Deuterium isotope effect on the heats of hydration of barium chloride

Heats of solution of barium chloride, its mono- and dihydrates, and the deuterated hydrates at 25°C have been measured and combined to calculate the deuterium isotope effect on the heats of hydration of barium chloride. Substitution of D₂O for H₂O in the hydrates enhances the heats of dehydration by 1–2%.     

Spectroscopic characterization of superparamagnetic particles of thermolytic products of ferric sulphate hydrates

Superparamagnetic particles of chemically pure samples, in the system Fe(OH)SO₄/Fe(OH)SO₄·(H₂O), are produced by thermal decomposition of ferric sulphate hydrates. The control of particle size distribution is achieved by successive hydration and dehydration processes monitored by X-ray diffraction, electron microscopy, Mössbauer and IR spectroscopy. The particle size modification is related for the particle growth and two mechanisms are suggested thereon.     

Zur Kenntnis der Hydrate des Bariumchlorids. Röntgenographische,thermoanalytische, Raman- und IR-spektroskopische Untersuchungen

Hydrates of Barium Chloride. X-ray, Thermoanalytical, Raman, and I.R. Data In the system BaCl₂? H₂O the hydrates BaCl₂ · 2 H₂O, BaCl₂ · 1 H₂O, BaCl₂ · 1/2 H₂O, and BaCl₂ · uH₂O were obtained. X-ray powder data, i.r. and Raman spectra, as well as thermoanalytical measurements (TG, DTA) are reported. BaCl₂ · 1 H₂O and BaCl₂ · 1/2 H₂O, which are both isotype with the corresponding hydrates of SrCl₂, were prepared by dehydration of BaCl₂ · 2 H₂O or by back hydration of anhydrous BaCl₂ with the calculated amounts of water. BaCl₂ · uH₂O (u ≈? 1) is formed as the primary product by the reaction of anhydrous BaCl₂ with water vapour at room temperature. Preparation methods of salt hydrates by controlled back hydration of the anhydrous salts are reported.     

Supramolecular Open‐Framework of a Bipyridinium‐Carboxylate Based Copper Complex with High and Reversible Water Uptake

The rigid zwitterionic ligand 1,1′‐bis(4‐carboxylatphenyl)‐(4,4′‐bipyridinium) (pc1) and copper(II) ions give rise to a linear complex [Cu(pc1)₂(H₂O)₄]²⁺, which self assembles in a pseudo tetragonal supramolecular arrangement leading to the supramolecular open‐framework [Cu(pc1)₂(H₂O)₄](Cl)₂ · 8H₂O exhibiting an open structure including water molecules and chlorides in pores. The dehydration of this material occurs at relatively low temperature (70 °C) and results in structure modification accompanied by shrinking of the crystals. Characterization of the obtained material by FT‐IR spectroscopy reveals appearance of coordinated carboxylates groups, which may indicate the formation of coordination polymer after dehydration. Water adsorption (maximum uptake 0.23 g H₂O per g) on dehydrated material allows to restore the initial structure. A large hysteresis in water adsorption‐desorption isotherm is characteristic of a significant modification of the structure during the hydration‐dehydration cycle which is in line with the structural transition determined from thermodiffractometry and FT‐IR spectroscopy.     

A B3LYP study on counterpoise-corrected geometry optimizations for hydrated complexes of [K(H2O)n] and [Na(H2O)n]

We report the basis set dependencies and the basis set superposition errors for the hydrated complexes of K⁺ and Na⁺ ions in relation to the recent studies of the KcsA potassium channel. The basis set superposition errors are estimated by the geometry optimizations at the counterpoise-corrected B3LYP level. The counterpoise optimizations alter the hydration distances by about 0.02–0.03 Å. The enthalpies and free energies for K⁺ + n(H₂O) → [K(H₂O)_n]⁺ and Na⁺ + n(H₂O) → [Na(H₂O)_n]⁺ (n = 1–6) are compared between the theoretical and experimental values. The results show that the addition of diffuse functions to K, Na, and O species are effective. However, it is also found that the counterpoise corrections using diffuse functions work so as to underestimate the free energies for the complexes with increasing the hydration number. The stabilization energies in aqueous solution are larger for a Na⁺ ion than for a K⁺ ion, suggesting the contributions of their dehydration processes to the ion selectivity of the KcsA potassium channel. The changes in coordination distance between the isolated [K(H₂O)₈]⁺ and the [K(H₂O)₈]⁺ in the KcsA potassium channel indicate the importance of hydrogen bondings between the first hydration shell and the outer hydration shells.     

A study of the reaction Na2SO4·10H2O→Na2SO4+10H2O in the temperature range 0 to 25°C

Thermogravimetry was used to obtain data on the isothermal rate of dehydration and hydration of the reaction Na₂SO₄·10H₂O→Na₂SO₄+10H₂O in the temperature range 10 to 25°C. The thermodynamic functions, ΔH, ΔG and ΔS were calculated and compared with data in the literature. The dissociation pressures of Na₂SO₄·10H₂O at temperatures in the range 0 to 25°C were measured in a volumetric dissociation apparatus. The results obtained were compared with those using thermogravimetry and the accuracy of the two techniques was assessed.     

Evaluation of phases in a hydrothermally treated CaO-SiO2-H2O system

The evolution of hydration products with reaction time in a hydrothermally cured CaO-SiO₂-H₂O system, when using quartz of different fineness, was investigated by means of thermal, X-ray diffraction and wet chemical techniques. A combination of second derivative differential thermal-, first derivative thermogravimetric- and the equivalent differential thermal- and thermogravimetric curves provided more critical information about the nature of phases formed than X-ray diffraction alone. Phenomena including overlapping dehydration reactions and interactions of phases during the thermal experiment are discussed and illustrated by examples. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dehydration characteristics of struvite-K pertaining to magnesium potassium phosphate cement system in non-isothermal condition

Struvite-K (KMgPO₄·6H₂O) is the main hydration product of magnesium potassium phosphate cement. Its thermal stability is critical to the properties of magnesium potassium phosphate cement. Therefore, in this study, the dehydration behavior of struvite-K was investigated at N₂ atmosphere in non-isothermal condition. The process was conducted and controlled in a simultaneous TG/DTA analyzer, at heating rates of 2, 5, 10, 15, and 20 K min^?1. The residual mass was always around 58.5% of the initial one, regardless of the heating rate, which corresponds to the dehydration reaction through one step, KMgPO₄·6H₂O → KMgPO₄. The activation energy (E _a) corresponding to the dehydration of struvite-K was evaluated by non-isothermal kinetic analysis based on the application of isoconversional methods (Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods). The calculated results show that Flynn–Wall–Ozawa has slightly higher values of activation energy (E _a) and correlation coefficients (R ²). Both methods have been proved to be suitable for analyzing dehydration behavior of struvite-K.     

Rare earth phosphate powders RePO4·nH2O (Re=La,Ce or Y) II. Thermal behavior

The thermal behavior, thermostructural and morphological changes, of rare earth phosphate powders RePO₄·nH₂O (Re=La, Ce or Y) was investigated up to 1500°C using high temperature X-ray diffraction, FT-infrared and Raman spectroscopies and thermogravimetry coupled with differential thermal analysis. The hydration water of the compounds was zeolitic (for Re=La or Ce) or coordinated (for Re=Y) and was associated with a divariant or a monovariant equilibrium of dehydration, respectively. The high temperature anhydrous monoclinic phase LaPO₄ or CePO₄ formed irreversibly at about 750°C after the total dehydration of the hexagonal hydrated structure while the dehydration of the monoclinic YPO₄·2H₂O phase began from about 190°C with its simultaneous decomposition into tetragonal YPO₄. A polytrioxophosphate secondary minor phase Re(PO₃)₃ resulting from adsorbed H₃PO₄ was formed at 950°C and decomposed at 1350°C. The particle morphology did not change with the temperature but grain coalescence occurred below 1000°C.     

The kinetic and thermodynamic study of KNiPO4·H2O from DSC and TG data

The DSC and TG data showed the dehydration process occurring over the range of 160?C300?°C. The XRD patterns of the synthesized KNiPO₄·H₂O and the calcined product at 350?°C with exposing in the air over 8?h are indexed as the KNiPO₄·H₂O structure, whereas at 600?°C is indexed as KNiPO₄ structure. Hence, these data confirmed that the water molecule was eliminated from the structure at 300?°C, after that the spontaneously reversible hydration?Crehydration process was observed. The activation energy and pre-exponential factor were calculated by Kissinger, Ozawa, and KAS equations. According to the DSC curves, the enthalpy change (??H) of dehydration process can be calculated and was found to be 100.12?kJ?mol^?1. Besides, we suggested another new method to determine the isokinetic temperature value using spectroscopic data. The surface area of synthesized hydrate and its calcined product at 350?°C with exposing in the air at over 8?h were found to be 21.48 and 134.3?m²?g^?1, respectively. The reversible hydration?Crehydration process was observed, and the surface area of final product at 350?°C (aging time over 8?h) is higher than that of the synthesized compound. This behavior is important to develop alternative desiccant materials or other process based on the rehydration mechanism with increasing the surface area.     

Pseudopolymorphism and phase stability of 7-piperidino-1,2,3,5-tetrahydroimidazo-[2,1-b]quinazolin-2-one (DN-9693)

The phase stabilities of three pseudopolymorphs of DN-9693 were studied by using thermogravimetry and differential thermal analysis. The thermal dehydration of DN-9693·2HCl·H₂O proceeds by the mechanism of two-dimensional growth of nuclei. The thermal dehydration of 0.5 mol of H₂O per mol of DN-9693·2HCl·2H₂O, and that of 2 mol of H₂O per mol of DN-9693·2HCl·3H₂O, proceed by the mechanisms of three-dimensional diffusion and three-dimensional phase boundary reaction, respectively, but the dehydration followed overlaps with the thermal elimination of HCl. The half-lives for the dehydration at 25°C show that DN-9693·2HCl·H₂O is the most stable form.     

Study of the products of the dehydration reaction of CuSO4 · 5H2O in X-shaped and elliptic nuclei

The products of the dehydration of CuSO₄ · 5H₂O under different conditions have been studied by the methods of local X-ray diffraction analysis and EPR. It is shown that the dehydration in vacuo when X-shaped nuclei are formed proceeds through the formation of an intermediate product having a monohydrate composition and a crystalline lattice close to the initial lattice of the pentahydrate. Then the amorphization and crystallization of CuSO₄ · H₂O follows. When dehydration occurs in water vapour through ellipsoidal nuclei the structure of the trihydrate formed is oriented relative to the initial structure of CuSO₄ · 5H₂O.     

水环境对GC和AT碱基对质子转移的影响

采用B3LYP/DZP++的方法研究了第一水化层作用和连续化处理的水溶剂作用对鸟嘌呤-胞嘧啶(GC)碱基对和腺嘌呤-胸腺嘧啶(AT)碱基对质子转移反应的影响. GC和AT碱基对在连续化水溶剂作用下,均发生单质子转移(SPT1)和分步的双质子转移(DPT),而在第一水化层5 个水分子的作用下(GC·5H₂O,AT·5H₂O)或同时考虑第一水化层作用和连续化水溶剂作用(GC·5H₂O+PCM,AT·5H₂O+PCM)时,GC和AT碱基对的质子转移均只得到单质子转移反应(SPT1). 单质子转移过程中的活化能变化情况表明：第一水化层对GC和AT碱基对结构和质子转移影响较大,水环境对碱基对的作用主要发生在第一水化层.     

Eyring parameters of dehydration processes

Thermogravimetry was used in the study of the kinetics of dehydration of MnSO₄·5H₂O, CuSO₄·5H₂O and 3CdSO₄·8H₂O under static air atmosphere. The values of the kinetic and thermodynamic parameters for each stage of thermal dehydration were calculated from α(T) data by using the integral method, applying the Coats-Redfern approximation. The best model for all stages of dehydration is random nucleation model F1. The dependencies of enthalpy on entropy of activated complexes for different kinetic models were described. The linear relation was calculated between the Gibbs energy of activated complexes and the maximum dehydration rate temperature for analysed dehydration processes.     

A hybrid carboxylate-water decamer with a discrete octameric water moiety self-assembled in a 2D copper(II) coordination polymer

An octameric water moiety which consists of a chairlike water hexamer and two pendent water molecules in the 1,4-diaxial positions and shows a similar structure to the hydrocarbon(1r,4r)-1,4-dimethylcyclohexane,is unambiguously trapped in a2D Cu(Ⅱ) mixed-ligand coordination polymer,{[Cu2(bpp)2(H2O)2(bpda)2 ].6H2O} n(1)(bpp = 1,3-bis(4-pyridyl)propane and H2 bpda =2,2’-biphenyldicarboxylic acid).The water octamer can be extended into a hybrid carboxylate-water decamer when carboxylic oxygen atoms from bpda2 are involved.Interestingly,the present hybrid decamer bears a similar structural topology to a butterfly(H2O) 10 cluster.The reversible dehydration/hydration of 1 is determined by X-ray powder diffraction studies.     

Synthesis and thermal dehydration of hexaaquarhodium(III) phosphates

Complex salts [Rh(H₂O)₆]PO₄ (I) and [Rh(H₂O)₆]PO₄ · H₂O (II) were obtained. Dehydration processes of compounds I and II were studied by thermogravimetry and differential scanning calorimetry. The heat effect for the loss of 0.82 ± 0.01 H₂O (hydration) molecule was found to be 54 ± 1 kJ/mol, while that for the loss of coordinated H₂O is 47 ± 1 kJ/mol (for I) and 43 ± 1 kJ/mol (for II). The solid phases of dehydration products were studied by X-ray powder diffraction, IR and ³¹P MAS NMR spectroscopy, and they were found to be polymers.     

Highly Selective Water Adsorption in a Lanthanum Metal–Organic Framework

We present a new metal–organic framework (MOF) built from lanthanum and pyrazine‐2,5‐dicarboxylate (pyzdc) ions. This MOF, [La(pyzdc)_1.5(H₂O)₂] ? 2 H₂O, is microporous, with 1D channels that easily accommodate water molecules. Its framework is highly robust to dehydration/hydration cycles. Unusually for a MOF, it also features a high hydrothermal stability. This makes it an ideal candidate for air drying as well as for separating water/alcohol mixtures. The ability of the activated MOF to adsorb water selectively was evaluated by means of thermogravimetric analysis, powder and single‐crystal X‐ray diffraction and adsorption studies, indicating a maximum uptake of 1.2 mmol g^?1 MOF. These results are in agreement with the microporous structure, which permits only water molecules to enter the channels (alcohols, including methanol, are simply too large). Transient breakthrough simulations using water/methanol mixtures confirm that such mixtures can be separated cleanly using this new MOF.     

Flexible 3D porous metal-organic framework exhibiting selective adsorption for H2O over organic solvents

A new flexible 3D porous metal-organic framework (MOF) with 1D open nanotube,[Co2(μ5-CTAI)(dpe)(H2O)2]n·6n(H2O)(1) (CTA=cyclohexane-1,2,4,5-tetracarboxylic acid,dpe=1,2-di(4-pyridyl) ethylene) has been prepared and structurally characterized.Meanwhile,each 1D nanotubes filled with 1D water chain with dimension of 13.711 × 12.275 2.Compound 1 represents a new example that collapse/deform upon dehydration/hydration and shows adsorb H 2 O selectively over organic solvents.     

Variable temperature PXRD investigation of the phase changes during the dehydration of potassium Tutton salts

The thermal dehydration of the potassium Tutton salts K₂M(SO₄)₂·6H₂O (M = Mg, Co, Ni, Cu, Zn) was investigated using thermal gravimetric analysis (TG), differential scanning calorimetry (DSC), FTIR, and variable temperature powder X-ray diffraction. While each Tutton salts lost all six waters of hydration when heated to 500 K, the decomposition pathway depended on the divalent metal cation. K₂Ni(SO₄)₂·6H₂O lost all six waters in a single step, and K₂Cu(SO₄)₂·6H₂O consistently lost water in two steps in capped and uncapped cells. In contrast, multiple decomposition pathways were observed for the magnesium, cobalt, and zinc Tutton salts when capped and uncapped TG cells were used. K₂Zn(SO₄)₂·6H₂O lost the waters of hydration in a single step in an uncapped cell and in two steps in a capped cell. Both K₂Mg(SO₄)₂·6H₂O and K₂Co(SO₄)₂·6H₂O decomposed in a series of steps where the stability of the intermediates depended on the cell configuration. A greater number of phases were often observed in DSC and capped-cells TG experiments. A quasi-equilibrium model is presented that could explain this observation. These results highlight that experimental conditions play a critical role in the observed thermal decomposition pathway of Tutton salts.     

Thermal studies on yttrium,neodymium and holmium oxalates

The thermal decomposition patterns of Y₂(C₂O₄)₃ · 9 H₂O, Nd₂(C₂O₄)₃ · 10 H₂O and Ho₂(C₂O₄)₃ · 5.5 H₂O have been studied using TG and DTG. The hydrated neodymium oxalate loses all the water of hydration in one step to give the anhydrous oxalate while Y₂(C₂O₄)₃ · 9 H₂O and Ho₂(C₂O₄)₃ · 5.5 H₂O involve four or more dehydration steps to yield the anhydrous oxalates. Further heating of the anhydrous oxalates results in the loss of CO₂ and CO to give the stable metal oxides.