Identification of Saturating Solid Phases in the System Ce2(SO4)3-H2O from the Solubility Data

Saturating solid phases, Ce₂(SO₄)₃·hH₂O, with hydrate numbers h equal to 12, 9, 8, 5, 4 and 2, have been identified by critical evaluation of the solubility data in the system Ce₂(SO₄)₃—H₂O over the temperature range 273–373 K. The results are compared with the respective TG—DTA—DSC and X-ray data. The solubility smoothing equations, transition points and solution enthalpy estimators of the identified hydrates are given. The stable equilibrium solid phases are concluded to be only Ce₂(SO₄)₃·9H₂O at 273–310 K, Ce₂(SO₄)₃·4H₂O at 310–367 K and Ce₂(SO₄)₃·2H₂O at 367–373 K. Divergencies of up to 185% in the reported solubility data are mainly due to a variety of metastable equilibria involved in the close crystallization fields, and incorrect assignments of the saturating solid phases. Since a similar variety of the hydrate numbers exists for the analogous La(III) system, it most probably also occurs for the corresponding Pu(III), Np(III) and U(III) systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal properties and thermochemistry of lanthanide chromates

The behavior of chromates Ln₂(CrO₄)₃·7H₂O and Rb₅Ln(CrO₄)₂ (Ln = La, Pr, Nd, Sm, and Gd) was studied by derivatography as they were heated in air in a temperature interval of 300–1470 K. The high temperature enthalpies of LaCrO₃ and YCrO₃ at 865–1350 K and enthalpies of solution of La₂(CrO₄)₃·7H₂O in a solution of nitric acid at 298 K were measured by calorimetric methods. The standard enthalpies of formation were calculated for some compounds of composition Ln₂(CrO₄)₃·2H₂O and LnCrO₃.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 290–295, February, 2005.     

Isopiestic determination of the osmotic and activity coefficients of aqueous Lu2(SO4)3 at 25°C

Osmotic coefficients have been measured for aqueous Lu₂(SO₄)₃ solutions from 0.12402 to 0.89631 mol-kg^–1 at 25°C by use of the isopiestic method; these measurements extend into the supersaturated molality region. Since there was a lack of activity data for Lu₂(SO₄)₃ solutions at lower molalities, they were approximated by equating them to results for La₂(SO₄)₃ from freezing temperature depression measurements. The combined osmotic coefficients were then used to derive mean molal activity coefficients for Lu₂(SO₄)₃ solutions. The osmotic coefficients decrease to 0.307 as their minimum value and the mean molal activity coefficients decrease to 0.0069. When these activities were combined with our previously reported solubility of 0.6260±0.0017 mol-kg^–1 for Lu₂(SO₄)₃·8H₂O, a thermodynamic solubility product of 2.3×10^–10 was obtained. This value yields the Gibbs energy of formation G _f ^° (Lu₂(SO₄)₃·8H₂O, cr)=–5518.9±16.4 kJ-mol^–1.     

Über einen Isokonzentrationsschnitt in bezug auf Schwefelsäure im Dreistoffsystem Ammoniumsulfat-Eisen(III)sulfat-Wasser bei 25 °C

Zusammenfassung Untersucht wird ein Isokonzentrationsschnitt in bezug auf Schwefelsäure im Dreistoffsystem (NH₄)₂SO₄–Fe₂(SO₄)₃–H₂O bei 25 °C. Es wird ein Kristallisationsbereich von anomalen Mischkristallen auf der Basis (NH₄)₂SO₄ bei einem Eisen(III)-sulfatgehalt von 1,5% des Ammoniumsulfatgehalts ermittelt. Außerdem wird ein Kristallisationsbereich von Mischkristallen auf der Basis NH₄Fe(SO₄)₂·12 H₂O, ein Kristallisationsbereich von reinem NH₄Fe(SO₄)₂·12 H₂O und ein Kristallisationsbereich von Fe₂(SO₄)₃·9 H₂O festgestellt. Die Anwesenheit von Schwefelsäure in der Lösung vermindert die Löslichkeit aller Phasen im obigen System.Untersucht wird teilweise das Dreistoffsystem NH₄Fe(SO₄)₂–H₂SO₄–H₂O bei 25 °C. Es wird ein Kristallisationsbereich von NH₄Fe(SO₄)₂·12 H₂O, welches als feste Phase bis etwa 12% Schwefelsäure in der Lösung existiert, ermittelt. Es wird bewiesen, daß die anomalen Mischkristalle auf der Basis (NH₄)₂SO₄ metastabile, mit der Zeit langsamen Veränderungen unterliegende Systeme sind.

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An isoconcentration section with respect to sulphuric acid of the ternary system ammonium sulphate-ferric sulphate-water at 25 °C

The system (NH₄)₂SO₄–Fe₂(SO₄)₃–H₂O was investigated at 25 °C with an excess of H₂SO₄. The crystallization ranges of the anomalous mixed crystals based on ammonium sulphate, the mixed crystals on the basis of the double-salt NH₄Fe(SO₄)₂· ·12 H₂O, the crystallization ranges of Iron(III)-ammonium sulphate and Fe₂(SO₄)₃·9 H₂O were determined. The presence of H₂SO₄ in the solution lowers the solubilities of the different phases occurring in the said system. The system NH₄Fe(SO₄)₂–H₂SO₄–H₂O was partially studied at 25 °C. The crystallization range of iron-ammonium alum existing as a solid phase at equilibrium at sulphuric acid concentrations up to ca. 12% in the solution is described. It was shown that the anomalous mixed-crystals based on ammonium sulphate undergoe slow changes with time.

     

A New Predictive Equation for the Surface Tensions of Aqueous Mixed Ionic Solutions Conforming to the Linear Isopiestic Relation

The linear isopiestic relation has been used, together with the fundamental Butler equations, to establish a new simple predictive equation for the surface tensions of the mixed ionic solutions. This newly proposed equation can provide the surface tensions of multicomponent solutions using only the data of the corresponding binary subsystems of equal water activity. No binary interaction parameters are required. The predictive capability of the equation has been tested by comparing with the experimental data of the surface tensions for the systems HCl–LiCl–H₂O, HCl–NaClO₄–H₂O, HCl–CaCl₂–H₂O, HCl–SrCl₂–H₂O, HCl–BaCl₂–H₂O, LiCl–NaCl–H₂O, LiCl–KCl–H₂O, NaCl–KCl–H₂O, KNO₃–NH₄NO₃–H₂O, and LiCl–NaCl–KCl–H₂O at 298.15 K; KNO₃–NH₄Cl–H₂O, KBr–Sr(NO₃)₂–H₂O, NaNO₃–Sr(NO₃)₂–H₂O, NaNO₃ –(NH₄)₂SO₄–H₂O, KNO₃–Sr(NO₃)₂– H₂O, NH₄Cl–Sr(NO₃)₂–H₂O, NH₄Cl– (NH₄)₂SO₄–H₂O, KBr–KCl–H₂O, KBr–KCl–NH₄Cl–H₂O, KBr–KNO₃– Sr(NO₃)₂–H₂O, KBr–NH₄Cl–Sr(NO₃)₂–H₂O, KNO₃–NH₄Cl–Sr(NO₃)₂–H₂O, and NH₄Cl–(NH₄)₂SO₄–NaNO₃–H₂O at 291.15 K; and KBr–NaBr–H₂O at temperatures from 283.15 to 308.15 K. The agreement is generally quite good.     

Aqueous Solution Chemistry of Scandium(III) Studied by Raman Spectroscopy and ab initio Molecular Orbital Calculations

Aqueous solutions of Sc(ClO₄)₃,ScCl₃, and Sc₂(SO₄)₃ were studied by Ramanspectroscopy over a wide concentration range. In aqueous perchlorate solutionSc(III) occurs as an hexaaqua cation. The weak, polarized Raman band assignedto the ₁(a _1g) ScO₆ mode of the hexaaqua-Sc (III) ion has been studied as afunction of concentration and temperature. The ₁(a _1g) ScO₆ mode at 442 cm^–1of the hexaaqua—Sc(III) shifts only 3 cm^–1 to lower frequency and broadensabout 20 cm^–1 for a 60°C temperature increase. The Raman spectroscopic datasuggest that the hexaaqua-Sc (III) ion is stable in perchlorate solution within theconcentration and temperature range measured. Besides the polarized componentat 442 cm^–1, two weak depolarized modes at 295 and 410 cm^–1 were measuredin the Raman effect. These two modes of the ScO₆ unit were assigned to ₃(f _2g)and ₂(e ), respectively. The infrared active mode ₃(f _1u) was measured at 460cm^–1. The frequency data confirm the centrosymmetry of the Sc(III) aquacomplex, contrary to earlier Raman results. The powder spectrum of crystallineSc(ClO₄) ₃ · 6H₂O shows the above described Raman modes as well. Thesefindings are in contrast to Sc₂(SO₄)₃ solutions, where sulfate replaces water inthe first hydration sphere and forms thermodynamically strong sulfato complexes.In ScCl₃ solutions thermodynamically weak chloro complexes could be detected.Ab initio molecular orbital calculations were performed at the HF and MP2 levelsof theory using different basis sets up to 6–31 + G(d). Gas-phase structures,binding energies, and enthalpies are reported for the Sc³⁺(OH₂)₆ and Sc³⁺(OH₂)₇cluster. The Sc—O bond length for the Sc³⁺(OH₂)₆ cluster reproduces theexperimentally determined bond length of 2.18 Å (recent EXAFS data) almost exactly.The theoretical binding energy for the hexaaqua Sc(III) ion was calculated andaccounts for ca. 54–59% of the experimental hydration enthalpy of Sc(III). Thethermodynamic stability of the Sc³⁺(OH₂)₆(OH₂) cluster was compared to thatof the Sc³⁺(OH₂)₇ cluster, demonstrating that hexacoordination is inherently morestable than heptacoordination in the scandium (III) system. The calculated ₁ScO₆frequency of the Sc⁺(OH²)⁶ cluster is ca. 12% lower than the experimentalfrequency. Adding an explicit second hydration sphere to give Sc³⁺ (OH²)¹⁸,denoted Sc[6 + 12], is shown to correct for the discrepancy. The frequencycalculation and the thermodynamic parameters for the Sc[6 + 12] cluster aregiven and the importance of the second hydration sphere is stressed. Calculatedfrequencies of the ScO₆ subunit in the Sc[6 + 12] cluster agree very well withthe experimental values (for example, the calculated ₁ScO₆ frequency was foundto be 447 cm^–1, in excellent agreement with the above-reported experimentalvalue). The binding enthalpy for the Sc[6 + 12]cluster predicts the single ionhydration enthalpy to about 89%.     

Hydrogen-Bonded Aggregates of Scandium(III) Complexes

The influence of the concentration of halide ions and concentration of an organic component (Solv) in solutions on the composition, coordination number, and structure of the scandium(III) complexes in solutions and in crystal is studied. The ⁴⁵Sc NMR data show that the main factor determining Cl^– coordination in the Sc³⁺–Cl^––H₂O–Solv systems is the Solv concentration. According to the X-ray diffraction analysis data, at the molar ratios of X^– : Sc³⁺ < 3 (X^– = Cl, Br), the [Sc(OH)(H₂O)₅]₂X₄ · 2H₂O salts with a coordination number of Sc 7 are isolated from solutions in H₂O and alcohols (coordination core is ScO₇ and X^– ions are not involved in coordination). Supramolecular H-bonded aggregates containing the ScCl₃(H₂O)₃ molecular complex with coordination number of Sc 6 and meridianal arrangement of analogous ligands are isolated from solutions with the Cl^– : Sc³⁺ molar ratios from 3 to 20 (in concentrated HCl) using macrocyclic molecules (1,4,7,10,13,16-hexaoxocyclooctadecane (18C6) and 1,4,10,13-tetraoxo-7,16-diazacyclooctadecane (DA18C6)).     

Solubility of some lanthanide sulfates in polycomponent systems containing H2SO4

Summary The paper presents data on the solubility of La, Ce, Pr, Nd sulfates in the polycomponent system La₂(SO₄)₃·8H₂O-Ce₂(SO₄)₃·8H₂O-Pr₂(SO₄)₃·8H₂O-Nd₂(SO₄)₃· 8H₂O-H₂SO₄-H₂O (at 25°C and 64°C) as well as in the same polycomponent system but in the presence of CaSO₄·2H₂O. The solubility of the sulfates — ocathydrates of Pr at 25°C and 64°C and of La and Ce at 64°C in tricomponent systemLn ₂(SO₄)₃·8H₂O-H₂SO₄-H₂O are also reported.

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Löslichkeit einiger Lanthanidsulfate in Mehrkomponenten-Systemen mit H₂SO₄

Zusammenfassung Die Arbeit präsentiert Daten für die Löslichkeit von La-, Ce-, Pr- und Nd-Sulfaten in den Vielkomponenten-Systemen La₂(SO₄)₃·8H₂O-Ce₂(SO₄)₃·8H₂O-Pr₂(SO₄)₃·8H₂O-Nd₂(SO₄)₃· 8H₂O-H₂SO₄-H₂O (bei 25°C und 64°C) sowie in den gleichen Systemen, jedoch in Anwesenheit von CaSO₄·2H₂O. Über die Löslichkeit von Sulfatoctahydraten von Pr bei 25°C und 64°C und von La und Ce bei 64°C in den Dreikomponenten-SystemenLn ₂(SO₄)₃·8H₂O-H₂SO₄-H₂O wird auch berichtet.

     

Thick rhodium electrodeposition on copper backing as the target for production of palladium-103

The Rh target preparation for production of ¹⁰³Pd was investigated by using a thick electrodeposition of rhodium metal on a copper backing. The electrodeposition experiments were performed in acidic sulfate media using RhCl₃·3H₂O, Rh₂(SO₄)₃ (recovered from hydrochloric acid solution) and also in the commercially available Rhodex plating baths. For high current beam irradiation of a Rh target, the qualities of the deposit of the three baths were compared in terms of thermal shock, crack-free and morphology criteria. The quality of the plating obtained from a sulfate bath [Rh₂(SO₄)₃] was comparable with the one obtained from commercially available Rhodex bath. The optimum conditions of the electrodepositions were as follows: 4.8 g rhodium [as Rh₂(SO₄)₃], pH 2, DC current density of ca 8.5 mA·cm^–2, 1% sulfamic acid (w/v) and temperature 40–60 °C.The authors would like to thank their colleagues at the VUB-Cyclotron department for help and assistance in preparation of the electrodeposition equipment and taking the SEM photomicrographs and also K. Aardaneh (NRCAM) for his assistance.     

Thick rhodium electrodeposition on copper backing as the target for production of palladium-103

The Rh target preparation for production of ¹⁰³Pd was investigated by using a thick electrodeposition of rhodium metal on a copper backing. The electrodeposition experiments were performed in acidic sulfate media using RhCl₃·3H₂O, Rh₂(SO₄)₃ (recovered from hydrochloric acid solution) and also in the commercially available Rhodex plating baths. For high current beam irradiation of a Rh target, the qualities of the deposit of the three baths were compared in terms of thermal shock, crack-free and morphology criteria. The quality of the plating obtained from a sulfate bath [Rh₂(SO₄)₃] was comparable with the one obtained from commercially available Rhodex bath. The optimum conditions of the electrodepositions were as follows: 4.8 g rhodium [as Rh₂(SO₄)₃], pH 2, DC current density of ca 8.5 mA·cm^–2, 1% sulfamic acid (w/v) and temperature 40–60 °C.The authors would like to thank their colleagues at the VUB-Cyclotron department for help and assistance in preparation of the electrodeposition equipment and taking the SEM photomicrographs and also K. Aardaneh (NRCAM) for his assistance.     

Mixed Complex Salt [Cu4(SCN2H4)7(NO3)](NO3)(SO4) · 3.3H2O: Synthesis and X-Ray Diffraction Analysis

The complex salt [Cu₄(SCN₂H₄)₇(NO₃)](NO₃)(SO₄) · 3.3H₂O was synthesized via reaction of aqueous solutions of thiourea with copper nitrate at 80°C and studied using X-ray diffraction analysis. The conditions and reasons for the partial oxidation of thiourea to sulfate ions were established. The crystals are monoclinic: a = 12.6072(7) Å, b = 15.4265(8) Å, c = 22.108(1) Å, = 120.133(6)°, space group P2₁/c, Z = 4. The crystal structure consists of [Cu₄(SCN₂H₄)₇(NO₃)]³⁺ complex cations, SO₄ ^2–, and NO₃ ^– anions, and molecules of the water of crystallization. Three types of coordination of the Cu atom were distinguished in the structure: trigonal (Cu–S 2.213–2.279 Å), tetrahedral (Cu–S 2.315–2.459 Å), and trigonal–pyramidal (3+1) (Cu–S 2.26–2.288, Cu–O 2.68 Å). The NO₃ ligand was found to be orientationally disordered.     

An aqueous thermodynamic model for a high valence 4∶2 electrolyte Th4+−SO 4 2− in the system Na+−K+−Li+−NH 4 + −Th4+−SO 4 2− −HSO 4 − −H2O to high concentration

An aqueous thermodynamic model that is valid from zero to high concentration is proposed for the Na⁺–K⁺–Li⁺–NH ₄ ⁺ –Th⁴⁺–SO ₄ ^2– –HSO ₄ ^– –H₂O system. The model is based on the aqueous ion-interaction model of Pitzer and coworkers. The thorium sulfate complex species Th(SO₄)₂(aq) and Th(SO₄) ₃ ^2– are also included in the model. The final thermodynamic model presented here accurately predicts all reliable thermodynamic data, including solvent extraction and solubility data, for the Na⁺–K⁺–Li⁺–NH ₄ ⁺ –Th⁴⁺–SO ₄ ^2– –HSO ₄ ^– –H₂O system to high concentration. The aqueous thermodynamics of high-valence (3:2, 4:2), electrolytes are complicated by very strong specific ion interactions or ion pairing in dilute solution and by an effective redissociation of aqueous complex species at high concentration. Methods of treating these complications, in terms of valid aqueous thermodynamic models, are discussed in detail for the high-valence Th⁴⁺–SO ₄ ^2– –H₂O system.     

Osmium(VIII) mediated oxidation of mercury(I) by cerium(IV) in aqueous sulphuric acid – a kinetic and mechanistic study

The oxidation of Hg^I by Ce^IV has been studied in aqueous H₂SO₄. A minute amount (10^–6 mol dm^–3) of Os^VIII is sufficient to catalyse the reaction. The active catalyst, substrate and oxidant species are H₂OsO₅, [Hg₂(SO₄)HSO₄]^– and H₃Ce(SO₄)^– ₄, respectively. Possible mechanisms are proposed and the reaction constants involved have been determined.     

Reduction of nitrobenzene in the liquid phase by carbon monoxide (II) in the presence of palladium complexes

Conclusions We investigated the transformations of catalysts based on palladium complexes under the conditions of the catalytic reduction of nitrobenzene by carbon monoxide (II). We established that the reduced forms of the catalyst are Pd₂(PPh₃),₄(CO)·H₂SO₄ and Pd₂PPh₃)₄CO)· HClO₄, while the reduced forms are Pd(PPh₃)₂SO₄ and Pd(PPh₃)₃(H₂O)(ClO₄)₂ in the sulfate and the perchlorate media, respectively.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 998–1002, May, 1989.     

New Structure Type among Octahydrated Rare‐Earth Sulfates, β‐Ce2(SO4)3·8H2O,and a new Ce2(SO4)3·4H2O Polymorph

Syntheses, crystal structures and thermal behavior of two new hydrated cerium(III) sulfates are reported, Ce₂(SO₄)₃·4H₂O ( I ) and β‐Ce₂(SO₄)₃·8H₂O ( II ), both forming three‐dimensional networks. Compound I crystallizes in the space group P2₁/n. There are two non‐equivalent cerium atoms in the structure of I , one nine‐ and one ten‐fold coordinated to oxygen atoms. The cerium polyhedra are edge sharing, forming helically propagating chains, held together by sulfate groups. The structure is compact, all the sulfate groups are edge‐sharing with cerium polyhedra and one third of the oxygen atoms, belonging to sulfate groups, are in the S–Oμ₃–Ce₂ bonding mode. Compound II constitutes a new structure type among the octahydrated rare‐earth sulfates which belongs to the space group Pn. Each cerium atom is in contact with nine oxygen atoms, these belong to four water molecules, three corner sharing and one edge sharing sulfate groups. The crystal structure is built up by layers of [Ce(H₂O)₄(SO₄)]_nⁿ⁺ held together by doubly edge sharing sulfate groups. The dehydration of II is a three step process, forming Ce₂(SO₄)₃·5H₂O, Ce₂(SO₄)₃·4H₂O and Ce₂(SO₄)₃, respectively. During the oxidative decomposition of the anhydrous form, Ce₂(SO₄)₃, into the final product CeO₂, small amount of CeO(SO₄) as an intermediate species was detected.     

Solubility in the systems Rb2SO4-H2SO4-H2O and Cs2SO4-H2SO4-H2O at 25°

Conclusions The solubility of rubidium and cesium sulfates in aqueous solutions of sulfuric acid was studied at 25°. Rubidium sulfate forms the compounds 3Rb₂SO₄· H₂SO₄, Rb₂SO₄ · H₂SO₄, Rb₂SO₄·3H₂SO₄ and Rb₂SO₄·7H₂SO₄ with sulfuric acid, while cesium sulfate forms the compounds Cs₂SO₄·H₂SO₄; Cs₂SO₄·3H₂SO₄ and Cs₂SO₄ · 7H₂SO₄.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1166–1170, June, 1968.     

Thermal and X-Ray studies of reactions between scandium(III) oxide and sodium or potassium persulfates

TG, DTG, and DTA experiments were carried out to elucidate the influence of Sc₂O₃ on the thermal decomposition of Na₂S₂O₈ and K₂S₂O₈ under a static (air) atmosphere from ambient to 1050°C, using a derivatograph. X-Ray diffractometry has been employed to identify the intermediate and final decomposition products. Different Sc₂O₃ Na₂(K₂)S₂O₈ molar ratios were investigated and the 1 : 3 ratio found to be the one that gives stoichiometric reactions with either of these salts. Sc₂O₃ was found to react at 250 and 440°C with the thermally produced Na₂S₂O₇ yielding Sc₂(SO₄)₃. The scandium(III) sulfate was thermally stable up to 840°C. Similarly, the oxide reacts stoichiometrically at 420°C to produce KSc(SO₄)₂, a double salt which began to decompose at 840°. Moreover, three new crystalline phase-transformations were detected for Sc₂(SO₄)₃ at 640, 695, and 735°C.     

Synthetic ferric sulfate trihydrate,Fe2(SO4)3·3H2O,a new ferric sulfate salt

Ferric sulfate trihydrate has been synthesized at 403 K under hydrothermal conditions. The structure consists of quadruple chains of [Fe₂(SO₄)₃(H₂O)₃] parallel to [010]. Each quadruple chain is composed of equal proportions of FeO₄(H₂O)₂ octahedra and FeO₅(H₂O) octahedra sharing corners with SO₄ tetrahedra. The chains are joined to each other by hydrogen bonds. This compound is a new hydration state of Fe₂(SO₄)₃·nH₂O; minerals with n = 0, 5, 7.25–7.75, 9 and 11 are found in nature.     

New Copper(II) Complexes Containing 2-Furoic Hydrazide and 5-Nitro-2-Furoic Hydrazide Ligands: Synthesis,Thermal, Magnetic and Spectroscopic Characterization

Two new copper(II) complexes, [Cu₂(L¹)₄(H₂O)₂](SO₄)₄· 2H₂O and [Cu(L²)₂(H₂O)₂]SO₄, were isolated containing 2-furoic hydrazide and 5-nitro-2-furoic hydrazide ligands, respectively. The complexes were characterized by thermal, magnetic and spectroscopic techniques, showing a distorted tetragonal environment around the metal ion. Compound (1), containing 2-furoic hydrazide as the ligand, appears to be dimeric in the solid state, with substituted hydrazine acting as a bidentate bridging ligand. On the contrary, a monomeric species was observed with the 5-nitro-2-furoic hydrazide ligand, probably in the cis configuration, for compound (2). Magnetic measurements for the binuclear copper(II) complex (1) were carried out at low temperatures, in the 2–300 K range, and a magnetic field of 500 G, indicating that besides an intramolecular ferromagnetic interaction between the two Cu(II) centers, for which J/k = 1.07 K, further weak antiferromagnetic interactions between adjacent dimers, with Jz/k =–0.95 K, should be taken into account. However, in MeOH/H₂O solution, evidence of equilibria involving the dimer (1) and the corresponding mononuclear cis and trans species was obtained from e.p.r. spectra.     

The reactivity of sulfur dioxide with transition metal complexes containing 4-cyanopyridine- and 3-pyridylcarbinol-N-oxide: the high temperature isolation of a manganese(II) iodide SO2-adduct

The reactivity of metal complexes M(RPyO)_nX₂(H₂O)_m (RPyO=4-cyanopyridine-N-oxide or 3-pyridylcarbinol-N-oxide; M=Mn, Co, Cu; X=Cl, Br, I, NO₃; n=2–4 and m=0–3) with SO₂ has been studied in toluene slurries and in the solid state at room temperature and in the solid state at high temperature. Only the metal iodide precursors containing 4-CNPyO reacted with SO₂ in the solid state or in a toluene slurry but never above room temperature. Among the precursors containing 3-HOH₂CPyO, only the copper metal complexes interact with SO₂ at room temperature in toluene slurries. Surprisingly, Mn(3-HOH₂CPyO)₂I₂(H₂O) reacted with SO₂ at 210°C, whereas the metal complex was unreactive at room temperature. Likewise, Cu(3-HOH₂CPyO)₂(NO₃)₂ reacted at 100°C, the SO₂ being oxidised to sulfate, displacing the nitrate group, but not at room temperature.