Über hexagonale Perowskite mit Kationenfehlstellen. XXXI. Die Systeme BaO?Re2O7?MO5 mit MV = Nb,Ta

On Hexagonal Perovskites with Cationic Vacancies. XXXI. Systems BaO? Re₂O₇? M O₅ with M^V = Nb, Ta In the systems BaO? Re₂O₇? MO₅ three quaternary oxides are formed, which belong to the perovskite stacking polytypes with cationic vacancies: Ba₈Re_7/2M□₃O₂₄ (M^V = Nb, Ta; rhombohedral 24 L type; sequence (hhhhchhc)₃; space group R3 m), Ba₄Re_9/8Ta_13/8□_5/4O₁₂ (rhombohedral 12 L type; sequence (hhcc)₃; space group R3 m) and the phases Ba₅BaRe_3/2?xM □O_15?x□_x (M^V = Nb, Ta; variants of a hexagonal 5 L type).     

Über hexagonale Perowskite mit Kationenfehlstellen. XXVI. Ba12Ba2 2/3M 1/3□2O33□3 (MV = Nb,Ta) – die ersten Stapelvarianten eines rhomboedrischen 36 L-Typs

On Hexagonal Perovskites with Cationic Vacancies. XXVI. Ba₁₂Ba_{2 2/3}M _1/3□₂O₃₃□₃ (M^V = Nb, Ta) – the First Stacking Polytypes of a Rhombohedral 36 L-Type In the systems BaO? MO₅(M^V = Nb, Ta) for a Ba:M^V ratio of 2:1 polymorphism is observed. Here the low temperature modifications are described. They crystallize in a rhombohedral 36 L structure with three formula units Ba₁₂Ba_{2 2/3}M _1/3□₂O₃₃□₃ for the trigonal setting (M^V = Nb: a = 5.92₂ Å; c = 93.₂₅ Å; Ta: a = 5,92₂ Å; s = 93.4 Å).     

Zur Kenntnis des Verhaltens der Oxidsulfate der Seltenen Erden gegen Chlorwasserstoff. III. Darstellung und thermisches Verhalten der Chloridsulfate der Seltenen Erden

Treatment of chlorination products of rare earths oxidesulphates with methanol yields chloride-sulphates M^IIIClSO₄ as residues. Thermal decomposition of chloride-sulphates yields oxide-sulphates MO₂SO₄; as intermediates, mixtures of the composition MO₂SO₄? M(SO₄)₃ are obtained.     

Variable-Temperature and Variable-Pressure Kinetic and Equilibrium studies of formation and dissociation of [V(H2O)5NCS]2+

The kinetics of formation and dissociation of [V(H₂O)₅NCS]²⁺ have been studied, as a function of excess metal-ion concentration, temperature, and pressure, by the stopped-flow technique. The thermodynamic stability of the complex was also determined spectrophotometrically. The kinetic and equilibrium data were submitted to a combined analysis. The rate constants and activation parameters for the formation (f) and dissociation (r) of the complex are: k/M ^?1 · S^?1 = 126.4, k/s^?1 = 0.82; ΔH /kJ · mol^?1 = 49.1, ΔH/kJ · mol^?1 = 60.6; ΔS/ J·K^?1·mol^?1= ?39.8, ΔSJ·K^?1·mol^?1 = ?43.4; ΔV/cm³·mol^?1 = ?9.4, and ΔV/cm³ · mol^?1 =?17.9. The equilibrium constant for the formation of the monoisothiocynato complex is K²⁹⁸/M ^?1 = 152.9, and the enthalpy and entropy of reaction are ΔH⁰/kJ · mol^?1 = ? 11.4 and ΔS⁰/J. K^?1mol^?1 = +3.6. The reaction volume is ΔV⁰/cm³· mol^?1 = +8.5. The activation parameters for the complex-formation step are similar to those for the water exchange on [V(H₂O)₆]³⁺ obtained previously by NMR techniques. The activation volumes for the two processes are consistent with an associative interchange, I_a, mechanism.     

Über hexagonale Perowskite mit Kationenfehlstellen. XVI Die rhomboedrischen 12 L-Stapelvarianten Ba3AIIIM□O12 mit MV = Nb,Ta

On Hexagonal Perovskites with Cationic Vacancies. XVI. Rhombohedral 12 L-Stacking Polytypes Ba₃A^IIIM □O₁₂ with M^V = Nb, Ta The white quaternary oxides Ba₃LaM□O₁₂ with M^V = Nb, Ta belong to the group of hexagonal perovskites with cationic vacancies. They crystallize in a rhombohedral 12 L-structure (sequence (hhcc)₃; space group R3 m) with a = 5.75₁ Å; c = 28.1₁ Å (M^V = Nb); a = 5.74₆ Å; c = 28.2₀ Å (Ta) and Z = 3. Signs for the formation of isotypic compounds with A^III = Pr, Nd could be obtained as well.     

Control of Oxidation States of Transition Elements (Cr,Mn) in Nitridometalates and the Solid Solution Series Li6(Ca1‐xSrx)2[Mn2N6]

The formation of ternary nitridometalates from the elements in the case of the systems Li—Cr, V, Mn—N leads to compounds which contain the transition metals in the highest (V^V, Cr^VI) or a comparably high (Mn^V) oxidation state. In the corresponding calcium and strontium systems, the transition metals show a lower oxidation state (V^III, Cr^III, Mn^III). Transition metals with intermediate oxidation states (Cr^V, Mn^IV) are present in the quaternary (mixed cation) compounds Li₄Sr₂[CrN₆], Li₆Ca₂[MnN₆], and Li₆Sr₂[MnN₆] (R3¯(#148), a = 585.9(3) pm, c = 1908.6(4) pm, Z = 3), as well as in the solid solution series Li₆(Ca_1—xSr_x)₂[MnN₆].     

Über hexagonale Perowskite mit Kationenfehlstellen. XXIV. Rhomboedrische 9 L-Stapelvarianten in den Systemen Ba3W M □ O9−x/2□x/2 mit MV = Nb,Ta

On Hexagonal Perovskites with Cationic Vacancies. XXIV. Rhombohedral 9 L Stacking Polytypes in the Systems Ba₃W M □O_9?x/2□_x?2 with M^V = Nb, Ta In the system Ba₃WNb□O_9?x/2□_x/2 stacking polytypes of rhombohedral 9 L type (sequence (hhc)₃; space group R3 m) can be prepared with ～1/3 ? × ? 2. For x = 2(Ba₃Nb₂□O₈□) two modifications are formed. In the corresponding Ta system the phase with is reduced to a smaller region with x ? 1/3.     

Ab initio studies of negative ion-molecule(s) clusters present in the atmosphere. II. OH−(H2O)n for n = 0, 2, 3, 4

Ab initio calculations are performed with 6–31G basis set to study the geometry and binding of the H₃O, H₅O, H₇O, and H₉O complexes. The H₃O complex is also investigated with the 6–31 G* basis set and MP 2 (Moller–Plesset perturbation theory of second order).     

Über geordnete Perowskite mit Kationenfehlstellen. X. Verbindungen vom Typ ABB□1/4MVIO6 ≙ ABIIB□MO24 mit AII,BII = Ba,Sr, Ca und MVI = U,W

On Ordered Perovskites with Cationic Vacancies. X. Compounds of Type A B B □_1/4M^VIO₆ ? A B^IIB □M O₂₄ with A^II, B^II = Ba, Sr, Ca and M^VI = U, W Perovskites of type Ba₈B^IIB₂^III□UO₂₄ show polymorphic phase transformations of order disorder type. An 1:1 ordered orthorhombic HT form is transformed into a higher ordered LT modification with a fourfold cell content (four formula units Ba₈B^IIB□U₄O₂₄), compared to cubic 1:1 ordered perovskites A₂BMO₆. In the series Ba₈BaB□W₄O₂₄ and Sr₈SrB□W₄O₂₄ different ordering phenomena are observed. In comparison with 1:1 ordered cubic perovskites A₂BMO₆, the cell contains eight formula units AB^IIB□W₄O₂₄. The higher ordered cells with U^VI and W^VI are face centered, which has its origin in an ordering of cationic vacancies.     

Kinetics and mechanism of Oxidation of Diaqua(nitrilotriacetato)cobaltate(II) by Peroxodisulfate ion in aqueous acidic solutions

Kinetik und mechanismus der oxydation von diaqua(nitrilotriacetato)-cobaltat(II) durch peroxodisulfat in wäßrigsauren lösungen Die Kinetik der Oxydation von Co^II-NTA durch Peroxodisulfat (S₂O) in saurem Medium photometrisch untersucht. Die Stöchiometrie der Reaktion ist: 2Co^II-NTA^? + S₂O → 2Co^III?NTA + 2SO. Im pH-Bereich 4,2—5,4 folgt die Reaktion dem Geschwindigkeitsgesetz [H⁺] und [S₂O] sind die Wasserstoff- bzw. Peroxodisulfationen-Konzentration, K_H ist die Dissoziationskonstante des Co^II(NTA)H und k_H ist die Geschwindigkeitskonstante für den Elektronenübergang. Die Aktivierungsparameter werden mitgeteilt und der mögliche Mechanismus für den Elektronenübergang wird diskutiert.     

Cadmium in tetragonal pyramidaler Koordination im Barium-Cadmium-Oxovanadat: Ba2Cd3(VO4)2(V2O7)

Cadmium in Square Pyramids of Oxygen in the Barium Cadmium Oxovanadate: Ba₂Cd₃(VO₄)₂(V₂O₇) Single crystals of Ba₂Cd₃(VO₄)₂(V₂O₇) have been prepared by crystallization of a melt of BaCO₃, CdO and V₂O₅. It shows orthorhombic symmetry, space group D? P2₁2₁2₁, a = 7.206(2), b = 9.978(1), c = 19.617(3) Å, Z = 4. The crystal structure is characterized by (VO₄)^3? and (V₂O₇)^4? groups, CdO₆ octahedra, BaO₁₂ and BaO₉ polyhedra and with respect to Cd containing oxides unusual square pyramids of O^2? around Cd²⁺. The observed [CdO₄] zickzack chains are connected by VO₄ tetrahedra, V₂O₇ double tetrahedra and CdO₅ pyramids, forming a tunnel structure along [100]. The tunnels are filled by barium.     

Low Valence States of Metal Chelates. V. Tris(1,10-phenanthroline)cobalt(II) and bis(2,9-dimethyl-1,10-phenanthroline)cobalt(II) perchlorates

D. C. polarography and cyclic voltammetry were used for investigating the reduction processes of the tris(1,10-phenanthroline)cobalt(II) and bis(2,9-dimethyl-1, 10-phenanthroline)-cobalt(II) perchlorates in 0.1 M solutions of tetraethylammonium perchlorate in acetonitrile. The first complex gave a four-step reduction wave; the first two steps were found to be diffusion controlled and reversible reductions from Co(phen)⁺ to Co(phen)₃⁺ to Co(phen) to Co(phen;) occured. The second complex gave a six-step reduction wave; the first three steps were found to be diffusion controlled and were to be considered as successive reversible reductions from Co(2, 9dm-phen)⁺ to Co(2, 9dmphen), from Co(2, 9dmphen) to Co(2, 9dmphen)₂ and from Co(2, 9dmphen)₂ to Co(2, 9dmphen).     

Sur la Stoechiométrie de la Variété Allotropique γ de Bi2O3

On the Stoichiometry of the Allotropic Variation γ-Bi₂O₃ The study of the solid solutions Bi₁₂[BBi□_1/5]O₂₀ (B^+V = As, V) with 0 ? x ? 0,80 leads for x = 0,77 to a phase whose cubic centered symmetry and parameter (10.255 Å) correspond to those previously announced for γ-Bi₂O₃. The présence of impurities seems required to obtain such a phase whose theoretical stoichiometry should be Bi₁₂[Bi□_1/5]O₂₀ i. e. Bi₂O_3,125.     

Complexes of Silver(l) with arsenic and phosphorus donor ligands. Co-ordination number 4

Some tetracoordinated complexes having the formulae, [AgL₄]X (L = Triphenyl-arsine; X = NO, ClO and BrO) and [AgL₃X] (L = Triphenyl-arsine/phosphine; X = SCN^? and NCO^?) have been prepared and characterised by analyses, conductance, magnetic susceptibility and infra-red spectroscopy.     

Photoinduced electron transfer from polystyrene pendant tris(2,2′-bipyridyl)ruthenium (II) complex to methylviologen

The characteristics of the photoinduced electron transfer reaction from polystyrene pendant tris(2,2′-bipyridyl)ruthenium (II) complex [Ru(bpy)] to methylviologen (MV²⁺) were studied. The rate constant k₁ from the excited state of the complex, Ru(bpy), to MV²⁺ were determined for both the polymeric and monomeric complexes from the lifetime τ of Ru(bpy) and the quenching rate of Ru(bpy) by MV²⁺. The polymer pendant Ru(bpy) showed three kinds of τ components ranging from 7 to 474 ns, in contrast to the monomeric complex, which showed one component of 350 ns. The k₁ values for both complexes were almost the same, on the order of 10⁸ L/mol s. The photoinduced electron transfer from solid-phase Ru(bpy) to liquid-phase MV²⁺ was realized by utilizing the polymer complex, and the solid–liquid interphase reaction system is discussed.     

63Cu-NMR.-Untersuchungen von Kupfer (I)-Tetrapyridin-und Kupfer (I)-Tetraacetonitrilsolvaten

⁶³Cu-NMR.-Spectra of Cu(CH₃CN)₄X (X = ClO, BF, PF) and Cu(C₅H₅N)₄X (X = ClO, BF) in solution are reported at different temperatures and concentrations. The influence of temperature on the linewidth and chemical shift indicates an equilibrium of Cu(CH₃CN) and Cu(C₅H₅N) with another complex of lower symmetry. The preferential solvation of Cu (I) by pyridin in a mixture acetonitrile/pyridine is clearly shown.     

Darstellung und spektroskopische Charakterisierung von Fluoro-Chloro-Iridaten(V)

Preparation and Spectroscopic Characterization of Fluoro-Chloro-Iridates(V) By careful oxidation of the pure fluoro-chloro iridates(IV) with BrF₃ in dichloromethane the corresponding pentavalent complexes [IrF₅Cl]^?, cis-[IrF₄Cl₂]^?, and fac-[IrF₃Cl₃]^? are formed without replacements of Cl ligands. The vibrational spectra of these mixed ligand complexes are assigned according to point groups C_4v, C_2v, and C_3v. The increased bond strength compared with the corresponding Ir^IV compounds is indicated by a significant shift to higher energy by about 5–15%. The anomalous intensities of some of the Raman active fundamentals are attributed to the resonance Raman effect. The electronic absorption spectra are measured on the solid tetraethylammonium salts of the fluoro-chloro iridates(V) at 10 K. The strong bands in the UV/VIS region are assigned to charge transfer transitions from π(t_1u, t_2u) and σ(t_1u) Cl orbitals into the π(t)Ir^V level. The intraconfigurational transitions within the t configuration of Ir^V are split by spin orbit coupling and lowered symmetry, observed in the ranges 3000, 5100–6400, 10900–13000, and 18200 cm^?1. The O? O transitions are deduced from the vibrational fine structure; in some cases they are confirmed by electronic Raman bands. With increasing number of F ligands all absorption bands are shifted systematically to higher energies.     

Electron transfer reactivity of O2+O system in low-spin coupling: Ab Initio study at electron correlation level

The electron transfer reactivity of the O₂+O system in low-spin coupling is studied at the second-order unrestricted Møller–Plesset (full)/6-311+G* basis set level by using different transition state structures. The properties and stabilities of the encounter complexes are compared for the five selected coupling structures: two T type, collinear, parallel, and crossing. The activation barriers and the coupling matrix elements are also calculated. The results indicate that the structures of the encounter complexes directly affect the electron transfer mechanism and rate. These encounter complexes are structurally unstable, the contact distances between the acceptor O₂ and the donor O are generally large, the interaction is weak, and the structures are floppy. The electronic transmission factor for the reacting system, O₂+O, is less than unity; thus, the electron transfer reaction is nonadiabatic in nature. Analysis of the dependence of relevant kinetic parameters on various influencing factors has shown that the effect of the solvent medium on the coupling matrix element is small but that on the electron transfer rate is very large. Among the five selected transition state structures, the electron transfer is more likely to take place via T₁-type and P-type structures. In the low-spin coupling the favorable electronic states for two reacting species are ¹∑(O₂) and X²Π_g(O) instead of X³∑(O₂) and X²π_g(O), which are favorable for the high-spin (quartet state) coupling mechanism. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 989–998, 1999     

The kinetics of the interaction of peroxy radicals. I. The Tertiary Peroxy Radicals

Existing data on the self-reactions of tertiary peroxy radicals RO₂ has been reanalyzed and corrected to deduce Arrhenius parameters for both termination and nontermination paths. For R = t-Butyl, these are logk_t(M^?1sec^?1) = 7.1 - (7.0/θ) and logk_nt(M^?1sec^?1) = 9.4 - (9.0/θ), respectively, different from those recommended by other authors. The higher magnitudes observed for termination processes of tertiary peroxy radicals like those of cumyl and 1,1-diphenylethyl have been discussed in terms of a much greater cage recombination of cumyloxy radicals as contrasted with t-butoxy radicals. It is shown that for benzyl peroxy radicals, the R—O bond dissociation energy is sufficiently low (18–20 kcal) that reversible dissociation into R^˙ + O₂ opens a competing second-order path to fast recombination R^˙ + RO → ROOR. This path is probably not important for cumyl peroxy radicals under usual experimental conditions but can become important for 1,1-diphenyl ethyl peroxy radicals at (O₂) < 10^?3M. At very low RO concentrations (<10^?5M), in the absence of added O₂, an apparent first-order disappearance of RO can occur reflecting the rate determining breaking of the cumyl—O bond followed by the second step above. The thermochemistry of RO is used to show that the reaction of R₂O₄ → 2RO + O₂ must be concerted and cannot proceed via RO which is too unstable and cannot form even from RO^˙ + O₂.     

Interactions Magnetiques dans quelques Ferrites Oxyfluores a Structure Spinelle de Formule ZnxMFe2−xO4–xFx (M ? Fe,Co, Ni)

Magnetic interactions in some oxyfluoroferrites of spinel structure with the formula Zn_xMe_2?xO_4?xFx (M = Fe, Co, Ni) Whereas the ferromagnetic spin arrangement of the B-cations is not modified by the Zn²⁺?Fe³⁺ substitution in the ZnFe[Fe₂₊Fe³⁺]O_4?xF_x (0 ≤ x ≤ 0,50) spinel, this same substitution leads to a spin canting in the ZnFe[Co₂₊Fe³⁺]O_4?xF_x and ZnFe[Ni₂₊Fe³⁺]O_4?xF_x (0 ≤ x ≤ 0,80) simples. The difference in the magnetic behaviors with regard to the AB and BB interactions can be explained on the basis of the magnetic exchange theory.