The Precipitation of Alkaline-Earth Metal Oxalate Powders from Aqueous Solution. Crystal Numbers and Final Sizes

The precipitation magnesium oxalate dihydrate, calcium oxalate monohydrate, strontium oxalate monohydrate and barium oxalate hemihydrate was studied from equivalent solutions of concentrations from 0.001 M to 0.5 M, at pHs from 7 to 6, by optical microscopy and other methods. Crystal growth started after induction periods: the precipitations were heterogeneously nucleated at low supersaturations and homogeneously nucleated at medium to high supersaturations. The crystal form and numbers of the final precipitates depended on the type and number of the nuclei (and crystallites) formed during the induction periods. Crystal numbers at medium to high supersaturation, increased with increasing initial mean metal oxalate concentrations according to the relation, N = N₁c; β was 5 for calcium oxalate precipitations and β was 6 for the other metal oxalate precipitations. The N₁ values increased in the order MgC₂O₄ · 2 H₂O < BaC₂O₄ · 1/2 H₂O < SrC₂O₄ · H₂O < CaC₂O₄ · H₂O. The final crystal lengths, in this supersaturation range, then decreased (from maximum values) with increasing initial concentrations according to the relation, l_fin = l₁/C_MOx^β, where γ was 1.3 to 1.6. For precipitations from solution of any concentration at any pH, smaller crystals were obtained in the precipitates of the metal oxalate of lower solubility.     

The Precipitation of Alkaline-Earth Metal Carbonate Powders from Aqueous Solution. Crystal Numbers and Final Sizes

The precipitations of magnesium carbonate trihydrate, basic magnesium carbonate and calcium, strontium and barium carbonates was studied from equivalent solutions of concentrations from 0.0005 M to 1M, at pHs from 10 to 7, by optical microscopy and other methods. Crystal growth started after induction periods: the precipitations of the more sparingly-soluble metal carbonates — mainly studied at medium to high supersaturation — were homogeneously nucleated while the magnesium carbonate trihydrate precipitations — studied at low supersaturations at pH ≦ 7.6 — were heterogeneously nucleated. The crystal forms and numbers of the final precipitates depended on the type and numbers of nuclei (and crystallites) formed during the induction periods. Crystal numbers generally increased with increasing initial mean metal carbonate concentration according to the relation N = N₁C_MCO3^β; β was 3 for the metal carbonate precipitations and β was 4 for the basic magnesium carbonate precipitations. N₁ values increased in the order basic MgCO₃ (at pH ≧ 9), or MgCO₃ · 3H₂O (at pH ≦ 7.6) < CaCO₃ < SrCO₃ < BaCO₃. The final crystal lengths then generally decreased, from maximum values, with increasing initial concentration according to the relation l_fin = l₁/C^γ, where γ was 0.7 and 1.0. For precipitation at any concentration and pH, smaller crystal sizes were generally obtained in precipitates from solutions of the metal carbonate of lower solubility.     

The precipitation of alkaline-earth metal and transition metal ‘oxinate’ powders from aqueous solution. Crystal numbers and final sizes

The precipitation of barium strontium, calcium, magnesium, zinc, cadmium and lead, manganese, cobalt, nickel and copper 8-quinolinolates (‘oxinates’) was studied from equivalent solutions, at pHs from 4.5 to 10, by optical microscopy: the metal cation and overall ‘oxinate’ with ‘oxine’ concentrations were varied from 0.0002 to 0.020 M (while the mean metal oxinate concentrations varied from 10⁻⁷ to 0.001 M). Crystal growth started after induction periods; the precipitations were heterogeneously nucleated at low supersaturations and homogeneously nucleated at medium to high supersaturations. The final precipitate crystal numbers depended on the number of nuclei formed during the induction periods. Crystal numbers at medium to high supersaturations increased with increasing initial metal oxinate concentration according to the relation, The final crystal lengths in this supersaturation range then decreased (from maximum values) with increasing initial mean metal oxinate concentration according to the relation, For precipitation from solutions of any concentration at any pH, smaller crystals were generally obtained in the precipitates from solutions of the metal oxinate of lower solubility.     

The precipitation of alkaline-earth metal and transition metal oxalates from aqueous solution. Induction periods and nucleation rates

The precipitation of magnesium, calcium, strontium and barium oxalates and of manganous, ferrous, cobalt, nickel and copper oxalates was studied from equivalent aqueous solutions at 22°C: the initial overall concentrations (C) generally varied from 0.001 to 0.2 M and the saturation ratios (S_mox) varied from <10 to >3000. The induction periods before the main growth surge were measured and nucleation rates were determined from final crystal numbers and induction periods. Precipitation occurred through homogenous nucleation: the critical nuclei in supersaturated alkaline-earth metal oxalate solutions were formed by aggregation of 6–8 M⁺⁺Ox⁻ ion-pairs while the critical nuclei in supersaturated transition metal oxalate solutions were formed by aggregation of 6–8 MOx complexes (to units of 3–4 M⁺⁺MOx₂⁻ ion-pairs). Over the range studied, the nucleation rates then varied with saturation ratios according to the relation, Nucleation rates at any saturation ratio decreased in the order Mg > Sr, Ba > Ca and Fe > Mn > Co, Cu > Ni; that is, generally in the order of increasing M⁺⁺–Ox⁻ and M⁺⁺–MOx₂⁻ bond strengths and increasing surface energies of the metal oxalate crystals. Induction periods decreased with increasing-concentration and saturation ratio; over The factors t _C1 and t _S1 depended in turn on the ‘rate constants’ for nucleation and growth during the induction periods and on metal oxalate solubilities.     

The precipitation of barium sulphate and chromate powders from aqueous solution with slow development of supersaturation. Crystal numbers and final crystal sizes

The precipitations of barium sulphate and chromate were studied by slow addition of anion to metal cation solution at 20°C, to give final equivalent metal salt solutions; the final solute concentrations (C_fin) were varied from 0.002 to 0.30 mol l⁻¹ while the rates (R) of addition of anion were varied from 10⁻⁴ to 10⁻² ion l⁻¹. At first, mainly heterogeneous nuclei formed continuously during induction periods; then, as the metal salt concentration in solution increased, homogeneous nucleation soon predominated. This second nucleation process probably attained its maximum rate when the metal salt concentration in solution reached its maximum value (C_max) and then probably terminated quite rapidly. Some further nuclei also formed during the growth process when crystal growth was prolonged. The final nucleus numbers (N), and thence the crystal numbers for slow precipitations from very dilute solutions were then rather higher than the number N ∞ (het) of heterogeneous nuclei in solution: nucleus numbers then increased with increasing mixing rate according to the relation, (where β = 0.7–0.9) (where β = 0.7–0.9). The final average crystal lengths of any precipitate were then 2 to 40 times the sizes noted for rapid precipitation from equivalent solutions of the same concentration: generally, final lengths varied with mixing rate according to the relation, .     

The precipitation of lead sulphate from aqueous and aqueous alcohol solutions: Nucleation,final sizes and morphology

The precipitation of lead sulphate was studied from 0.0001 to 0.01 M aqueous solutions (supersaturations 3 to 600) and from 20% aqueous ethanediol, methanol and ethanol solutions, in polypropylene beakers, at ambient temperature: the experimental techniques were conductivity measurements and optical microscopy. The precipitations were heterogeneously nucleated at low supersaturations and homogeneously nucleated at intermediate to high supersaturations. New crystal morphologies generally developed at some what higher supersaturations in the aqueous alcohol systems. The final crystal lengths at first increased with increasing initial metal salt concentration and then decreased with this parameter; the largest crystals at any concentration were obtained from solutions in which lead sulphate solubility was highest. The critical supersaturations (for the onset of homogeneous nucleation) increased from 36 (in water) to 50 (in 20% aqueous ethanol): the surface energies for the formation of nuclei correspondingly increased from 90 to 110 mJ m⁻² in good agreement with the Nielsen-Söhnel relation. The nucleation and crystal growth processes are taking in an aqueous environment of similar water activity to that of the bulk solutions.     

The precipitation of calcium carbonate powders from aqueous solution with slow development of supersaturation. Induction periods,crystal numbers and final sizes

The precipitation of calcium carbonate was studied by slow addition of anion solution to excess cation solution and by slow mixing of equivalent cation land anion solutions at 20 °C: the final solute concentrations (C_fin were varied from 0.01 to 0.75 mole 1⁻¹ while the rates (R) of addition of ions were varied from 0.06 to 6 · 10⁻³ ion 1⁻¹ sec⁻¹. At first, mainly heterogeneous nuclei formed continuously during induction periods; then, as the metal salt concentration in solution increased, some more heterogeneous nuclei formed but homogeneous nucleation soon predominated. The second nucleation process probably attained its maximum rate when the metal salt concentratio in solution reached its maximum value (C_max) and then probably terminated quite rapidly. Some further nuclei also formed during the growth process when crystal growth was prolonged. The final nucleus numbers (N) (and thence the crystal numbers) for slow precipitations from dilute solutions were then rather higher than the optimum number N∞ (het) of heterogeneous nuclei in the solution; nucleus numbers then increased with increasing maxing rate according to the relations . These numbers were similar to those noted for rapid precipitation – onto homogeneous nuclei – from calcium carbonate solutions of concentrations somewhat lower than the C_max values. The final average crystal lengths of any precipitate then generally varied with mixing rate according to the relations, . where l₁ values increased with (C_fln)^0.33.     

The precipitation of alkaline-earth metal molybdate powders from aqueous solution. Crystal numbers,final morphology and sizes

The precipitation of barium, strontium and calcium molybdates was studied from neutral equivalent solutions of concentrations from 0.0004 to 0.4 M at 25 °C. Crystal growth started after induction periods; the precipitiations were heterogeneously nucleated at low supersaturations and homogeneously nucleated at medium to high supersaturations. Barium molybdate was precipitated as tetragonal bipyramids, strontium molybdate generally as prisms and calcium molybdate as platelets. Crystal numbers at medium to high supersaturations increased with increasing inital metal molybdate concentrations according to the relation, The final crystal lengths in this range than decreased from maximum values (at the critical concentrations) with increasing initial metal molybdate concentrations according to the relation. Generally, for precipitation from solutions at any concentration, larger crystals were obtained in the precipitates of the salt of higher solubility.     

The Precipitation of Sparingly-Soluble Alkaline-Earth Metal and Lead Salts with Slow Development of Supersaturation (Slow Anion and Hydroxyl Ion Addition): Kinetics of Nucleation and Induction Periods

Barium and lead sulphate and chromate precipitations were studied at 20° to 95°C at precipitation rates varying from 10⁻³ to 10⁻⁷ ion l⁻¹ sec⁻¹: the supersaturation was developed by slow direct addition of anion to metal nitrate solution and by neutralisation of equivalent metal salt in excess acid solution. Slow heterogeneous nucleation occurred onto particles dispersed within the aqueous solution. The nucleation rate at any time was Where k_n is the rate constant for heterogeneous nucleation, N_∞ is the maximum number of potential nuclei, n_t is the number of nuclei after time t, I. P_t is the ionic product (C_mt)(C_mt) and 2π is the number of metal salt ions in the critical nucleus, generally eight. Crystal growth started after induction periods (t̄) at times just after the times for maximum rate of formation of nuclei. The induction periods (t̄) for precipitations from solutions of initial cation concentration ^cM₀ varied with precipitation rate (R) according to the relation, where γ = π/(π + 1) and k₁ (the unit reciprocal induction period) = . Nucleation rate constants for different precipitations were estimated from the k₁ values and are tabulated. For slow precipitations by direct anion addition, the rate constants were lower for precipitation from solution of the salt of greater solubility. The rate constants for slow precipitation of metal chromates from acid solution were far lower than those for slow precipitation by direct chromate addition. Rate constants decreased somewhat with rise in precipitation temperature.     

Supersaturation and crystal size distribution changes during the precipitation of Nickel ammonium sulphate hexahydrate

The desupersaturation of nickel ammonium sulphate aqueous solutions, during the precipitation of the hydrated salt, has been followed by refractive index measurements. The addition of seed crystals has a considerable effect on the desupersaturation process: the induction and latent periods and the crystal size distribution are all greatly reduced. The precipitated crystal size follows V . WEIMARN'S rules, viz, the median size (a) passes through a maximum with increasing supersaturation for a given crystallization time, and (b) decreases with increasing supersaturation, for precipitations which have virtually ceased. The crystal yield increases with both supersaturation and time, but the size distribution remains fairly constant with time for supersaturations, S > 2.     

Homogeneous nucleation in cooling crystallization

Nielsen's equation has been applied for cooling crystallization of KCl from watery solutions. In the calculations activities are used instead of concentrations, the temperature and concentration dependence of both the activity and diffusion coefficients are considered. It is found that A) the interfacial tension between the crystal and its saturated solution is < 2.5 erg/cm², which is less by two orders of magnitude than that of between crystal and vacuum; B) homogeneous nucleation can take place even at very small supersaturations (ln S < < 0.01), which is unusual in precipitation.     

The precipitation of sparingly-soluble metal salts from aqueous solution: Heterogeneous nucleus numbers at low to intermediate supersaturation

The precipitation of series of alkaline-earth metal and transition hydroxides, sulphates, chromates and molybdates, hydrogen phosphate carbonates, oxalates and ‘oxinates’ were studied in aqueous solution of low to intermediate supersaturation. Heterogeneous nucleation probably occurred onto micro-crystalline particles of some siliceous mineral (of the trigonal, hexagonal or cubic system), dispersed in the solution. The heterogeneous nucleus numbers for these precipitations then depended on the rates of the heterogeneous nucleation onto these substrates and the rates of the mononuclear growth of nuclei to crystallites (during the induction periods). Generally, N_het values in polypropylene and glass beakers, at low supersaturation, varied from 10⁴ to 10¹³ dm⁻³: the N_het values then increased slightly with concentration and supersaturation according to the relation N_het = K_N^β, where K_N is a function of the metal salt surface energy and an ‘epitaxy’ factor; β = 0.4–0.5. In turn, at any supersaturation, log N_het = log N + Fσ, where N and F were constants for any precipitation: N_het values then increased from 10⁴ to 10⁸ times for increase in σ from 50 to 150 mJ m⁻². At any supersaturation and surface energy, N_het values increased in the order monoclinic < orthohombic < tetragonal < trigonal crystals.     

On the kinetic of crystallization of zinc oxalate (II). Determination of the specific surface energy at the crystal solution interface by kinetic studies

An apparatus based on turbidimetry was constructed for studying the kinetics of crystallization of sparingly soluble salts. The kinetics of crystallization of zinc oxalate was investigated at various supersaturations and pHs of the medium. The specific surface energy at the crystal-solution interface was determined from the induction periods of the S-shaped curves by means of the classical theory of nucleation. The calculations were made using the slope of the logarithmic dependence of I or τ, respectively, on supersaturation (equations 1 and 2) and the critical supersaturation which was also determined on the basis of kinetic data. Various values of σ were found for the different supersaturations. Different values for this quantity were also obtained when supersaturation was presented by the concentration ratio (S = C/C₀) or by the ratio of the product of the two ions concentrations in the supersaturated solution to that in the saturated one (S = ab/L_p). These σ values were lower than those obtained using the critical supersaturations at the two different solution pHs. For the present it is impossible to give a definite explanation of the results obtained. The experiments for determining the specific surface energy at the crystal-solution interface will be continued.     

The precipitation of barium chromate from aqueous solution (with rapid mixing): Kinetics of the crystal growth

The kinetics of precipitation of barium chromate from well-stirred aqueous solutions of initial solute concentrations C₀ = 0.0001 to 0.0010 M (supersaturations 8 to 80) was studied at 25 °C by conductivity measurements and chemical analysis. Nucleation occurred during induction periods and regular crystal growth then took place onto the crystallites formed during the induction periods. The crystal growth was rate-controlled, in this range, by the rate of deposition of metal salt ions onto the growing crystal surfaces. This rate, at any time, then depended on both the overall surface area (A_t) and on the residual excess solute concentration (ΔC_t) in solution according to the relation, the growth rate expressed in terms of degree of crystallisation was then The rate constant (K_α) for the crystallisation of barium chromate at 25 °C was 1.5 10⁶ sec⁻¹ M⁻².     

The precipitation of basic nickel carbonate powders from aqueous solution. Crystallite numbers,composition and final sizes

The precipitation of basic nickel carbonate hydrates was studied from nickel sulphate solutions (concentrations 0.05 M to 1 M) at 96°C, by addition of sodium carbonate, bicarbonate-carbonate and bicarbonate solutions. Precipitate compositions were determined by chemical analysis, thermogravimetric analysis, differential calorimetry and i.r. spectrophotometry; approximate final crystallite sizes and numbers were estimated from combined sedimentation and porosity measurements on precipitate aggregates. Nucleation, and then crystal growth, started after some ‘critical pH’ pH = 7.05 to 7.67 (at CO₃⁻⁻/Ni⁺⁺ ratio = 0.08–0.12); the solution pH then remained constant (until the CO₃⁻⁻/Ni⁺⁺ ratio = 0.8) and then rose to some final value. Nucleus numbers, and thence final crystallite numbers, decreased with increasing bicarbonate content of the precipitating solution and decreasing pH . Precipitate compositions did not vary significantly with reacting ion concentrations but the Ni(OH)₂/NiCO₃ ratios decreased from 2 to 1.4 with decreasing pH : thermal analysis and i.r. spectrophotometry confirmed that the final precipitates were mixtures of olated nickel carbonates and not nickel carbonate-nickel hydroxide mixtures. Final crystallite sizes of the precipitates from 1 M solutions varied approximately from 0.095 to 0.14 micron, for the above pH range.     

Molecular Association of Almotriptan with Oxalate and Terephthalate Anions

Abstract  

Crystal structures of anti-migraine drug almotriptan were crystallized with oxalic acid (I) and with terephthalic acid (II) and their crystal structures and molecular associations were determined using X-ray diffraction methods. Crystals of both (I) and (II) are monoclinic, space group P2₁/c, with a = 5.6270(4) ?, b = 27.6419(19) ?, c = 13.6228(9) ?, β = 93.057(1)°, V = 2115.9(3) ?³, Z = 4 (I) and a = 13.3756(15) ?, b = 15.6065(17) ?, c = 10.7238(12) ?, β = 98.017(2)°, V = 2216.7(4) ?³, Z = 4 (II). In almotriptan oxalate {systematic name: N,N-dimethyl-2-[5-(pyrrolidin-1-ylsulfonyl-methyl)-1H-indol-3-yl]-ethanaminium semioxalate}, C₁₇H₂₆N₃O₂S⁺, C₂HO₄ ⁻, (I) and in almotriptan hemi terephthalate hydrate {systematic name: N,N-dimethyl-2-[5-(pyrrolidin-1-ylsulfonyl-methyl)-1H-indol-3-yl]-ethanaminium hemi terephthalate monohydrate}, C₁₇H₂₆N₃O₂S⁺, 0.5(C₈H₄O₄ ²⁻), H₂O, (II), both the almotriptan cations form a trimer with the corresponding anions via N–H···O hydrogen bonds. In (I), the oxalate salt is monoprotonated and in (II), the terephthalic acid is located across the inversion centre and exists as doubly protonated anion. In (I), the cation and anion are interlinked by the N–H···O and O–H···O hydrogen bonds into continuous two-dimensional layers generate an R₆⁶(34) hydrogen-bonded motif tetramers running parallel to the (0 0 1) plane. In (II), the cation and water form a centrosymmetric tetramer of R₄⁴(22) hydrogen-bonded motif via N–H···O and O–H···O hydrogen bonds and further cross-linked by centrosymmetric anions to form an infinite three-dimensional supramolecular hydrogen-bonded networks.     

The precipitation of barium chromate powders from aqueous solution at different pHs: Nucleation,final crystal numbers and sizes

Barium chromate precipitations were studied from equivalent aqueous solutions of initial overall metal salt concentrations from 0.00013 to 0.010 M at ambient temperature and at pHs from 8 to 3. At pHs from 8 to 5, precipitation mainly occurred through homogeneous nucleation: the reciprocal induction periods (and nucleation rates) and the crystal numbers generally decreased with reduction of pH but the values at any effective mean metal salt concentration increased appreciably with increasing acidity. Presumably, both M⁺⁺A and M⁺⁺HA⁻ species were taking part in the nucleation process. – At pHs below 5, heterogeneous nucleation predominated in most precipitations: the crystal numbers and nucleus numbers at any effective metal salt concentration increased with reduction of pH in these systems. Presumably, more active sites for heterogeneous nucleation were developed.     

Kinetics of sodium fluosilicate precipitation

The formation of Na₂SiF₆ by discontinuous precipitation of dilute H₂SiF₆ with a 40% excess of an aqueous solution of NaCl under various conditions was studied. The values of induction time, number of crystals formed, their final size and their habit were determined during precipitation from solutions, whose initial supersaturation was 2 < S < 11. At S < 7–8 the crystals were formed by heterogeneous nucleation, whereas at S ≳ 7–8 homogeneous nucleation mechanism began to prevail. Once formed, the Na₂SiF₆ crystals were growing according to the screw-dislocation mechanism till they reached visible size; the corresponding values of kinetic order of nucleation and of the growth rate constant were g = 1.35 and k_g = 4.32 × 10⁻⁸ cm^2.05 sec⁻¹ g^−0.35, resp. The value of interfacial tension on the phase boundary Na₂SiF₆ crystal — saturated solution was determined (σ ∼ 52 erg/cm²). The resulting Na₂SiF₆ crystals conformed to log-normal distribution irrespective of conditions of precipitation. The dependence of the final size of crystals on supersaturation exhibited a maximum at S ∼ 6. Crystals of Na₂SiF₆ had a hexagonal habit, which was near to a spherical form at lower supersaturations, while dendritic crystals were formed at higher supersaturations.     

Nitrido-phthalocyanine-rhenium (V) structure and absorption spectra

The crystal structure of nitrido-phthalocyanine-rhenium (V) has been determined from X-ray diffraction date. The crystal data are: C₃₂H₁₆N₉Re (tetragonal), a = 1.775 nm, c = 1.386 nm, Z = 4, ϱ = 2.23 g cm⁻³. Optical and infrared absorption spectra have been measured on sublimated films and compared with the corresponding spectra of other metal phthalocyanines.     

The Chair–Envelope Conformation of Two Derivatives of Triethylammonium 3-Oxo-8,9-Dinitro-Bicyclo [3.3.1] Non-7-En-6-Nitronate [I] and [II]

Abstract  

The title compounds C₁₉H₁₈N₃O₉ ⁻·C₆H₁₆N⁺ (I) [triethylammonium 2-benzyl-2-ethoxycarbonyl-3-oxo-8,9-dinitro-bicyclo [3.3.1] non-7-en-6-nitronate] and C₁₉H₁₇N₄O₁₁ ⁻·C₆H₁₆N⁺ (II) [triethylammonium 2(4-nitrophenylmethyl)-2-ethoxycarbonyl-3-oxo-8,9-dinitro-bicyclo [3.3.1] non-7-en-6-nitronate] crystallize in monoclinic crystal system with P2 ₁ /c space group. In compounds I and II, the bicyclo [3.3.1] nonane has chair–envelope conformation. The crystal structure of compound (I) is stabilized by N–H⋯O, N–H⋯N hydrogen bonds. In both the crystal structures weak C–H⋯O hydrogen bond is observed. Both compounds adopt chair–envelope conformation. An examination of puckering parameters, torsion angles and model (Dreiding) of the title compounds clearly indicates that the ring A has slightly distorted chair conformation and ring B has slightly distorted envelope conformation.