Christo Balarew

Application of the hard and soft acids and bases concept to explain ligand coordination in double salt structures

Abstract The coordination polyhedra in 43 double salt structures are examined. Each structure is formed by at least two kinds of polyhedra. The differences in the environment around the metal ions are explained using HSAB concept. The values of hardness for 25 cations are calculated according to Klopman. A factor χ = H acid · H base , where H is the hardness value, is introduced. The value of this factor can be used as a criterion for the stability of the complexes. The possibilities which the χ factor gives in explaining ligand coordination in known structures as well as for predicting structures for double salts are illustrated.

IUPAC-NIST Solubility Data Series. 73. Metal and Ammonium Formate Systems

This volume reviews the metal and ammonium formate solubility data published up to 1995. So far as the editors are aware, all the solubility data published during this period have been reviewed. Preference has been given to data published in numerical form. Data that appeared only in graphical form may not appear in this volume. In each section the metal atoms are arranged in the order (group) in which they appear in the Periodic Table. Metal formates are crystalline solids having some interesting chemical and physical properties. Several of these salts are important because they have nonlinear optical properties. Specific examples are: LiCHO2⋅H2O (3), NaCHO2 (4), Sr(CHO2)2, and Sr(CHO2)2⋅2H2O, Ba(CHO2)2, formates of Sc, Y and the rare earth elements having the general formula Me(CHO2)3⋅nH2O (where Me=Sc, Y, La, Ce, Pr, Nd, Sm…Lu) and some double salts and mixed salts such as NaCd(CHO2)3, BaCd(CHO2)4⋅2H2O and Li0.9Na0.1CHO2. Some metal formates have useful electric or magnetic characteristics. Thus, Cu(CH...

Pyro- and ferroelectric properties of nGly.MeCl2.2H20 (Me = Mn, Co; n = 1, 2)

Abstract The Gly. MeC12.H20 systems (Me=Mn, Co) have been investigated at 25°C and the crystallization fields of all four nGly. MeCl2.2H20 (Me=Mn, Co; n=1,2) compounds are established. The pyro-and ferroelectric properties and the electrical conductance on single crystals of these compounds are studied. It is found that: (i) the manganese compounds show higher pyro-and ferroelectric effects fian those of the cobalt compounds; (ii) the compounds Gly. MeCl2.2H20 show higher ferroelectric effects than do 2Gly. MeCl2.2H20, and (iii) the pyroelectric effects of Gly. MeCl2.2H20 and 2Gly. MeCl2.2H2O are commensurable. The differences in ferroelectric properties of the Gly. MeCl2.2H2O and 2Gly. MeCl2.2H2O compound types are ascribed to the different kinds of bonding of the Cl-ions in their crystal structures. Highest pyro-and ferroelectric effects are found with Gly. MnCl2.2H20.

Divalent metal halide double salts in equilibrium with their aqueous solutions: I. Factors determining their composition

Abstract Using a few simple assumptions based on the hard and soft acid and base model and the bond-valence model, we explain why the five most common double salt compositions xMeX 2 · yMe ′ X 2 · z H 2 O ( Me , Me ′ = Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Cd; X = Cl, Br) found in equilibrium with the corresponding saturated solutions at room temperature will have x : y : z equal to 2:1:12, 1:1:8, 1:1:6, 1:2:6, and 1:4:10 and predict that these will belong to nine structural types. About 90% of the double salts observed under these conditions have one of these compositions and the remainder have closely related structures. We also make predictions about the chemical species expected in saturated solutions.

Role of the crystal field stabilization energy in the formation of metal(II) formate mixed crystals

A relationship between the distribution coefficient values and the factors determining the isomorphous substitution of some metal(II) formates (Mg, Mn, Fe, Co, Ni, Cu, Zn, Cd) has been found, given by D 2 / 1 = [ M 1.0 M 2.0 ] 2 exp ⁡ a ⋅ f [ Δ R R ] + b ⋅ ϕ ( Δ e ) + c ⋅ ψ ( Δ s ) R T , where Δ R/R is the relative difference in the ionic radii of the intersubstituting ions, Δɛ is the difference in the Me O bond energy, Δ s is the difference in the crystal field stabilization energy. The pre-exponential term represents the balance in bonding factors between the ions in the crystal and in the aqueous solution, in the case of ideally mixing in the solid state. The exponential term takes into account the enthalpy of mixing in the solid state. For the isostructural formate salts in which the substitution of a given cation by another one occurs in equivalent octahedral positions, the difference in the crystal field stabilization energy exerts the most important influence on the enthalpy of mixing.

Similarities and peculiarities between the crystal structures of the hydrates of sodium sulfate and selenate.

The crystal structures of the two hydrates Na2SeO4·10H2O and Na2SeO4·7.5H2O are studied for the first time. The structures of Na2SO4·10H2O and Na2SO4·7H2O are reinvestigated as a function of temperature with respect to the degree of disorder of the O atoms of SO4(2-) in the decahydrate and the O atom of water in the heptahydrate. For Na2SO4·10H2O, the unit site occupancy factor (SOF) of O atoms of SO4(2-) was determined at 120 K. After the temperature dependence of the lattice parameters was studied from 120 to 260 K, it was shown that SOF decreased from 1.0 at 120 K to 0.247 at room temperature. The interesting fact that two salts with different chemical compositions and different crystal structures (Na2SO4·7H2O, tetragonal, space group P4(1)2(1)2 and Na2SeO4·7.5H2O, monoclinic, space group C2/c) can act mutually as a crystal nucleus is accounted for by similarities in certain fragments of their crystal structures. This phenomenon is attributed to similarities between particular elements of their structures.

Influence of complexation on the composition of equilibrium phases in the system of Ce2(SO4)3-La2(SO4)3

The cocrystallization of Ce2(SO4)3 and La2(SO4)3 is studied in aqueous and H2SO4 (150 g/dm3) solutions at 25 °C and 64 °C. The effect of the formation of inner sphere sulfate complexes of the type LnSO4+ in determining the composition of the equilibrium phases is revealed.

Crystallization Sequence of Brines–Geometrical Principles for a Computer Assisted Calculation

Summary. A computer assisted calculation of the crystallization sequence of a brine is performed on the basis of the respective phase diagrams at 25°C. The nature of the solids and the mass balance are determined. The calculation gives immediate quantitative information of the brine behavior during evaporation. The calculation is performed assuming that i) the solids are always in equilibrium with the liquid, i.e. that some solid phases can be partially or completely redissolved during evaporation, or ii) the solids are separated from liquid by sedimentation and no redissolution is possible. The seasonal or day-night fluctuations of temperature and metastable equilibria have not been taken into account.Zusammenfassung. Die Kristallisationsabfolge beim Abdampfen von Salzsolen wurde bei 25°C aufder Basis der entsprechenden Phasendiagramme computerunterstützt berechnet. Dabei wurden sowohl die auskristallisierenden festen Phasen bestimmt als auch deren Massenbilanzen ermittelt. Um quantitative Information über das Abdampfverhalten von Salzsolen zu erhalten, wurden diesen Berechnungen zwei Grenzannahmen zugrunde gelegt: i) das Fest-flüssig-Gleichgewicht stellt sich laufend ein, sodaß sich feste Phasen während des Verdampfungsprozesses teilweise oder vollständig wieder auflösen können, bzw. ii) die festen Phasen sedimentieren und trennen sich von der flüssigen Phase, sodaß keine Wiederauflösung möglich ist. Tages- bzw. jahreszeitliche Temperaturschwankungen sowie metastabile Gleichgewichte wurden nicht berücksichtigt.

On the crystallization kinetics of highly soluble salts

Abstract For the spontaneous crystallization of highly soluble salts, a sufficiently high concentration of certain ionic species (complexes) or clusters has to be created in the solution, so that their grouping could yield a suitable crystal nucleus in a reasonably short time. The lowest critical supersaturation needed for nucleation and the highest rate of crystallization are displayed by those salts whose complexes in the solution have analogues in the crystal structure of the crystallizing salt, i.e., when the structure and the composition of the complexes enable their incorporation into the crystal lattice of the crystallizing salt with minimum changes. From this point of view a crystallochemical nucleation mechanism for explaining the Ostwald step rule is advanced. Concerning the rate of crystallization this concept was confirmed by studies on the system Na+, Mg2+/Cl–, SO42–//H2O and by parallel Raman spectroscopic studies of the microstructure of these solutions. It was established that upon increasing the concentration of Mg2+ ions and respective lowering of the water activity in the solution, the variety of the SO42– complexes increases. A direct correlation was found between the presence of various SO42– associations and the rate of crystallization of the corresponding salts in these systems.

Untersuchung des Systems NaAl(SO4)2−CsAl(SO4)2−H2O bei 25°C und der daraus entstehenden festen Phasen

The solubility diagram of the system NaAl(SO4)2−CsAl(SO4)2−H2O was investigated at 25°C. This is a system in which β-and γ-alums participate. The fields of cristallization are outlined. There is one wide field of cesium aluminium alum and one, very narrow, of sodium aluminium alum. The eutonic point of the system lies at the composition of the liquid phase corresponding to 27.90 wt.% NaAl(SO4)2 and 0.008 wt.% CsAl(SO4)2. It was found that mixed crystals are not formed in the system. The solid phases were investigated by X-ray diffraction andDTA.