Anhydrous Compounds Research Articles

Thermal features and behaviour of 4-aminopyridinium salts of planar inorganic metal(II) 1,2-dithiooxalato- 5', 5 complexes, with formula (HC 5H 6N 2) 2[M(S 2C 2O 2) 2]·2H 2O (where M is Ni II, Pd II and Pt II)

Thermal decompositions of three 4-aminopyridinium salts of square-planar inorganic metal(II) 1,2-dithiooxalato- S,S' complexes, (HC 5H 6N 2) 2[M(S 2C 2O 2) 2] · 2H 2O where M is Ni(II), Pd(II) and Pt(II) (hereafter abbreviated as NIDT4AP, PDDT4AP and PTDT4AP, respectively) have been studied by thermogravimetry (TG and DTG) and differential thermal analysis (DTA) under argon-oxygen and argon atmospheres. Thermoanalytical data show that the surrounding atmosphere influences the thermal decomposition processes as well as the final products. In argon-oxygen atmosphere, the final residues were identified as a mixture of nickel sulphides and oxides for NIDT4AP, metallic palladium and palladium oxide for PDDT4AP, and platinum(0) for PTDT4AP. Thermal decompositions in an inert atmosphere yielded nickel(II) sulphide for NIDT4AP, a mixture of Pd/PdS for PDDT4AP, and metallic platinum for PTDT4AP. The final decomposition products were identified by elemental analysis and the X-ray powder diffraction technique. No other stable intermediate products, except the corresponding anhydrous compounds, were found during the thermal decomposition owing to the complexity and the overlap of the processes in oxidative and inert atmospheres.

Thermal properties of neodymium hydrazidocarbonate trihydrate

The thermal properties of lanthanide hydrazidocarbonates were studied in an inert atmosphere by selecting neodymium hydrazidocarbonate trihydrate, Nd(N 2H 3COO) 3·3H 2O, as a model substance for the essentially similar thermal behaviour of hydrazidocarbonates of all the lanthanides except promethium. Neodymium hydrazidocarbonate trihydrate cannot be converted into a pure anhydrous compound by heat treatment because the dehydration of the sample is accompanied by partial decomposition of the other part of the molecule, i.e. the hydrazidocarbonato groups. The decomposition finally proceeds through some intermediates to a mixture of neodymium oxide and amorphous carbon, and finally at 1450°C, to neodymium oxide carbide, Nd 2C 2O 2.

Formation of Pt(III) complexes in irradiated potassium tetranitroplatinate(II): a single crystal ESR study

X-irradiation of single crystals of K 2[Pt(NO 2)] and of K 2[Pt(NO 2) 4]·2H 2O leads to the formation of Pt(III) complexes which have been studied by EPR at 77 K. The crystal structure of the hydrated compound has been determined in order to interpret the orientation of the g and 195Pt hyperfine tensors and to reassign the powder spectrum previously attributed to this compound. The nature of the trapped species is shown to be dependent upon the presence of water molecules: one of the two Pt(III) complexes formed in the hydrated crystal probably results from oxidation of the original molecule by the radiogenic OH · radical whereas, for the second species, the water molecule seems only to participate in the stabilization of the Pt(III) complex. For the anhydrous compound this stabilizing effect is probably assured by a distant NO 2 group.

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.

Magnetic properties of green dioptase CuSiO3H2O and of black dioptase CuSiO3, and magnetic structure of black dioptase

The rhombohedral (R 3 ) compounds green dioptase, CuSiO 3 H 2 O, and black dioptase, CuSiO 3 , are both antiferromagnetic. Their Néel temperatures are respectively near 50 and 110 K. The magnetic structure of the anhydrous compound has been studied by powder neutron diffraction. The magnetic moment of Cu is of order 0.5 μ B .

Ultrasonic propagation through hydrating cements

Hydraulic cements develop mechanical strength and low permeability as a result of hydration, which involves chemical reactions between water and the anhydrous compounds present in the cement. Solid hydration products form both at the surfaces of the cement particles and in the pore space by nucleation and aggregation. As a result, the solid phase becomes highly connected and the material transforms from a viscous suspension of irregularly-shaped cement particles into a porous elastic solid with non-vanishing bulk and shear moduli. This transition to an interconnected solid phase is an example of a percolation transition. In this paper, measurements of the velocity of ultrasonic longitudinal and shear waves in ordinary Portland cement undergoing hydration are reported. The cement slurries were prepared in accordance with the American petroleum Institute (API) specification for class G oil-well cement with various additives. After the time at which the cement becomes interconnected, the effective bulk and shear moduli are found to be linearly related and the effective Poisson's ratio is observed to decrease from the value of 0.5, characteristic of a fluid, to values characteristic of a porous elastic solid.

Crystal structures of 2-(2-methoxyphenyl) perimidine and its hemihydrate

The crystal structures of the title compound and that of its hemihydrate have been determined. The anhydrous compound is roughly planar due to an intramolecular hydrogen bond (IMHB). The orange color can be related to its planarity and to the greater degree of overlapping between the perimidine and the phenyl group than in the hemihydrate. The yellow hemihydrate is not planar and the water molecule joins through O-H⋯N hydrogen bonds two molecules related by a crystallographic twofold axis. In solution the compound behaves like the anhydrous form.

Structural Characterization and Ion Conductivity of MCa<sub>2</sub>NaNb<sub>4</sub>O<sub>13</sub> (M=Rb, Na) with Four Units of Perovskite Layer

Layered perovskite, RbCa2NaNb4O13, with four units of perovskite layer was synthesized by solid state reaction. A sodium ion-exchanged compound, NaCa2NaNb4O13⋅1.7H2O, was also synthesized by ion-exchange reaction of a rubidium compound with NaNO3 molten salt. The anhydrous sodium ion-exchanged compound was stable in the temperature range from 350 to 600°C in an ambient atmosphere. The crystal structures of the three materials were determined using the Rietveld method by powder XRD data. The most reliable solutions were obtained for the structural model assuming that the site for a large cation within the perovskite layer, corresponding to the A site for an ideal perovskite, is occupied by the mixed species with the atomic ratio of Ca:Na=2/3:1/3. The structures of these compounds are substantially the same as those of MLaNb2O7 (M=Rb, Na) except for the thickness of the perovskite layer. A fairly high ion conductivity attributed to the interlayer cation was observed at high temperatures for the sodium compound.

Melting and glass transitions of low molecular weight carbohydrates

Glass-transition temperatures at various water contents ( T g) and in maximally freeze-concentrated solutions ( T′ g), fusion temperatures (melting points, T f), and heats of fusion (Δ H f) were determined for pentoses, hexoses, disaccharides, and alditols, using differential scanning calorimetry. The T g and T′ g values of the anhydrous compounds increased in the order pentoses < hexoses < disaccharides. The T g values of the alditols were lower than those of the corresponding sugars. Compounds with high T f/ T g ratios had high Δ H f values and showed rapid crystallisation. The T g and T′ g values allowed the prediction of T g as a function of the water content and of the concentration of the maximally freeze-concentrated matrices ( C′ g). The C′ g concentration was ∼ 80% (w/w) for each carbohydrate. The results can be used to evaluate the physical stability of various carbohydrates at various water contents and in freeze-concentrated solutions.

Preparation and characterization of potassium, rubidium and ammonium tetrachlorouranate(III) trihydrates

The synthesis and characterization of a new series of hydrated uranium(III) complex chlorides of the general formula M 1UCl 4-3H 2O (M 1K, Rb or NH 4) are reported. The compounds crystallize in the monoclinic system. Unit cell parameters were determined from X-ray powder diffraction data. The magnetic susceptibilities of the complex chlorides were measured by the Faraday method in the 4.2–300 K range. The compounds exhibit Curie-Weiss paramagnetism in the 100–300 K range, with the derived effective magnetic moments ranging from 3.57μ B to 3.71μ B. Solid state electronic and IR spectra were recorded in the 4000–30 000 and 80–4000 cm −1 ranges, respectively and discussed. Non-static high vacuum thermal dehydrations enabled us to obtain the anhydrous compounds KUCl 4, RbUCl 4 and UCl 3.

Thermal behaviour and properties of n-alkylammonium decavanadates

The thermal behaviour of three n-alkylammonium decavanadates with the general formula [(C n H 2 n+1 )NH 3IV 10O 28]·2H 2O where n = 4−6, has been studied by thermogravimetry (TG and DTG) and differential thermal analysis (DTA) under argon-oxygen and argon atmospheres from room temperature to 600°C. The surrounding atmosphere is an important factor which significantly influences the course of the decomposition reaction and the final products. In an argon-oxygen atmosphere the compounds lose two water molecules during a first endothermic step to give a stable anhydrous compound. A relationship has been found between the density values of the compounds and the dehydration temperature range. The anhydrous compounds decompose via several oxidative exothermic processes to give vanadium(V) oxide. No other stable products were found during the thermal decomposition owing to the overlap of these last oxidative processes. The thermal decompositions in an argon atmosphere begin with a similar dehydration step for the three compounds followed by a progressive weight loss. The final products at 600°C in an inert atmosphere were identified by X-ray powder diffraction data as mixtures of vanadium(IV) and vanadiumd(III) oxides. The essential thermal features, as well as the influence of the crystal structure of the n-alkylammonium decavanadates on their thermal behaviour, are also reviewed and discussed.

A thermal and mass spectrometric study of synthetic johannite [Cu(UO 2) 2(SO 4) 2(OH) 2] · 8H 2O

The course of the thermal decomposition of synthetic johannite, [Cu(UO 2) 2(SO 4) 2-(OH) 2· 8H 2O, was investigated by means of simultaneous TG-DTA-MS (thermogravimetry-differential thermal analysis-mass spectrometry). The dehydration and dehydroxylation processes (60–450°C) fall into four stages, the temperatures of which are influenced by the transport phenomena. Firstly, the four water molecules not coordinated by Cu 2+ cations are released, followed by release of the water molecules (in two steps) that are coordinated by Cu 2+ cations. Then, dehydroxylation takes place which may partly overlap with the last stage of dehydration. Further heating of the fully anhydrous compound results in a release of small amounts of oxygen at approx. 490 and 520°C, accompanied by corresponding exotherms on the DTA curve. This suggests the formation of new crystalline phases such as α-UO 2SO 4, β-UO 2SO 4 and UO 3− x . Decomposition of the anhydrous compound (CuO·2UO 3·2SO 3 or CuO+2UO 2SO 4) is characterized by the evolution of SO 3 (in two steps) and oxygen. Small exotherms at 655 and 688°C in argon and air, respectively, mark the onset of SO 3 evolution and can be assigned to the formation of crystalline CuU 3O 10. The presence of oxygen, formed both in the course of the decomposition reaction and as a result of SO 3 dissociation, causes the inhibitive influence of the oxygen content in the atmosphere over the sample on the course of decomposition.

Potential energy maps and H + conduction mechanism in HTaWO 6· xH 2O pyrochlore

Least-energy paths of proton in the structures of HTaWO 6 and HTaWO 6 ·H 2 O have been calculated by the Born model of crystal energy. The atomic charge on O and the repulsive parameters are fitted to reproduce the equilibrium crystal structure of the pyrochlore KNbWO 6 , obtaining z o =−0.70 e . Maps of H + potential energy in the anhydrous compound show that proton hopping occurs between adjacent H sites along edges of (Ta, W)O 6 coordination octahedra, with a theoretical activation energy of 0.60 eV in good agreement with the experimental value (0.66 eV). In the hydrated compound the proton transfer occurs by a similar mechanism, excluding an active role of water molecules. The small experimental activation energy observed in the latter case is probably due to surface conduction induced by humidity at grain boundaries.

Preparation and study of amino acid ( DL-leucine, L-isoleucine, L-histidine) Schiff bases with ethyl-α-ketocyclopentylcarboxylate and the corresponding copper( II) complexes

Amino acid Schiff bases with ester function K(Rleu)·2H 2O ( 1), K(Rile)·2H 2O ( 2), K(Rhis)·H 2O ( 3) (Rleu, Rile and Rhis represent the Schiff base of DL-leucine, L-isoleucine and L-histidine, and ethyl-α-ketocyclopentylcarboxylate) were synthesized. Compounds 1, 2 and 3 were characterized by 1H NMR spectroscopy. The copper(II) complexes, Cu(Rleu′)·H 2O ( 4), Cu[Rile′]·H 2O ( 5) andCu(Rhis′)·2H 2O ( 6), were obtained with the N-deprotonated Schiff bases (Rleu′, Rile′ and Rhis′). The COO stretching bands in their IR spectra suggest that the carboxylate acts as a monodentate group when binding with copper. The temperature dependence of the susceptibility for 6 may be fit to the Curie-Weiss expression χ=O.32/(T-26.2) emu mol −1 K −1 The dehydration process of 6 leads to the anhydrous compound, enthalpy (53±2kJ mol −1) and activation energy (82±5 kJ mol −1).

Influence of the coordination water on the after effects of the K-capture in57Co doped FeSO4×H2O (x=0,1,4,7)

Emission Mossbauer spectroscopy is used to investigate the physico-chemical state of57Fe atoms generated by57Co2+ clectron capture in57Co: FeSO4xH2O (x=0,1,4,7). The spectra of all the hydrates show at least three main components, the normal bivalent state, Fe2+(N), an aliovalent state, Fe3+, and one (or several) anomalous ferrous species in which the coordination sphere has been perturbated by the self-radiolysis. No Fe3+ is observed in the anhydrous compound whereas the intensity of this component increases as a function of the hydration number, reaching a saturation value of 36% for x=4 and 7.

Comparative studies on the thermal decomposition of M[M(C 2O 4) 2] · xH 2O ( x = 4 for M = Mn(II), Co(II), Zn(II); x = 5 for M = Ni(II); x = 6 for M = Cd(II) and x = 1 for M = Sn(II))

The study reveals that the thermal decomposition of most of the complexes M[M-(C 2O 4) 2] · xH 2O (where x = 4 for M = Mn, Co or Zn; x = 5 for M = Ni; x = 6 for M = Cd; and x = 1 for M = Sn) gives the anhydrous compound which on exposure to humid atmosphere is rehydrated to the original form. In air, the metal oxides were formed directly as a solid decomposition product and in nitrogen metal oxides were formed through the formation of an intermediate mixture of metal or metal oxide and metal oxalate. The evolved CO(g) exerted some additional effects in the decomposition of oxalates and the fused metal oxides had a profound effect on the decomposition of the intermediate metal oxalates. The kinetic parameters for the dehydration and decomposition steps varied according to the atmosphere and different values were obtained for the same step depending on the method applied. Variations were observed in the values calculated from thermogravimetric and differential scanning calorimetric curves.

F element croconates 1. Lanthanide croconates — synthesis, crystal structure and thermal behaviour

Lanthanide croconates free of alkaline elements have been prepared by using croconic acid or triethanolammonium croconate. They are divided into two families: 1-Ln: [Ln(H 2O) 5] 2(C 5O 5) 3·4H 2O with Ln(III)Ce, Pr, Nd, Sm, Eu, Gd; 2-Ln: [Ln(H 2O) 6] 2(C 5O 5) 3·3H 2O with Ln(III)Tb, Dy, Ho, Er, Yb. In the general conditions used to synthesize such complexes, lanthanum, lutetium and yttrium belong neither to the family 1-Ln nor to the family 2-Ln. In the presence of oxygen and exposed to daylight the latter elements induce, after a few days, a degradation of the croconate ligand leading to oxalate complexes and to another phase still unknown. A possible hypothesis is presented. A structural study has been performed on a single-crystal representative on each family: Pr for 1-Ln, Er for 2-Ln. The first family crystallizes in the orthorhombic system, space group Pccn, while the second one crystallizes in the triclinic system, space group P1. The salient feature of both structures consists of discrete, neutral, dinuclear entities: [Ln(H 2O) x ] 2(C 5O 5) 3, with x=5 for 1-Ln and x=6 for 2-Ln. However, these entities differ markedly from one family to the other by the coordination mode of the croconate ligand. For 1-Ln the two independent croconates are either chelating or bis-chelating while for 2-Ln the three independent croconates are monodentate and transmonodentate. Between the two structures, a modification of the lanthanide coordination number takes place: 9 for Pr as a distorted trigonal tricapped prism, 8 for Er (Er1 and Er2) as a deformed antisquare prism. The crystal structure is assured, in both cases, by hydrogen bonding and van der Waals interactions between stacked croconate planes. Free water molecules are localized in tunnels. Dehydration of lanthanide croconates of each family takes place in a single step around 90 to 150 °C; anhydrous compounds are stable. The decomposition of the croconate ligand proceeds via oxycarbonate according to the considered lanthanide. It starts around 310 °C, and constant weight is achieved at a variable temperature up to 700 °C, leading to the corresponding oxides. An endotherm is found for the dehydration, a strong exotherm for the croconate decomposition.

Preparation and characterization of dinuclear copper(II) complexes containing the [Cu 2(μ-OAc) 2] 2+ core

Treatment of an aqueous slurry of known Cu 2(OH) 2(bpy) 2(ClO 4) 2 ( 1) with an excess of MeCOOH led to rapid formation of the blue complex [Cu 2(O 2CMe) 2(H 2O) 2(bpy) 2](ClO 4) 2·H 2O ( 3). Complex 3 has also been prepared by slow crystallization from an H 2O/MeCOOH reaction mixture containing the polymeric compound [Cu 4(O 2CMe) 8 (bpy) 2] n ( 5), bpy and NaClO 4. A similar reaction system containing a lesser amount of H 2O led to fast precipitation of the anhydrous compound [Cu 2(O 2CMe) 2(OClO 3) 2(bpy) 2] ( 4). The transformation of 1 to 3 is reversible; treatment of 3 with neat H 2O led to high-yield isolation of 1. Using a significantly shorter reaction time and a smaller volume of H 2O, the procedure yielded the known complex [Cu 2(OH)(H 2O)(O 2CMe)(bpy) 2](ClO 4) 2 ( 2). Similarly, complex 4 can be transformed to 2 in good yield. Complex 3 crystallizes in the monoclinic space group P2 1/ a with (at - 172°C) a = 17.037(3), b = 9.743(2), c = 18.357(4) Å, β = 98.19(5)°, Z = 4 and V = 3016.05 Å 3. A total of 3651 unique data with F > 2.33σ( F) were refined to values of conventional indices R ( R w) of 7.89 (8.74)%. Complex 4 crystallizes in the monoclinic space group C2/ c with (at - 172°C) a = 11.555(4), b = 15.231(5), c = 15.885(6) Å, β = 100.27(2)°, Z = 4 and V = 2750.76 Å 3. A total of 1456 unique data with F > 2.33σ( F) were refined to values of R and R w of 3.23 and 3.63%, respectively. The structure of 3 consists of the doubly-bridged [Cu 2(O 2CMe) 2(H 2O) 2(bpy) 2] 2+ cation, two considerably disordered ClO 4 − anions and the disordered H 2O solvate molecule. The two acetates are in the familiar η 1:η 1:μ 2 bridging mode; a terminal bpy molecule and one aqua ligand complete five-coordination at each metal atom. The molecule of 4 is very similar to the cation of 3; the aqua ligands of 3 are replaced by two terminal, axial monodentate perchlorato groups. In both 3 and 4, the dimers are stabilized by bpy-bpy stacking interactions, and the precise structural effects of these interactions are described.

The Crystal and Molecular Structure and Properties of Diaqua[N-salicylidene – (S) – (+) – glutamato]copper(II) Monohydrate

The crystal and molecular structure of the title complex was determinated by single crystal X-ray diffraction (R = 0.066 for 1059 observed reflections). The approximately square-pyramidal coordination of Cu(II) results from donor atoms O(12), O(1), N(1), O(5) of one H2O molecule as well as the tridentate Schiff base dianion ligand and from the weakly bonded O(1) donor atom of one other H2O molecule in the apical site. The magnetic behaviour of the complex studied obeys the Curie—Weiss law in the temperature range 94—309 K with a small value of the Weiss constant, θ = 1.4 Κ. A similar cryomagnetic behaviour is also characteristic for the anhydrous compound, [N-salicylidene—(S)—(+)-glutamato]copper(II), obtained by thermal dehydration of the title complex.

A RAMAN Spectroscopic Investigation of Alloxan and Alloxan Monohydrate

Abstract The present Raman investigation of anhydrous alloxan and the misnamed alloxan monohydrate suggests that some of the assignments previously made on basis of the IR spectrum of the anhydrous compound must be changed, i.e., the ones related to the NH stretching and ring breathing modes. The hydrogen bonding network in the crystal of the so called alloxan monohydrate, although extensive, is not strong enough to cause substantial frequency shifts in the NH and CO stretching modes.