On the relationship between the structures of CuII complexes and their chemical transformations

The thermal decomposition of the complexes M ₂ ^I Cu(SO₄)₂ · 6 H₂O and M₂Ni(SO₄)₂ · · 6 H₂O (M^I=NH₄, K, Rb, Tl) containing the complex cation M^II(H₂O)₆ ²+ (M^Il = =Cu, Ni) was studied. The values of the experimental activation energyE obtained for the dehydration reactions of both complex cations were found to be influenced in different ways by the outer-sphere cations present. It was therefore concluded that the activation energy of the decomposition of Cu(H₂O)₆ ²⁺ depends on the degree of tetragonal distortion of this cation, which increases with the ionic radius of cation M^I. TheΔH values of the studied reactions depend less on the structures of the coordination polyhedra.     

Darstellung und Eigenschaften von Na2CuII (SO4)2 · 6 H2O

Preparation and Properties of Na₂Cu^II (SO₄)₂ · 6 H₂O The preparation of the complex compound of Na₂Cu(SO₄)₂ · 6 H₂O is described. Its structure and properties were investigated using spectral methods (u.v.-vis., i.r., n.m.r.), by means of X-ray powder diffraction, and by thermal methods. On the basis of experimental results it is suggested that another member of the Tutton salts series has been prepared, appearring isostructural with them and showing the less distorted coordination polyhedron of [Cu(H₂O)₆]²⁺ from them. On its dehydration oxygen atoms from the sulphate groups enter the coordination sphere of Cu^II and the symmetry of SO₄^2? becomes lower. The experimental results indicate that Na₂Cu(SO₄)₂ · 6 H₂O as also Na₂Cu(SO₄)₂ as likewise Na₂Cu(SO₄)₂ · 2 H₂O are monoclinic.     

The relationship between the structures of Cu(II) complexes and their chemical transformations

The paper reports an attempt to correlate the structures of hydrates of copper(II) sulphate with some characteristic features of the kinetics of their thermal decompositions. Non-isothermal thermogravimetric measurements were employed to obtain values of experimental activation energy and entropy for the dehydration of CuSO₄ · 5 H₂O, CuSO₄ · 3 H₂O and CuSO₄ · H₂O. The values ofE ^* andΔS ^* for the dehydration of CuSO₄ · 3 H₂O were found to be only little affected by the mode of preparation of this compound. On the other hand, the values ofE ^* andΔS ^* for the dehydration of CuSO₄ · ·H₂O are strongly dependent on whether this compound was prepared by thermal decomposition of CuSO₄ · 5 H₂O or CuSO₄ · 3 H₂O, or by crystallization from solution. As regards the crystalline hydrates of copper(II) sulphate, the greatest energetic hindrance for dehydration was observed for CuSO₄ · 3 H₂O. The experimental results are also discussed with respect to the present opinions concerning the possibilities of using thermal analyses to obtain information on the relationship between the structures and reactivities of solids.     

X-ray crystal and molecular structure of sulphato aquotris(benzotriazole) copper(II)benzotriazole

The complex “Cu(SO₄)(btaH)₄·2H₂O” (btaH = benzotriazole) deposited as deep blue crystals from aqueous CuSO₄·5H₂OH₂SO₄btaH solutions been shown by X-ray diffraction methods to be a monohydrate [Cu(SO₄)(H₂O)(btaH)₃·btaH]. The crystals contain five-coordinate, tetragonal pyramidal Cu(SO₄)(H₂O)(btaH)₃ units and bridging btaH molecules linked together by a three-dimensional array of H-bonding interactions.     

TG/DTA/MS Study of the thermal decomposition of FeSO4·6H2O

The thermal decomposition of FeSO₄·6H₂O was studied by mass spectroscopy coupled with DTA/TG thermal analysis under inert atmosphere. On the ground of TG measurements, the mechanism of decomposition of FeSO₄·6H₂O is: i) three dehydration steps FeSO₄·6H₂O FeSO₄·4H₂O+2H₂O FeSO₄·4H₂O FeSO₄·H₂O+3H₂O FeSO₄·H₂O FeSO4+H₂O ii) two decomposition steps 6FeSO₄ Fe₂(SO₄)₃+2Fe₂O₃+2SO₂ Fe₂(SO₄)3 Fe₂O₃+3SO₂+3/2O₂ The intermediate compound was identified as Fe₂(SO₄)₃ and the final product as the hematite Fe₂O₃.     

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.     

Thermal behaviour of new Cu(II) complexes with Schiff bases functionalised with 1,3,5-triazine moieties as potential antibacterial agents

New complexes of type [Cu(L¹)₂(OH₂)]·4H₂O (1), [Cu(L²)(OH₂)]·0.5H₂O (2) and [Cu₃(L³)₂(OH₂)₃]·0.5H₂O (3) were synthesized by [1 + 1], [1 + 2] and [1 + 3], respectively, template condensation of 2,4,6-triamino-1,3,5-triazine and salicylic aldehyde in the presence of copper(II). The features of complexes have been established from microanalytical, IR and UV–Vis data. The thermal analyses have evidenced the thermal intervals of stability and also the accompanying thermodynamic effects. Processes as water elimination and oxidative degradation of the organic ligands were observed. After water elimination, complexes revealed a similar thermal behaviour. The final product of decomposition was copper(II) oxide as powder X-ray diffraction indicated.     

On the relationship between the structures of Cu(II) complexes and their chemical transformations

The experimental activation energies (E ^*) of dehydration of Cu(NH₃)₄(H₂O)SO₄, Cu(en)₂(H₂O)X₂ (X=Cl^?, Br^?), Cu(en)(H₂O)₂SO₄, Cu(py)₂(H₂O)₂SO₄, CuCl₂ · 2H₂O and M ₂ ^I CuCl₄ · 2H₂O (M ^I =NH₄, K, Rb) were obtained from their non-isothermal thermogravimetric curves using the Coats-Redfern method. TheseE ^* values were compared with known data on the structures of the Cu(II) coordination polyhedra in the above complexes. No dependence of theE ^* values was found on either the central atom — released ligand bond length, or the number and lengths of the hydrogen bonds formed by the released water molecules. However, it was found that it is justified to seek some relationship between theE ^* values and the anisotropic temperature factors of the donor atoms of the ligands split off.     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. VI

Non-isothermal studies of the dehydration of double salt hydrates of the type K₂AB₄·M(II)SO₄·6H₂O where AB₄BeF^2?₄ or SeO^2?₄ and M(II)Mg(II), Co(II), Ni(II), Cu(II) or Zn(II) and their D₂O analogues were carried out. Thermal parameters like activation energy, order of reaction, enthalpy change, etc., for each step of dehydration were evaluated from the analysis of TG, DTA and DTG curves. These parameters were compared with the corresponding double sulphate, i.e., K₂SO₄·M(II)SO₄·6H₂O and their D₂O analogues. The role of divalent cation on the thermal properties of dehydration of the salt hydrates and also the effect on the thermal properties due to deuteration were discussed. The order of reaction was always found unity. The values of ΔH were within ～11-～19 kcal mol^?1     

Anion-induced assembly of two distinct copper(II) coordination polymers with a versatile multidentate N-donor ligand

Reaction of a ligand N-(3,5-di-2-pyrazinyl-4H-1,2,4-triazol-4-yl)-2-pyrazinecarboxamide (Hpztp) with CuSO₄ and Cu(acac)₂ (acac = acetylacetonate), respectively, yields two distinct Cu^II coordination polymers {[Cu₃(pztp)₂(SO₄)₂(H₂O)₂]·3H₂O} _n and {[Cu(pztp)(acac)]·0.5H₂O} _n . Both complexes have been structurally determined and also characterized by physicochemical and spectroscopic methods. The results reveal that by using different anions (SO₄ ^2? versus acac^?), the dimensionality (from 2D to 1D) of the resulting coordination architectures as well as conformations and binding fashions of the pztp ligand are significantly changed. That is to say, the selection of anions will play a key role in inducing the formation of the crystalline materials. The thermal stabilities of both complexes have also been explored and discussed.     

Synthese,Kristallstrukturen und thermisches Verhalten von Er2(SO4)3 · 8 H2O und Er2(SO4)3 · 4 H2O

Syntheses, Crystal Structures, and Thermal Behavior of Er₂(SO₄)₃ · 8 H₂O and Er₂(SO₄)₃ · 4 H₂O Evaporation of aqueous solutions of Er₂(SO₄)₃ yields light pink single crystals of Er₂(SO₄)₃ · 8 H₂O. X-ray single crystal investigations show that the compound crystallizes monoclinically (C2/c, Z = 8, a = 1346.1(3), b = 667.21(1), c = 1816.2(6) pm, β = 101.90(3)°, R_all = 0.0169) with eightfold coordination of Er³⁺, according to Er(SO₄)₄(H₂O)₄. DSC- and temperature dependent X-ray powder investigations show that the decomposition of the hydrate follows a two step mechanism, firstly yielding Er₂(SO₄)₃ · 3 H₂O and finally Er₂(SO₄)₃. Attempts to synthesize Er₂(SO₄)₃ · 3 H₂O led to another hydrate, Er₂(SO₄)₃ · 4 H₂O. There are two crystallographically different Er³⁺ ions in the triclinic structure (P 1, Z = 2, a = 663.5(2), b = 905.5(2), c = 1046.5(2) pm, α = 93.59(3)°, β = 107.18(2)°, γ = 99.12(3)°, R_all = 0.0248). Er(1)³⁺ is coordinated by five SO₄^2– groups and three H₂O molecules, Er(2)³⁺ is surrounded by six SO₄^2– groups and one H₂O molecule. The thermal decomposition of the tetrahydrate yields Er₂(SO₄)₃ in a one step process. In both cases the dehydration produces the anhydrous sulfate in a modification different from the one known so far.     

Derivatographic studies on dehydration of salt hydrates and their deuterium oxide analogues. V

Non-isothermal thermal studies of the dehydration of the double salt hydrates of the type M(I)₂SO₄·M(II)SO₄·6H₂O and their D₂O analogues were carried out where M(I) = TI(I) and M(II) = Mg(II), Co(II), Ni(II), Cu(II) or Zn(II). Thermal parameters like activation energy, order of reaction, enthalpy change, etc. were evaluated from the analysis of TG, DTA and DTG curves. These thermal parameters were compared with those of other series, like NH₄(I), K(I), Rb(I) and Cs(I) studied earlier. On deuteration the nature of dehydration altered in the case of Tl₂Zn(SO₄)₂·6H₂O only. The thermal stability of the salt hyd discussed in relation to the salt hydrates of other series. The role of divalent cation on the thermal properties of dehydration of salt hydrates is also discussed. The order of reaction was always found unity. The values of ΔH were within ≈12–≈16 kcal mol^?1.     

Polyhalite and its analogous triple salts

Polyhalite (K₂SO₄ · MgSO₄ · 2CaSO₄ · 2H₂O) and analogue triple salts, where Mg²⁺ is substituted by Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺, have been synthesized. The salts were characterized by thermal analysis, Raman spectroscopy and X-ray powder diffraction. Diffraction patterns and Raman spectra resemble those of natural polyhalite, except K₂SO₄ · CuSO₄ · 2CaSO₄ · 2H₂O. The latter corresponds to the mineral leightonite, which is structurally different.     

Hydrogen bond strength in some beryllium salts,BeXO4·4H2O and Me2Be(XO4)2·2H2O (X = S,Se; Me = K,Rb): Correlation of structural data and infrared spectra

Infrared spectra of the title compounds are presented and discussed in the regions of the uncoupled O–D stretches of matrix-isolated HDO molecules (isotopically dilute samples). The strengths of the hydrogen bonds are analyzed in terms of the respective O_w?O bond distances, the Be–OH₂ interactions (synergetic effect), the proton acceptor capabilities of the sulfate and selenate oxygen atoms as deduced from Brown's bond valence sums of the oxygen atoms, the anti-cooperative effect (proton acceptor and proton donor competitive effect). The infrared spectroscopic experiments reveal that comparatively strong hydrogen bonds are formed in the compounds under study, analogical to other hydrated beryllium salts owing to the large ionic potential of the small Be²⁺ ions. The wavenumbers of ν_OD show that the water molecules in BeSO₄·4H₂O and in the double salts are strongly energetically distorted, i.e. their local symmetries deviate remarkably from the C_2v molecular symmetry (for example, Δν have values of 74 and 36 cm^?1 for H₂O(1) and H₂O(2) in K₂Be(SO₄)₂·2H₂O, and 119 cm^?1 in BeSO₄·4H₂O). The hydrogen bonds in K₂Be(SeO₄)₂·2H₂O are stronger than those in K₂Be(SO₄)₂·2H₂O due to the stronger proton acceptor capability of the SeO₄^2? ions. The proton donor strengths of the water molecules in K₂Be(SO₄)₂·2H₂O and K₂Be(SeO₄)₂·2H₂O are greater than those of the water molecules in BeSO₄·4H₂O and BeSeO₄·4H₂O (i.e. larger deviations from Mikenda's curve) due to the different compositions of the respective beryllium tetrahedra-Be(XO₄)₂(H₂O)₂ in the double salts and Be(H₂O)₄ in the simple ones (proton donor competitive effect). The intramolecular O–H bond lengths are derived from the ν_OD vs. r_OH correlation curve [H.D. Lutz, C. Jung, J. Mol. Struct. 404 (1997) 63].     

Dynamic and controlled rate thermal analysis of halotrichite

Three halotrichites namely halotrichite Fe²⁺SO₄·Al₂(SO₄)₃·22H₂O, apjohnite Mn²⁺SO₄·Al₂(SO₄)₃·22H₂O and dietrichite ZnSO₄·Al₂(SO₄)₃·22H₂O, were analysed by both dynamic, controlled rate thermogravimetric and differential thermogravimetric analysis. Because of the time limitation in the controlled rate experiment of 900 min, two experiments were undertaken (a) from ambient to 430 °C and (b) from 430 to 980 °C. For halotrichite in the dynamic experiment mass losses due to dehydration were observed at 80, 102, 319 and 343 °C. Three higher temperature mass losses occurred at 621, 750 and 805 °C. In the controlled rate thermal analysis experiment two isothermal dehydration steps are observed at 82 and 97 °C followed by a non-isothermal dehydration step at 328 °C. For apjohnite in the dynamic experiment mass losses due to dehydration were observed at 99, 116, 256, 271 and 304 °C. Two higher temperature mass losses occurred at 781 and 922 °C. In the controlled rate thermal analysis experiment three isothermal dehydration steps are observed at 57, 77 and 183 °C followed by a non-isothermal dehydration step at 294 °C. For dietrichite in the dynamic experiment mass losses due to dehydration were observed at 115, 173, 251, 276 and 342 °C. One higher temperature mass loss occurred at 746 °C. In the controlled rate thermal analysis experiment two isothermal dehydration steps are observed at 78 and 102 °C followed by three non-isothermal dehydration steps at 228, 243 and 323 °C. In the CRTA experiment a long isothermal step at 636 °C attributed to de-sulphation is observed.     

Polarographic reduction of aqueous sulfur dioxide

Direct- and alternating-current polarograms of aqueous SO₂ · OH₂ solutions show four reduction waves, more than previously reported. Waves I and II probably result from the electroreduction of SO₂ · OH₂ and HSO⁻₃, respectively; these two waves completely overlap at pH 1 but are partially resolved at higher pH values due to different pH dependence. Reduction of SO₂ · OH₂ involves two electrons and two H⁺ ions and the initial product is probably sulfoxylic acid, H₂SO₂. This product can disproportionate to S⁰ and SO₂ · OH₂ in very acidic media (pH ≤ 1) and, in the limit, double the reduction current of SO₂ · OH₂. Reduction of HSO⁻₃ appears to occur via two paths: one is a two-electron three-H⁺ ion path and the other is a one-electron one-H⁺ ion path. The former dominates at pH ≤ 3 and probably produces H₂SO₂; the latter dominates at pH > 4 and may produce SO⁻₂. H₂SO₂ in less acidic media can react with HSO⁻₃ to yield dithionite species (such as H₂S₂O₄, HS₂O⁻₄ and S₂O²⁻₄) and HSO₂ and SO⁻₂ by dissociation of the dithionite species. Waves III and IV are believed to result from reduction of HSO₂ and SO⁻₂, respectively, to H₂SO₂ species.     

Polyhalite and its analogous triple salts

Polyhalite (K₂SO₄ · MgSO₄ · 2CaSO₄ · 2H₂O) and analogue triple salts, where Mg²⁺ is substituted by Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺, Cu²⁺ and Zn²⁺, have been synthesized. The salts were characterized by thermal analysis, Raman spectroscopy and X-ray powder diffraction. Diffraction patterns and Raman spectra resemble those of natural polyhalite, except K₂SO₄ · CuSO₄ · 2CaSO₄ · 2H₂O. The latter corresponds to the mineral leightonite, which is structurally different. For polyhalite analogues the cell parameters of the triclinic unit cell have been determined from the powder diffraction patterns. The length of the unit cell vectors varies regularly with the ionic radius of the substituted ion M ²⁺ and is explained by changes in the extension of the coordination octahedron of M ²⁺. Thereby increasing distances of the coordinated water molecules at M ²⁺ parallel with decreasing dehydration temperatures of the corresponding polyhalite. Correspondence: Daniela Freyer, Institut für Anorganische Chemie, TU Bergakademie Freiberg, 09599 Freiberg, Germany.     

The self-cooling effect in the process of dehydration of Li2SO4·H2O,CaSO4·2H2O and CuSO4·5H2O in vacuum

The third-law method has been applied to the results of kinetic studies reported in the literature and obtained in this work to determine the E parameters of the Arrhenius equation and investigate the impact of self-cooling on the dehydration kinetics of Li₂SO₄·H₂O, CaSO₄·2H₂O and CuSO₄·5H₂O. The values obtained (104, 98 and 88 kJ mol^-1, respectively) are about 20% higher compared to the literature data calculated by the Arrhenius-plots method. This discrepancy is connected with the severe effect of self-cooling, which can reach several ten degrees at maximum temperatures of experiments. This revised version was published online in July 2006 with corrections to the Cover Date.     

Growth and Thermal,Electrical, Structural Characterization of Mixed Hydrated Single Crystal

Mixed single crystal was made by mixing saturated aqueous solutions of NiSO₄ · 6H₂O and CuSO₄ · 5H₂O by volume (80:20) and the mixture was kept to form the crystals at room temperature by slow evaporation process. After some days, big pieces of greenish blue, dark colored crystals were grown. To determine the weight of NiSO₄ · 6H₂O and CuSO₄ · 5H₂O in the crystal, Ni-DMG complexiometrical and EDTA gravimetrical analysis was done respectively. From this analysis it was concluded that 5.8 molecules of water of crystallization is present in the mixed single crystal. The crystals were characterized by UV-Visible, FTIR and single crystal X-ray diffraction studies. From single crystal XRD lattice parameters have been calculated. All these structural analysis confirms formation of new single crystal. Further, DTA-TGA, dc electrical conductivity and dielectric constant studies were done from the room temperature to 400 °C.From DTA studies it was observed that 5.8 molecules of water of crystallization get dehydrated in four major steps at temperature 115 °C, 150 °C, 240 °C and 325 °C respectively corresponding to the detachment of 1 mole, 3 moles, 1 mole and 0.8 mole of water of crystallization. DC electrical conductivity and dielectric constant studies also show close agreement to the dehydration steps. The observed peaks in the conductivity verses temperature graph have been explained on the basis of release of water molecules and subsequent dissociation of these released water molecules into H⁺ and OH⁻ ions.     

DSC study of melting and solidification of salt hydrates

Most salt hydrates, especially those proposed for thermal-energy-storage applications, melt incongruently. In static systems, this property often leads to differences between the enthalpy of fusion and enthalpy of solidification. By means of differential scanning calorimetry (DSC), these differences have been determined for several salt hydrates. For Na₂SO₄ · 10 H₂O, the enthalpy of solidification at or near the peritectic temperature is never more than 60% of the enthalpy of fusion; further cooling leads to a second phase transition at a temperature corresponding to eutectic melting of mixtures of ice and this hydrate. This asymmetrical melting and freezing behavior of Na₂SO₄ · 10 H₂O decreases its potential as an energy-storing medium and also limits its usefulness for temperature calibration of DSC instruments. Sodium pyrophosphate decahydrate, Na₄P₂O₇ · 10 H₂O, although in some ways a higher temperature analog of Na₂SO₄ · 10 H₂O, exhibited a smaller discrepancy between the enthalpies of fusion and of solidification; its relatively high transition temperature permits a more rapid solidification reaction than is the case for Na₂SO₄ · 10 H₂O. For Mg(NO₃)₂ · 6 H₂O, a congruently melting compound, the magnitude of ΔH of crystallization equalled ΔH of fusion, even when supercooling occurred; a solid-state transition at 73°C, with ΔH = 2.9 cal g^?1, was detected for this hydrate. MgCl₂ · 6 H₂O, which melts almost congruently, exhibited no disparity between ΔH of crystallization and ΔH of fusion. CuSO₄ · 5 H₂O and Na₂B₄O₇ · 10 H₂O exhibited marked disparities. Na₂B₄O₇ · 10 H₂O formed metastable Na₂B₄O₇sd 5 H₂O at the phase transition; this was derived from the transition temperature and verified by relating the observed ΔH of transition to heats of hydration. Peritectic solidification of hydrates can be viewed as a dual process: crystallization from the liquid solution and reaction of the lower hydrate (or anhydrate) with the solution; where ΔH of solidification appears to be less in magnitude than the ΔH of fusion, the difference can be attributed to slower reaction rate between solution and the lower hydrate. New or previously unreported values for ΔH of fusion obtained in this study were, in cal g^?1: Mg(NO₃)₂ · 6 H₂O, 36; Na₄P₂O₇ · 10 H₂O, 59; CuSO₄ · 5 H₂O, 32; Na₂B₄O₇ · 10 H₂O, 33.