molybdic acid, most probably having the formula MoO₂(OH)₂(H₂O)₂(? H₂MoO₄, aq), exists in (aqueous) solution only and never exceeds a concentration of ≈ 10^?3 M since at higher concentrations it reacts with other monomemeric molybdenum (VI) species to give anionic or cationic polymers.
• b) A concentrated (>0.1 M Mo^VI) aqueous molybdate solution of degree of acidification P = 2 (realized, e. g., by a solution of one of the Mo^VI oxides; by any molybdate solutions whose cations have been exchanged by H₃O⁺ on a cation exchanger; by suitable acidification of a molybdate solution) contains 8 H₃O⁺ and the well-known polyanion Mo₃₆O₁₁₂(H₂O)₁₆^8? exactly in the stoichiometric proportions.
• c) A glassy substance, obtained from an alkali metal salt-free solution prepared according to (b), refers to the compound (H₃O)₈[Mo₃₆O₁₁₂(H₂O)₁₆]·xH₂O, x = 25—29.
• d) A solid having the ideal composition [(H₃O)Mo₅O₁₅(OH)H₂O·H₂O]∞ consists of a polymolybdate skeleton (the well-known ?decamolybdate”? structure), in the tunnels of which H₃O⁺ and H₂O are intercalate. The structure is very unstable if only H₃O⁺ cations are present, but it is enormously stabilized by a partial exchange of H₃O⁺ by certain alkali or alkaline earth metal cations.

For the compounds MoO₃, MoO₃·H₂O, and MoO₃·2H₂O the term ?molybdic acid”? is unjustified. The commercial product ?molybdic acid, ≈85% MoO₃”? is the well-known polymolybdate (NH₄)₂O·4 MoO₃ with a layer structure of the polyanion.     

Preparation of sodium dimolybdate by the pyrolysis of sodium oxomolybdenum (VI) oxalate

Thermal studies on various oxalato complexes have been of immense interest as they yield finely divided, highly reactive oxides which are usually obtained at a much lower temperature than that required in the conventional method of preparation, i.e., heating a mixture of two or more constituents [1]. A survey of the literature reveals that the compounds having the general formula A₂[Mo₂O₅(C₂O₄)₂(H₂O)₂], where A = K⁺, NH⁺₄[2] and A = Cs⁺ [3], have been prepared and their thermal decomposition is studied, but no such information is available regarding the preparation and characterisation of Na₂[Mo₂O₅(C₂O₄)₂(H₂O)₂] (SMO), which forms the subject of study of this paper. Sodium dimolybdate (Na₂Mo₂O₇), the decomposition product of SMO, is obtained at 280°C, a temperature much lower than that required in the conventional method of preparation of heating a mixture of Na₂MoO₄ and MoO₃ [4].