Emission of secondary ions from 3d, 4d, and 5d transition metals under chloro-trifluoro-methane CClF3 as reactant gas

Surface interactions of CClF₃ with polycrystalline samples of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nb, Mo, Rh, Pd, Ag, Ta, W, Re, Ir, and Pt were investigated by means of moderate dynamic SIMS. As observed with other reactant gases these transition metals in most cases appear to be discernible into “dissociative” and (partial) “molecular” adsorbents. Small signals of oxidic secondary ions which are detectable for residual gas conditions vanished under the action of CClF₃. However, due to strong polarization by either of the halogens, the emission of Me²⁺ ions is enhanced for Ti, V, and Nb. Received: 6 August 1997 / Revised: 22 December 1997 / Accepted: 29 December 1997     

Theoretical modeling of elementary reactions of dissociative addition of an H2 molecule to aluminum clusters MAl12 doped with early 3d and 4d transition metal atoms

The potential energy surfaces (PES) of the elementary catalytic cycle of early stages of the H₂ + MAl₁₂ reaction of dissociative addition of an H₂ molecule to aluminum clusters MAl₁₂ doped with “light” 3d and 4d transition metal atoms (Sc, Y, Ti, Zr, V, Nb) in the states of different multiplicity have been calculated by the density functional theory method. The effect of the dopant nature and the electronic state multiplicity of the cluster on the energies and activation barriers of hydrogenation reactions of aluminum clusters is considered. The calculated PES corresponding to the early stages of the H₂ + TiAl₁₂ reaction does not reveal any specific features that could be evidence of the significant preference of the titanium dopant as compared with other transitions metals like Zr or W.     

Recent Advances in the Synthesis of N‐Heteroatom Substituted Imido Complexes Containing a Nitrido Bridge [M=N—E] (M = Group 4, 5 and 6 Metal,E = B,Si, Ge,P, S)

The focus of the current report lies on recent developments of synthetic methods applied to the synthesis of some high‐valent complexes containing the nitrido functionality [N]^3— as a link between a group 4, 5 or 6 transition metal and a main group element E (E = B, Si, Ge, P, S). Emphasis is put on results, that have been obtained within the “Schwerpunktprogramm “Nitridobrücken” funded by the Deutsche Forschungsgemeinschaft. The synthetic methods include condensation reactions of reactive chloro and oxo complexes (M = V, Nb, Ta, Cr, Mo, W) with silylamines, sulfonylamides, with N‐silyl and N‐lithio iminophosphoranes, furthermore methatesis reactions of oxo complexes with N‐sulfonyl sulfinyl amides (M = V, Cr, Mo, W), the oxidative addition of element azides to d² metal centers (M = V, W), and finally transamination reactions of N‐H iminophosphoranes with amido complexes (M = Ti, Sm).     

Electrochemical investigation of the chemical diffusion,partial ionic conductivities,and other kinetic parameters in Li3Sb and Li3Bi

The galvanostatic intermittent titration technique (GITT) has been used to electrochemically determine the chemical and component diffusion coefficients, the electrical and general lithium mobilities, the partial lithium ionic conductivity, the parabolic tarnishing rate constant, and the thermodynamic enhancement factor in “Li₃Sb” and “Li₃Bi” as a function of stoichiometry in the temperature range from 360 to 600°C. LiCl, KCl eutectic mixtures were used as molten salt electrolytes and Al, “LiAl” two-phase mixtures as solid reference and counterelectrodes. The stoichiometric range of the antimony compound is rather small, 7 × 10^?3 at 360°C, whereas the bismuth compound has a range of 0.22 (380°C), mostly on the lithium deficit side of the ideal composition. The thermodynamic enhancement factor in “Li₃Sb” depends strongly on the stoichiometry, and has a peak value of nearly 70 000; for “Li₃Bi” it rises more smoothly to a maximum of 360. The chemical diffusion coefficient for “Li₃Sb” is 2 × 10^?5 cm² sec^?1 at negative deviations from the ideal stoichiometry and increases by about an order of magnitude in the presence of excess lithium at 360°C. The corresponding value for “Li₃Bi” is 10^?4 cm² sec^?1 with high lithium deficit, and increases markedly when approaching ideal stoichiometry. The activation energies are small, 0.1–0.3 eV, depending on the stoichiometry, in both phases. The mobility of lithium in “Li₃Bi” is about 500 times greater than in “Li₃Sb” with a lithium deficit. The ionic conductivity in “Li₃Sb” increases from about 10^?4 Ω^?1 cm^?1 in the vacancy transport region to about 2 × 10^?3 where transport is probably by interstial motion at 360°C. For “Li₃Bi” a practically constant value of nearly 10^?1 Ω^?1 cm^?1 is found at 380°C. The parabolic tarnishing rate constant shows a sharp increase at higher lithium activities in “Li₃Sb” whereas in “Li₃Bi” it has a roughly linear dependence upon the logarithm of the lithium activity. The tarnishing process is about 2 orders of magnitude slower for “Li₃Sb” than for “Li₃Bi.” Because of the fast ionic transport in these mixed conducting materials, “Li₃Sb” and “Li₃Bi” may be called “fast electrodes.”     

Differences and Commonalities in the Gas‐Phase Reactions of Closed‐Shell Metal Dioxide Clusters [MO2]+ (M=V,Nb, and Ta) with Methane

High‐level electronic structure calculations, in combination with Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometric studies, permit the mechanism by which closed‐shell, “naked” [TaO₂]⁺ brings about C?H bond activation of methane to be revealed. These studies also help to understand why the lighter congeners of [MO₂]⁺ (M=V, Nb) are unreactive under ambient conditions.     

Redox reactions with bis(η-arene) derivatives of early transition metals

The reactivity of M(η⁶-arene)₂ derivatives of early transition metals (M = Ti, Cr, Mo, arene = MeC₆H₅; M = V, Nb, arene = 1,3,5-Me₃C₆H₃) has been investigated and the syntheses of new and known compounds are described. The derivatives M(CH₃COO)₃, M = Ti, V, Nb, Cr; M(CF₃COO)₃, M = Ti, Nb, Cr; M(acac)₃, M = Ti, V, Mo, acac = acetylacetonato, and M(F₆acac)₃, F₆acac = hexafluoroacetylacetonato, M = V, Nb have been prepared by reaction of the metal bis(arene) derivatives with the appropriate Lewis acid. The crystal and molecular structure of V(F₆acac)₃ has been determined. Hydrogen halides or halogens react with M(η⁶-arene)₂ with formation of metal halides, a highly reactive form of VCl₃ being obtained from V(η⁶-1,3,5-Me₃C₆H₃)₂ and hydrogen chloride in heptane. TiCl₄ oxidizes Ti(η⁶-arene)₂ with complete loss of the arene ligands. An electron transfer process affording ionic derivatives of formula [M(η⁶-MeC₆H₅)₂][TiCl₄(THF)₂], M = Cr (structurally characterized), Mo, has been observed between the THF-adduct of TiCl₄ and the appropriate metal-arene derivative of Group 6.     

Ionization gauge sensitivities of N2, O2, N2O,NO, NO2, NH3, CClF3 and CH3OH

A Bayard-Alpert (BA) gauge was used to determine apparent relative sensitivites S_rel,X for O₂, N₂O, NO, NO₂, NH₃, CClF₃ and CH₃OH from gauge calibration measurements in the range 1.3×10^?1 Pa≤p≤1.3·10^?3Pa. Nitrogen was used as a calibration standard.     

Alloying in an Intercalation Host: Metal Titanium Niobates as Anodes for Rechargeable Alkali‐Ion Batteries

We discuss here a unique flexible non‐carbonaceous layered host, namely, metal titanium niobates (M‐Ti‐niobate, M: Al³⁺, Pb²⁺, Sb³⁺, Ba²⁺, Mg²⁺), which can synergistically store both lithium ions and sodium ions via a simultaneous intercalation and alloying mechanisms. M‐Ti‐niobate is formed by ion exchange of the K⁺ ions, which are specifically located inside galleries between the layers formed by edge and corner sharing TiO₆ and NbO₆ octahedral units in the sol‐gel synthesized potassium titanium niobate (KTiNbO₅). Drastic volume changes (approximately 300–400 %) typically associated with an alloying mechanism of storage are completely tackled chemically by the unique chemical composition and structure of the M‐Ti‐niobates. The free space between the adjustable Ti/Nb octahedral layers easily accommodates the volume changes. Due to the presence of an optimum amount of multivalent alloying metal ions (50–75 % of total K⁺) in the M‐Ti‐niobate, an efficient alloying reaction takes place directly with ions and completely eliminates any form of mechanical degradation of the electroactive particles. The M‐Ti‐niobate can be cycled over a wide voltage range (as low as 0.01 V) and displays remarkably stable Li⁺ and Na⁺ ion cyclability (>2 Li⁺/Na⁺ per formula unit) for widely varying current densities over few hundreds to thousands of successive cycles. The simultaneous intercalation and alloying storage mechanisms is also studied within the density functional theory (DFT) framework. DFT expectedly shows a very small variation in the volume of Al‐titanium niobate following lithium alloying. Moreover, the theoretical investigations also conclusively support the occurrence of the alloying process of Li ions with the Al ions along with the intercalation process during discharge. The M‐Ti‐niobates studied here demonstrate a paradigm shift in chemical design of electrodes and will pave the way for the development of a multitude of improved electrodes for different battery chemistries.     

From the {FeIII2Ln2} Butterfly's Perspective: the Magnetic Benefits and Challenges of Cooperativity within 3 d–4 f Based Coordination Clusters

In this Review we discuss the tuning handles which can be used to steer the magnetic properties of Fe^III-4 f “butterfly” compounds. The majority of presented compounds were produced in the context of project A3 “Di- to tetranuclear compounds incorporating highly anisotropic paramagnetic metal ions” within the SFB/TRR88 “3MET”. These contain {Fe^III₂Ln₂} cores encapsulated in ligand shells which are easy to tune in a “test-bed” system. We identify the following advantages and variables in such systems: (i) the complexes are structurally simple usually with one crystallographically independent Fe^III and Ln^III, respectively. This simplifies theory and anaylsis; (ii) choosing Fe allows ⁵⁷Fe Mössbauer spectroscopy to be used as an additional technique which can give information about oxidation levels and spin states, local moments at the iron nuclei and spin-relaxation and, more importantly, about the anisotropy not only of the studied isotope, but also of elements interacting with this isotope; (iii) isostructural analogues with all the available (i. e. not Pm) 4 f ions can be synthesised, enabling a systematic survey of the influence of the 4 f ion on the electronic structure; (iv) this cluster type is obtained by reacting [Fe^III₃O(O₂CR)₆(L)₃](X) (X=anion, L=solvent such as H₂O, py) with an ethanolamine-based ligand L′ and lanthanide salts. This allows to study analogues of [Fe^III₂Ln₂(μ₃-OH)₂(L′)₂(O₂CR)₆] using the appropriate iron trinuclear starting materials. (v) the organic main ligand can be readily functionalised, facilitating a systematic investigation of the effect of organic substituents on the ligands on the magnetic properties of the complexes. We describe and discuss 34 {M^III₂Ln₂} (M=Fe or in one case Al) butterfly compounds which have been reported up to 2020. The analysis of these gives perspectives for designing new SMM systems with specific electronic and magnetic signatures     

The influence of substituting metals (Ti, V, Cr, Mn, Co and Ni) on the thermal stability of magnetite

In this paper, a systematic study on the influence of substituting metals on the thermal stability of magnetite was carried out. Six series of substituted magnetite (Fe_3?x M _x O₄, M = Ti, V, Cr, Mn, Co and Ni) and Ti–V co-doped magnetite were prepared by a precipitation-oxidation method, followed by the characterization of X-ray diffraction (XRD), X-ray absorption near-edge structure (XANES) spectroscopy and thermogravimetry and differential scanning calorimetry (TG-DSC) analyses. XRD patterns confirmed the formation of samples with spinel structure and XANES probed the valence and site occupancy of the substituting ions. From the TG-DSC analysis results, the substitution of Ti⁴⁺, Mn²⁺, Co²⁺ and Ni²⁺ stabilizes the magnetite structure, while V³⁺ and Cr³⁺ do not show such an effect. For the thermal stability of maghemite, V³⁺ has a negative effect while the other studied ions show a positive effect. In Ti–V co-doped magnetites, the influence of Ti⁴⁺ and V³⁺ on the thermal stability of magnetite is similar to the case of their single-metal-substituted magnetites. The mechanism about the thermal stability change of magnetite by metal substitution was also discussed. The obtained results will be of high importance for the industrial applications of magnetite.     

Über die bei hohen Ansäuerungsgraden auftretenden Polymolybdat-Typen,insbesondere zur Frage der „Dekamolybdate”︁ und „Phase C”︁-Polymolybdate

On the Polymolybdate Types Occurring at High Degrees of Acidification, with Particular Reference to the “Decamolybdates” and “Phase C” Polymolybdates It is shown that in the range of high acidification (> 1.6H⁺/MoO₄^2?) of aqueous molybdate solutions only two types of solid polymolybdates occur, namely the 36-molybdate and the “decamolybdate” types. These types can be most conveniently identified by their Raman spectra and also by some other characteristics. All the other polymolybdate types proposed in the literature for this range of acidification (“hexamolybdates”, “octamolybdates”, “dodecamolybdates”, “16-molybdates”, a 19-molybdate, the large group of polymolybdates characterized by a wide range of b in the general formula M₂O · bMoO₃ · cH₂O, “phase C” polymolybdates, a “hexagonal hydrate of molybdenum trioxide”, a “reactive molybdic acid”, “NH₃(MoO₃)₃”, and others) can be assigned to one of these two types. The most important reason for the erroneous assignments in the literature is the isomorphous exchange of varying quantities of the alkali or alkaline earth metal cations by H₃O⁺ in the crystal structure, occurring in the highly acidic solutions, particularly with the small cations. This cannot be recognized by the presently available methods of investigation and, hence, leads to the creation of new polymolybdate types. Another reason causing some of the confusion is the assignment of virtually identical X-ray diffraction data to two different types of lattices, a hexagonal and cubic lattice.     

Analysis on the local structures for 3d1 impurities (Ti3+ and V4+) in KTiPO4

Making use of the perturbation formulae for 3d¹ ions (Ti³⁺ and V⁴⁺) under orthorhombically compressed octahedra, the spin Hamiltonian parameters (g factors: g_x, g_y, g_z and hyperfine structure constants: A_x, A_y, A_z) and local structures of the 3d¹ impurity centres C₁, C₂, and C₃ in KTiOPO₄ crystals are theoretically analyzed in a consistent way. The remarkable local distortions (i.e., the relative axial compression ratios 11.2%, 7.0%, and 5.5% along Z axis and the relative planar bond length variation ratios 15.9%, 7.0%, and 6.0%) are obtained for the [Ti2O₆]⁹⁻ cluster on Ti2 site and [VO₆]⁸⁻ clusters on Ti1 and Ti2 sites, respectively, in view of the Jahn–Teller effect. The above local orthorhombic distortion parameters in the impurity centres are found to be more significant than the host Ti1 and Ti2 sites in pure KTiOPO₄. The sequences (C₁ > C₂ > C₃) of the local orthorhombic distortion parameters ρ and τ are in accordance with those of the axial and perpendicular anisotropies Δg and δg of g factors, respectively.     

Komplexe in TiCl3-Alkohol-Lösungen

Complexes in TiCl₃-Alcohol Solutions. Whereas in aqueous solution there exist both [Ti · aq₆]³⁺ and [Ti · aq₄Cl₂]¹⁺ ions, in methanol and ethanol only [Ti(ROH)₆]³⁺ ions and in isopropanol only [Ti(ROH)₄Cl₂]¹⁺ ions are present. A crystalline [Ti(MeOH)₆]Cl₃ complex has been prepared.     

Die Kristallstruktur von U2Cr3Si,U4Mn5Si3 und U2Co3Si

Zusammenfassung In den Dreistoffen: Uran–T (Ti,V,Cr,Mn,Co,Nb,W)–{Si,Al} werden Legierungen auf dem Schnitt U(T,Si)₂ bzw. U(T,Al)₂ aus den Komponenten hergestellt und röntgenographisch identifiziert^*. Es bestehen die ternären Verbindungen U₂Cr₃Si, U₄Mn₅Si₃ und U₂Co₃Si, die sich als mit MgZn₂ isotyp erweisen.     

Stereocontrol in Dinuclear Triple Lithium‐Bridged Titanium(IV) Complexes: Solving Some Stereochemical Mysteries

Compounds 1 a – f ‐H₂ form “monomeric” triscatecholate titanium(IV) complexes [Ti( 1 a – f )₃]^2?, which in the presence of Li cations are in equilibrium with the triple lithium‐bridged “dimers” [Li₃(Ti( 1 a – f )₃)₂]^?. The equilibrium strongly depends on the donor ability of the solvent. Usually, in solvents with high donor ability, the stereochemically labile monomer is preferred, whereas in nondonor solvents, the dimer is the major species. In the latter, the stereochemistry at the complex units is “locked”. The configuration at the titanium(IV) triscatecholates is influenced by addition of chiral ammonium countercations. In this case, the induced stereochemical information at the monomer is transferred to the dimer. Alternatively, the configuration at the metal complexes can be controlled by enantiomerically pure ester side chains. Due to the different orientation of the ester groups in the monomer or dimer, opposite configurations of the triscatecholates were observed by circular dichroism (CD) spectroscopy for [Ti( 1 c – e )₃]^2? or [Li₃(Ti( 1 c – e )₃)₂]^?. A surprising exception was found for the dimer [Li₃(Ti( 1 f )₃)₂]^?. Herein, the dimer is the dominating species in weak donor (methanol), as well as strong donor (DMSO), solvents. This is due to the bulkiness of the ester substituent destabilizing the monomer. Due to the size of the substituent in [Li₃(Ti( 1 f )₃)₂]^? the esters have to adopt an unusual conformation in the dimer resulting in a stereocontrol of the small methyl group. Following this, opposite stereocontrol mechanisms were observed for the central metal‐complex units of [Li₃(Ti( 1 c – e )₃)₂]^? or [Li₃(Ti( 1 f )₃)₂]^?.     

Magnesiumiodatdecahydrat Mg(IO3)2 · 10 H2O – Kristallstruktur,Ramanspektren, thermischer Abbau,lone-pair-Radius von Iod(V)

Magnesium Iodate Decahydrate Mg(IO₃)₂ · 10 H₂O – Crystal Structure, Raman Spectra, Thermal Decomposition, Lone-Pair Radius of Iodine(V) Mg(IO₃)₂ · 10 H₂O crystallizes in the triclinic space group P1 (a = 654.25(9), b = 1109.8(2), c = 1176.7(2) pm; α = 105.470(8), β = 104.086(8), γ = 101.744(8)°; Z = 2). The structure has been determined by single-crystal X-ray diffraction at 273 K, and refined to a final R value of 0.0272 for 4372 observed reflections (I > 2σ(I)). The magnesium ions are coordinated to six different H₂O molecules forming a slightly distorted octahedron with Mg? O distances varying between 202.2(2) and 211.6(3) pm. The hexaaquamagnesium ions are arranged parallel to (010). The two kinds of iodate ions and the four different “free” water molecules are filled between the layers thus formed. There are twenty independent hydrogen bonds with O … O distances from 268.7(3) to 287.6(4) pm. On the basis of all intermolecular I … I distances of iodates reported in the literature, 180 pm are recommended as van-der-Waals radius resp. lonepair radius of iodine(V). DSC and Raman spectroscopic experiments as well as high-temperature Raman and X-ray measurements were performed and are discussed with respect to the energetic and geometric distortion of the IO₃^? ions and the dehydration of the decahydrate via the tetrahydrate (308 K) to Mg(IO₃)₂ (428 K).     

Ternäre Lithium-Selten-Erd-Nitrate mit einsamen Nitrationen: Li3[M(NO3)5](NO3) (M = Gd?Lu,Y). Die Kristallstruktur von Li3Er(NO3)6

Ternary Lithium Rare Earth Nitrates with Lonesome Nitrate Ions: Li₃[M(NO₃)₅](NO₃) (M = Gd? Lu, Y). The Crystal Structure of Li₃Er(NO₃)₆ Single crystals of the ternary nitrate Li₃Er(NO₃)₆ are obtained from a solution of “Er(NO₃)₃” in the melt of LiNO₃. In Li₃Er(NO₃)₆ (monoclinic, P2₁/n, Z = 4; a = 776.0(1); b = 748.86(8); c = 2 396(1) pm; β = 90.76(3)°; R1 = 0.0490; wR2 = 0.0792), Er³⁺ is surrounded by five bidentate nitrate ligands yielding the anionic units [Er(NO₃)₅]^2?. These are arranged in the direction of the 2₁ screw axis. Two lonesome NO₃^? ions are in the middle of such a “helix” and are connected by Li⁺ with the anions [Er(NO₃)₅]^2?. The helices are moved against each other by about half of the lattice constant a and are connected by further Li⁺ ions.     

“Complex” versus “free radical” mechanism for the catalytic decomposition of H2O2 by ferric ions

Kinetic and spectrophotometric measurements made during the Fe³⁺ ion catalyzed decomposition of H₂O₂ have been analyzed using the computer simulation method. Improved values of the rate constants of the “complex scheme” and of the molar absorptivities ofthe intermediates were obtained: k₃/K_M = 4.94 M^?1 min^?1, k₄ = 193 M^?1 min^?1, ε_I/K_M = 52.3 M^?2 cm^?1, ε_II = 25.7 M^?1 cm^?1. The simulation revealed details of the reaction which were unavailable by other means and which explained several features of its kinetics. The total amount of O₂ evolved in the reaction using [H₂O₂] ～ 10^?2 M has been calculated and found to be nearly stoichiometric. O₂ evolution experiments in this region cannot, thus, distinguish between the “complex mechanism” predicting nearly stoichiometric evolution of O₂ and the “free radical mechanism” predicting exactly stoichiometricamounts of O₂. There are discrepancies within the “free radical scheme” with regard to the correct values of the rate constants to fit the reactions of H₂O₂ both with Fe²⁺ and Fe³⁺ ions, as well as other reactions assumed to proceed via free radicals.     

Pb3Fe2F12: A new fluorometallate with a tetrameric structural unit

Pb₃Fe₂F₁₂ grown by hydrothermal synthesis, crystallizes in the triclinic system, space group P1 , with a = 7.403(2) Å, b = 7.621(2) Å, c = 9.890(3) Å, α = 110.45(2)°, β = 107.98(1)°, γ = 95.92(2)°, V = 483.12(4) ų, Z = 2. The structure was solved from single crystal data using 3 913 independent reflections (R = 0.045 and R_w = 0.045). Characteristical of this structure is the presence of isolated tetrameric groups [Fe₄F₂₀]^8? in form of “rings” as previously observed in Ba₃Al₂F₁₂. “Independent” fluorine ions are also located and their cationic coordination is discussed. In contrast to Ba₃Fe₂F₁₂, all the rings are parallel in the structure.     

Isotopenverh?ltnismessung von Mo, V, Ti und Zr sowie deren Konzentrationsbestimmung in W?ssern mit einem Thermionen-Quadrupol-Massenspektrometer

Summary Negative MoO ₃ ^– and positive V⁺, Ti⁺, and Zr⁺ thermal ions are produced in a double-filament ion source to determine the isotope ratios of these elements in a quadrupole mass spectrometer. The average relative standard deviation for all isotope ratio measurements is 0.5%. The ratio Me⁺/MeO⁺ (Me=V, Ti, Zr) is followed dependent on the temperature of the ionization filament. A linear plot is obtained for log (Me⁺/MeO⁺) versus 1/T with increasing Me⁺/MeO⁺ ratios for higher temperatures using a single and a double-filament arrangement. An analytical procedure is developed, which allows the simultaneous measurement of Mo and V, and of Ti and Zr as well from one filament by a stepwise variation of the filament temperatures. Mo, V, Ti, and Zr traces in the ng/g and pg/g level of different water samples could be analysed with isotope dilution mass spectrometry using enriched isotopes of⁹⁷Mo,⁵⁰V,⁴⁷Ti, and⁹¹Zr. The precision lies usually in the range of 1 to 6% and the detection limits are 0.002 ng/g for Mo, 0.02 ng/g for V, 0.05 ng/g for Ti, and 0.01 ng/g for Zr using sample amounts of 250 g.