Thermal investigations of nickel–zinc ferrites formation from malate coordination compounds

Nickel–zinc ferrites have been synthesized via thermal decomposition of polynuclear coordination compounds containing as ligand the anion of malic acid, namely (NH₄)[Fe₂NixZn_1–x(C₄H₄O₅)(OH)₃]·nH₂O (x =0.25, 0.5 and 0.75, n=3 and 5). A comparison between the thermal behaviour of the studied polynuclear coordination compounds is inferred. Fe₂NixZn_1–xO₄ (n=0.25, 0.5 and 0.75) ferrites with mean particle sizes of 65–85 Å and free from other phases are formed after a heating treatment of only one hour at 500°C.     

Non-Conventional Methods for Obtaining Hexaferrites Thermal Analysis of Some Precursors

Bd. Republicii, Nr. 13, sector 2, Bucharest The thermal behaviour of the polynuclear coordination compounds [Fe_12?xSr(malic)_19?1.5x]·18H₂O and [Fe_12?xSr(gluc)_19?1.5x]·20H₂O precursors of strontium hexaferrite was investigated, and a decomposition mechanism is proposed. A pure hexaferrite with a mean crystallite size value of about 250 Å was obtained after 5 h calcination at 800°C of the gluconic precursor (x=1.5).     

Iron,nickel and zinc malates coordination compounds cynthesis,characterization and thermal behaviour

The coordinations compounds (NH₄)[Fe(C₄H₄O₅)(OH)₂]·0.5H₂O, [Ni(C₄H₄O₅)]·3H₂O and [Zn(C₄H₄O₅)]·5H₂O were synthesized by a precipitation method and characterized by chemical analysis, spectral (IR, UV-VIS) and magnetical investigations. In the range 50-600°C stepped thermal decompositions occur with formation of anhydrous malates, malonates, oxoacetates (iron and nickel compounds) and hydroxocarbonate (Zn compound) as intermediates observed by FT-IR spectroscopy. α-Fe₂O₃, NiO and ZnO constitute the final decomposition products. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal analysis of some polynuclear coordination compounds

The thermal behaviour of five polynuclear coordination compounds containing tartaric anion as ligand, namely (NH₄)₃[LnFe(C₄O₆H₄)₃(OH)₃] (Ln=La and Eu), (NH₄)₂[PrFe(C₄O₆H₄)₃(OH)₂] and (NH₄)[LnFe(C₄O₆H₄)₃(OH)]·3H₂O (Ln=Nd and Gd) was investigated. The reaction progress was studied by TG/DTA and FTIR measurements. Oxalates and oxocarbonates were identified as intermediates. In the case of Ln=La, Nd, Pr, Eu and Gd, pure LnFeO₃ was obtained as final decomposition product. The thermal decomposition of Eu-Fe compound, leads to a mixture of mixed (ortho-ferrite (EuFeO₃) and garnet (Eu₃Fe₅O₁₂)) and simple oxides (Eu₂O₃ and α-Fe₂O₃).     

Synthesis,Characterization and Thermal Decompositions Studies of Some Malates Coordination CompoundsI. iron nickel compounds

The thermal behaviour of three coordination compounds, potential precursors of nickel ferrite [Fe₂Ni(C₄H₄O₅)_2.5(OH)₂]NO₃·5H₂O,[Fe₂Ni(C₄H₈O₃N₂)₄](NO₃)₈·24H₂O and (NH₄)[Fe₂Ni(C₄H₄O₅)₃(OH)₃]·3H₂O has been investigated to evaluate their suitability as precursors for nickel ferrite. For a complete and reliable assignment of the thermal transformations, the isolable solid intermediates and end products were characterized by IR, X-ray diffraction and Mössbauer investigations. A decomposition scheme is proposed.     

Synthesis of cis-Tetrabromobispyridinemolybdates(III) and the crystal structure of cis-(NH4)[MoBr4py2] · ⅓3 H2O (py = pyridine)

The reaction between (NH₄)[MoBr₅ · H₂O] and pyridine in acetonitrile (CH₃CN) at room temperature results in the mixture of cis- and trans-(pyH)[MoBr₄py₂] which can be separated on the basis of solubility. cis-M[MoBr₄py₂] · ? H₂O (M = NH₄⁺, Rb⁺, Cs⁺), cis-(bipyH)[MoBr₄py₂] (bipy = 2,2′-bipyridil) and cis-(PPh₄)[MoBr₄py₂], were prepared from cis-(pyH)[MoBr₄py₂]. At the temperature of boiling acetonitrile irreversible cis to trans isomerisation takes place. Bromine oxydizes cis isomers at room temperature to trans-MoBr₄py₂. The compounds were characterised by chemical analysis, infrared, UV-VIS spectroscopy, conductivity measurements and powder diffraction. The crystal structure of cis-(NH₄)[MoBr₄py₂] · ? H₂O has been determined: rhombohedral, R3c, (No. 161), a = 15.809(3) Å, β = 112.79(2)°, Z = 6, D_C = 2.29, D_O = 2.27(3) g/cm³, V = 2 601(1) ų, R₁ = 0.046, R_w = 0.068. Average Mo? Br and Mo? N(pyridine) distances within the anion are 2.58(2) and 2.20(2) Å. cis-Rb[MoBr₄py₂] · ? H₂O and cis-Cs[MoBr₄py₂] · ? H₂O are isostructural with cis-(NH₄)[MoBr₄py₂] · ? H₂O.     

TG,DTA, FTIR and Raman spectral analysis of Zna/Mgb ammonium sulfate mixed crystals

To understand the structural and thermal properties of the mixed crystals, thermogravimetric (TG) and differential thermal analysis (DTA), and FTIR and Raman spectral studies were carried out for the mixed crystals of Zn_a/Mg_b ammonium sulfate of composition namely 'a' (fraction by mass of salt Zn[NH₄]₂[SO₄]₂·6H₂O to the total salt (both Zn[NH₄]₂[SO₄]₂·6H₂O, Mg[NH₄]₂[SO₄]₂·6H₂O or it can be explained as Zn_aMg_b[NH₄]₂[SO₄]₂·6H₂O, a + b =1), and a = 0.1, 0.25, 0.333, 0.5, 0.666, 0.75 and 0.9 grown by a solution technique. From the correlation and analysis of the results obtained for the various crystals, the desolvation, decomposition, crystalline transition phenomena were identified. By close comparison of the endotherms, obtained for the various crystals, it was found that isomorphous substitution takes place in the crystals. Up to 0.5, Zn²⁺ ion replaces isomorphous Mg²⁺ ions in the lattice sites of Mg[NH₄]₂[SO₄]₂·6H₂O and above 0.5, Mg²⁺ ions occupies the Zn²⁺ ion in the lattice sites of Zn[NH₄]₂[SO₄]₂·6H₂O. Both crystals belong to monoclinic system with P 2(1)/a symmetry. The vibrations of NH₄ ⁺ ion, SO₄ ^2- ion, the complex [Mg(OH₂)₆]²⁺ the complex [Zn(OH₂)₆]²⁺ and the three different water molecules are identified. The linear distortion of SO₄ ^2- ion is found to be greater than its angular distortion, while the NH₄ ⁺ ion has suffered more angular distortion. The possibility of free rotation of the NH₄ ⁺ ion is ruled out.     

Synthesis, structure, and properties of M[VO2(XO4)(H2O)2] · H2O (X = S, M = K, Rb, NH4, Tl; X = Se, M = K, Rb, NH4)

Keeping of MVO(XO₄)₂ under saturated vapor pressure at room temperature resulted in the synthesis of a number of isostructural complexes M[VO₂(XO₄)(H₂O)₂] · H₂O, where X = S, M = K, Rb, NH₄, Tl and X = Se, M = K, Rb, NH₄. The conclusion about the isostructural nature of the synthesized sulfate and selenate compounds was based on X-ray diffraction and vibrational spectroscopy data. Characteristic features of the thermal decomposition of M[VO₂(XO₄)(H₂O)₂] · H₂O on heating in air were identified. It was shown that K[VO₂(SeO₄)(H₂O)₂] · H₂O tends to undergo spontaneous dehydration under ambient conditions to give the monohydrate K[VO₂(SeO₄)(H₂O)].     

Thermal decomposition of Cu(II) complexes with salicylaldehyde S-methyl thiosemicarbazone

The thermal decomposition of copper(II) complexes with salicylaldehyde S-methylthiosemicarbazone of general formula Cu(HL)X·nH₂O (X=Py+NO₃, NCS, 0.5SO₄) and [Cu(L)NH₃]·H₂O was investigated in air atmosphere in the interval from room temperature to 1000°C. Decomposition of the complexes occurred in several successive endothermic and exothermic processes, and the residue was in all cases CuO.     

Thermal analysis of some polynuclear coordination compounds as precursors of iron garnets (M3Fe5O12, M=Y3+ or Er3+)

The thermal behaviour of four coordination compounds (NH₄)₆[Y₃Fe₅(C₄O₅H₄)₆(C₄O₅H₃)₆]·12H₂O, (NH₄)₆[Y₃Fe₅(C₆O₇H₁₀)₆(C₆O₇H₉)₆]·8H₂O, (NH₄)₆[Er₃Fe₅(C₄O₅H₄)₆(C₄O₅H₃)₆]·10H₂O and (NH₄)₆[Er₃Fe₅(C₄O₆H₄)₆(C₄O₆H₃)₆]·22H₂O has been studied to evaluate their suitability for garnet synthesis. The thermal decomposition and the phase composition of the resulted decomposition compounds are influenced by the nature of metallic cations (yttrium-iron or erbium-iron) and ligand anions (malate or gluconate).     

Influence of precursor on the thermally Induced synthesis dysprosium manganite with perovskite structure

The thermal behaviour of two coordination compounds [MnDy(malic)3]· 5H₂O and [MnDy(gluconic)3]·12H₂O has been studied to evaluate their suitability for dysprosium manganese perovskite ;synthesis. A decomposition scheme is proposed leading to perovskites with orthorhombic (malic precursor) and hexagonal (gluconic precursor) structures which were obtained after a heating treatment of 4 h at 1000°C with one-hour plateau at 500°C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Investigation of thermal properties of double complex salts [M(NH3)5Br][AuBr4]2·nH2O, M?=?Rh, Ir

Novel double complex salts [M(NH₃)₅Br][AuBr₄]₂·nH₂O, M?=?Rh, Ir, have been synthesized and examined. The processes of thermal decomposition of the compounds in inert and reductive atmospheres have been studied and intermediate products identified. Simultaneous thermal analysis with parallel mass-spectrometric analysis of evolved gases (STA-EGA) has been employed for identification of main gaseous products of thermolysis in inert atmosphere. It has been revealed that the final products of decomposition in inert or reductive atmospheres are fine powders of gold and the corresponding platinum metal with sizes of crystallites 4?C40?nm. The possibility of preparation of the metastable solid solution Au_0.05Ir_0.95 on thermolysis of [Ir(NH₃)₅Br][AuBr₄]₂·H₂O in inert atmosphere has been demonstrated.     

Thermal Decomposition and Dehydration Kinetics of Tetra(piperidinium) Octamolybdate Tetrahydrate in Air

Thermal decomposition of tetra(piperidinium) octamolybdate tetrahydrate, [C₅H₁₀NH₂]₄[Mo₈O₂₆]·4H₂O, was investigated in air by means of TG‐DTG/DTA, DSC, TG‐IR and SEM. TG‐DTG/DTA curves showed that the decomposition proceeded through three well‐defined steps with DTA peaks closely corresponding to mass loss obtained. Kinetics analysis of its dehydration step was performed under non‐isothermal conditions. The dehydration activation energy was calculated through Friedman and Flynn‐Wall‐Ozawa (FWO) methods, and the best‐fit dehydration kinetic model function was estimated through the multiple linear regression method. The activation energy for the dehydration step of [C₅H₁₀NH₂]₄[Mo₈O₂₆]·4H₂O was 139.7 kJ/mol. The solid particles became smaller accompanied by the thermal decomposition of the title compound.     

On the reduction of Cr3+ during the thermal decomposition of fluorochromates(III) with nitrogen containing cations

The thermal decomposition of [CO(NH₂)₂H]CrF₆·H₂O, (C₃N₆H₈)CrF₅·H₂O and the solid state reaction of CrF₃ and melamine are investigated under non-reciprocal quasi-static conditions and compared with the thermal behaviour of other fluorochromates(III) ([Cr(NH₃)₆]CrF₆, (NH₄)₃CrF and [C(NH₂)₃]₃CrF₆). The comparison of the results shows that the amount of chromium(II) in the final product is determined by the thermal stability and consequently by the decomposition temperature of the intermediates. Neither bonding properties in the starting materials nor the absolute amount of generated NH₃ influence the composition of the final product.     

Thermal stability of new zinc acetate-based complex compounds

New zinc acetate based complex compounds (of general formula Zn(CH₃COO)₂·1?2L·nH₂O) containing one or two molecules of urea, thiourea, coffeine and phenazone were prepared namely: Zn(CH₃COO)₂·2.5H₂O, Zn(CH₃COO)₂·2u·0.5H₂O, Zn(CH₃COO)₂·tu·0.5H₂O, Zn(CH₃COO)₂·2tu, Zn(CH₃COO)₂·cof·2.5H₂O, Zn(CH₃COO)₂·2cof·3.5H₂O, Zn(CH₃COO)₂·2phen·1.5H₂O. The compounds were characterized by IR spectroscopy, chemical analysis and thermal analysis. Thermal analysis showed that no changes in crystallographic modifications of the compounds take place during (heating in nitrogen before) the thermal decompositions. The temperature interval of the stability of the prepared compounds were determined. It was found that the thermal decomposition of hydrated compounds starts by the release of water molecules. During the thermal decomposition of anhydrous compounds in nitrogen the release of organic ligands take place followed by the decomposition of the acetate anion. Zinc oxide and metallic zinc were found as final products of the thermal decomposition of the zinc acetate based complex compounds studied. Carbon dioxide and acetone were detected in the gaseous products of the decomposition of the compounds if ZnO is formed. Carbon monoxide and acetaldehyde were detected in the gaseous products of the decomposition, if metallic Zn is formed. It is supposed that ZnO and Zn resulting from Zn acetate complex compounds here studied, possess different degree of structural disorder. Annealing takes place by further heating above 600°C.     

Research on thermal decomposition of trinitrophloroglucinol salts by DSC, TG and DVST

The thermal decomposition of the four nitrogen-rich salts of ammonia (NH₄), aminoguanidine (AG), carbohydrazide (CHZ) and 5-aminotetrazo (ATZ) based on trinitrophloroglucinol (H₃TNPG) was investigated using the differential scanning calorimetry (DSC), thermogravity (TG), and dynamic vacuum stability test (DVST). DSC and TG methods research the complete decomposition, while DVST method researches the very early reaction stage. The peak temperatures of DSC curves are consistent with the temperatures of maximum mass loss rates of TG curves. The apparent activation energies of these H₃TNPG-based salts obtained by DSC and DVST have the same regularity, i.e., (ATZ)(H₂TNPG)·2H₂O < (CHZ)(HTNPG)·0.5H₂O < NH₄(H₂TNPG) < (AG)(H₂TNPG). The thermal stability order is (ATZ)(H₂TNPG)·2H₂O < (CHZ)(HTNPG)·0.5H₂O < (AG)(H₂TNPG) < NH₄(H₂TNPG), which was evaluated by DVST according to the evolved gas amount of thermal decomposition. DVST can monitor the real-time temperature and pressure changes caused by thermal decomposition, dehydration, phase transition and secondary reaction, and also evaluate the thermal stability and kinetics.      

1,4‐Bis{[hydroxy(phenyl)phosphoryl]methyl}piperazine‐1,4‐diium tetrachloridocadmate(II) dihydrate and the cobaltate(II) analogue

The reaction of aminophosphinic acid with CdCl₂·2.5H₂O or CoCl₂·6H₂O in concentrated hydrochloric acid yielded the isostructural compounds 1,4‐bis{[hydroxy(phenyl)phosphoryl]methyl}piperazine‐1,4‐diium tetrachloridocadmate(II) dihydrate, (C₁₈H₂₆N₂O₄P₂)[CdCl₄]·2H₂O, (I), and 1,4‐bis{[hydroxy(phenyl)phosphoryl]methyl}piperazine‐1,4‐diium tetrachloridocobaltate(II) dihydrate, (C₁₈H₂₆N₂O₄P₂)[CoCl₄]·2H₂O, (II). The asymmetric unit of each contains two half dications, both located on crystallographic centres of inversion, a tetrachloridometallate(II) dianion and two solvent water molecules. The residues are linked into two‐dimensional layers in the ab plane by O—H...O hydrogen bonds.     

Thermochemistry of the Decomposition of Some Cobalt Compounds

Differential scanning calorimetry (DSC) was used to determine the molar enthalpies of dehydration and decomposition of CoC₂O₄·2H₂O, Co(HCOO)₂·2H₂O and [Co(NH₃)₆]₂(C₂O₄)₃·4H₂O. The first stage of dissociation of each compound is a single-step dehydration both in air and argon atmospheres. The next stages are decomposition processes influenced by experimental parameters. The enthalpies of dehydration and decomposition vary from compound to compound in each atmosphere. The obtained data have been related to the macromechanisms proposed for the thermal decomposition and the parallel-consecutive decomposition-oxidation processes. This revised version was published online in August 2006 with corrections to the Cover Date.     

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.     

Tetranitratogoldsäure, (H5O2)[Au(NO3)4]·H2O: Synthese,Kristallstruktur und thermisches Verhalten des ersten sauren Nitrates des Goldes

Tetranitratogold(III) Acid, (H₅O₂)[Au(NO₃)₄]·H₂O: Synthesis, Crystal Structure, and Thermal Behaviour of the First Acidic Nitrate of Gold Yellow single crystals of (H₅O₂)[Au(NO₃)₄]·H₂O grow upon cooling of a solution of Au(OH)₃ in conc. nitric acid. The crystal structure contains (monoclinic, C2/c, Z = 4, a = 1214.5(2), b = 854.4(1), c = 1225.7(2) pm, β = 117.75(1)°, R_all = 0.0331) the Au³⁺ ion in coordination of four monodentate NO₃^— ligands. The [Au(NO₃)₄]^— units are linked by H₅O₂⁺‐ions. Significant hydrogen bonding is observed in the crystal structure between the H₅O₂⁺ ions and the H₂O molecules. The thermal analysis reveals a five step decomposition leading to elemental gold.