Zur Struktur der LiMIIMIIIF6-Verbindungen. Neue Verbindungen mit MIII=In und Ti

On the Structure of LiM^IIM^IIIF₆ Compounds. New Compounds with M^III=IN and Ti LiMn^IIInF₆ compounds with M^II = Mg, Mn, Co, Ni, Zn, Cd and Ca crystallize in the Na₂SiF₆ structure. The Ti(III) compound LiMgTiF₆ has trirutile structure, LiMnTiF₆ has Na₂SiF₆ and trirutile structure (H.-T. modification), LiCaTiF₆ and LiCdTiF₆ have Li₂ZrF₆ superstructure. With M^II = Co, Ni and Zn solid solutions trirutile — MF₂(rutile) could be only prepared. The lattice constants of all compounds are reported. For LiMnVF₆ and LiFeGaF₆ too dimorphism Na₂SiF₆ trirutile was observed. In the system LiNiCrF₆ (trirutile) — LiMnCrF₆ (Na₂SiF₆ structure) phase limits of both structures are determined in dependence on the ratio of ionic radii r/r. Magnetic data of the In compounds with M^II = Co and Ni and of the Ti(III) compounds with M^II = Mg, Zn, Mn, just as of α- and β-LiMnVF₆ are also given. The three structures only exist if r reaches from 0.6 to 1.2 Å and r from 0.5 to 0.8 Å. The stability-fields are determined by the ratio of ionic radii r/r_Li, r/r_Li and r/r: trirutile 0.9–1.2, Na₂SiF₆ type 1.2–～1.4 and Li₂ZrF₆ superstructure >1.4. The dependence of rate of ionic radii is explained by the different sharing of MF₆ octahedra.     

CO2‐promoted Water‐medium Ullmann Reaction over a Pd/Phenyl‐SBA‐15 Mesoporous Catalyst

Water‐medium Ullmann reaction was carried out in CO₂ atmosphere over the mesoporous Pd/Ph‐SBA‐15 catalyst exhibiting high activity and selectivity owing to the uniform dispersion of Pd particles and hydrophobilic mesoporous channels which facilitate the diffusion and adsorption of organic molecules, especially in an aqueous medium. The CO₂ also shows promoting effect on activity and selectivity, which could be understood by considering the role of H⁺ in the mechanism of Ullmann reaction. The optimum Ph‐Ph yield (84.0%) was obtained at p=0.8 MPa and V=6.0 mL and could remain almost unchanged even after the catalyst has been used repetitively for 5 times.     

The kinetics of the reaction F + H2 → HF + H. A critical review of literature data

Published experimental studies concerning the determination of rate constants for the reaction F + H₂ → HF + H are reviewed critically and conclusions are presented as to the most accurate results available. Based on these results, the recommended Arrhenius expression for the temperature range 190–376 K is k = (1.1 ± 0.1) × 10⁻¹⁰ exp |-(450 ± 50)/T| cm³ molecule⁻¹ s⁻¹, and the recommended value for the rate constant at 298 K is k = (2.43 ± 0.15) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. The recommended Arrhenius expression for the reaction F + D₂ → DF + D, for the same temperature range, based on the recommended expression for k and accurate results for the kinetic isotope effect k/k is k = (1.06 ± 0.12) × 10^×10 exp |-(635 ± 55)/T|cm³ molecule⁻¹ s⁻¹, and the recommended value for 298 K is k = (1.25 ± 0.10) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 67–71, 1997.     

Theoretical Studies on the Structures,Stabilities,Vibrational Spectra,and Thermodynamic Properties of Polyn itromethylbenzenes

The nitro derivatives of methylbenzenes were optimized to obtain their molecular geometries and electronic structures at the DFT‐B3LYP/6‐31G* level. The structure parameters, such as the C–NO₂ bond length (L) and the least C–NO₂ bond overlap population (M) were focused to predict their relative stability or sensitivity. Their IR spectra were obtained and assigned by vibrational analysis, which are reliable compared with the experimental results. Based on the frequencies scaled by 0.96 and the principle of statistic thermodynamics, the thermodynamic properties were evaluated, which are linearly related with the number of nitro and methyl groups as well as the temperature, obviously showing good group additivity.     

Chemical actinometry at 147.0 nm

Hexafluoroacetone (HFA) and O₂ were photolyzed at 147.0 nm to investigate their use in chemical actinometry. The products, CO for the former and O₃ in the latter case, were monitored. For accurate comparison, both of these substances were irradiated by a single light source with two identical reaction cells at 180° to each other. The light intensities I were measured under the same integrated as well as instantaneous photon flux based on ? and ?_CO (quantum yield) as 2 and 1, respectively. Optimum conditions for maximum product yield were 5.0 torr HFA pressure and an O₂ flow rate of 200 ml/min at 1 atm pressure for a 20-minute photolysis period. For light intensity variations between 1.09 × 10¹⁴ and 2.10 × 10¹⁵ photons absorbed/sec, the ratio I/I_HFA was found to be unity. Calibration with the commonly used N₂O actinometer for a ? value of 1.41 showed that I/I_HFA and I/I are unity. Both HFA and O₂ are suitable chemical actinometers at 147.0 nm with ?_CO and ? of 1 and 2, respectively. The light intensity determination in the first case involves the measurement of only one product which is noncondensible at 77°K, whereas wet analysis for O₃, the only product, in the second actinometer is necessary. Both of these determinations are quite simple and are preferable over product analysis in N₂O actiometry, wherein N₂ separation from other noncondensibles at 77°K is required.     

Zum thermischen Verhalten der Hydrogensulfate des Magnesiums,Calciums, Strontiums und Bariums

On the Thermal Behaviour of the Hydrogen Sulfates of Magnesium, Calcium, Strontium and Barium The thermal behaviour of the solvent-free crystals of alkaline earth hydrogen sulfates has been investigated. The DTA and TG curves of M^II(HSO₄)₂ indicate a decomposition following the equation Thermal treatment of Mg(HSO₄)₂ in static gas atmosphere yields α-MgSO₄ which is transformed to α-MgSO₄ at higher temperature. Contrary to that in dynamic gas atmosphere direct decomposition to α-MgSO₄ can be observed. T = 356°C, T = 204°C, T = 175°C, T = 156°C. The strong difference between the peak temperatures of Mg(HSO₄)₂ and the other alkaline earth hydrogen sulfates may be explained not only through the higher covalency of the bondings in the Mg compound but, especially, through differences of their structures. Whereas the hydrogen sulfates of Ca, Sr, and Ba contain chains of edge-linked M^IIO₈ polyhedra, in Mg(HSO₄)₂ exist isolated MgO₆ octahedra.     

The complexing of polymetaphosphate anions with calcium cations: A potentiometric (pCa) study

Calcium cation complexing by polymetaphosphate anions was studied by direct potentiometric measurements with a calcium-ion-sensitive electrode. The moderately stable neutral chelate (Ca₂P₄O)_n is formed in (CaP₂O₆)_n solutions according to the equilibria logK₁₂ values for complexing with polyanions of M_av ? 1200 and 2500 (at C = 0.0003_M) were 5.86 and 6.26, respectively; the K₁₂ values then decreased with increasing polyanion concentration and were reduced by addition of equivalent sodium chloride. The very stable chelate anion (CaP₄O)_n is then formed in (Na₂CaP₄O₁₂)_n solutions according to the equilibrium logK₁₄ values for complexing with polyanions of M_av ? 1200 and 2500 (at C = 0.0003_M) were 7.48 and 8.08, respectively; these K₁₄ values also decreased with polyanion concentration. A less stable complex anion (CaP₆O)_n is formed in more concentrated solutions at PO₃/Ca ratios > 6.     

Über die Reaktion von Schwefel mit Aminen und Formaldehyd. Eine neue Methode zur Herstellung von Thioformamiden und Dithiocarbamaten

The reaction of sulfur with primary or secondary amines and formaldehyde has been studied. A simple one step process for the preparation of thioformamides (RR′NCHS; R ? H, R′ ? CH₃, C₂H₅; R ? R′ ? CH₃, C₂H₅; R+R′ ? ? (CH₂), ? (CH₂), ? C₂H₄OC₂H) and the amine salts of N, N-dialkyl-dithiocarbamic acids (R₂NCS₂ · H₂NR₂, R ? CH₃, C₂H₅, C₄H₉; R₂ ? ? (CH₂), ? (CH₂), ? C₂H₄OC₂H) is reported. In addition, the isolation of diethylamidosulfoxylic acid, (C₂H₅)₂NSOH · 1/2 H₂O, the first derivative of a new class of compounds, is described. The physical properties and the ¹H-NMR. spectra of the above mentioned compounds are given.     

Kinetics and mechanisms of substitution reactions with sulfur-containing nucleophiles in aqueous acid solutions. I—rates of reactions of some tetrahalopalladate (II) anions with thiourea and selenourea

The activation energy parameters for the reaction of PdX (X=Cl^?, Br^?) in aqueous halide acid solution with thiourea (tu) and selenourea (seu) have been determined. High rates of reaction parallel low enthalpies and appreciable negative entropy of activation. The rate law in each case simplifies to k_obs=k[L] where L=tu or seu, and only ligand-dependent rate constants are observed at 25°C. The ligand-dependent rate constants for the first identifiable step in the PdCl + X system is (9.1±0.1) × 10³ M^?1 sec^?1 and (4.5±0.1) × 10⁴ M^?1 sec^?1 for X=tu and seu, respectively, while for the PdBr + X system it is (2.0±0.1) × 10⁴ M^?1 sec^?1 and (9.0±0.1) × 10⁴ M^?1 sec^?1 for X=tu and seu, respectively.     

The mechanism of O(3P) atom reaction with ethylene and other simple olefins

Reactions of oxygen atoms with ethylene, propene, and 2-butene were studied at room temperature under discharge flow conditions by resonance fluorescence spectroscopy of O and H atoms at pressures of 0.08 to 12 torr. The measured total rate constants of these reactions are K = (7.8 ± 0.6)·10^?13cm³s^?1,K = (4.3 ± 0.4) ± 10^?12 cm³ s^?1, K = (1.4 ± 0.4) · 10^?11 cm³ s^?1. The branching ratios of H atom elimination channels were measured for reactions of O atoms with ethylene and propene. No H-atom elimination was found for the reaction of O-atoms with 2-butene. A redistribution of reaction O + C₂ channels with pressure was found. A mechanism of the O + C₂ reaction was proposed and the possibility of its application to other olefins is discussed. On the basis of mechanism the pressure dependence of the total rate constant for reaction O + C₂ was predicted and experimentally confirmed in the pressure range 0.08–1.46 torr.     

Generalized statistical gelation theory

Gel points in random polymerizations of the general type Σ_iRA + Σ_jRB in which A-groups react with A- and B-groups, and B-groups react only with A-groups are considered. (The symbols Σ_i and Σ_i signify that the A- and B-bearing reactants RA and RB can be mixtures of monomers of different functionalities, denoted generally as f_ai and f_bj.) The usual case of A-groups reacting only with B-groups is a special case of the present theory. The effects of chemical kinetics, the competitive reaction of A- and B-groups, are separated from the generalized statistical condition for gelation. The former are used to define reaction curves and the latter, gelation curves. Both types of curve are represented as p_a as a function of p_b. For a given polymerization, gelation occurs when the reaction curve and the gelation curve intersect. When A-groups react only with B-groups, the gel points are those for the usual type of Σ_iRA + Σ_jRB polymerization, and, in the limit of A-groups only reacting with A-groups, the gel points are those for Σ_iRA self polymerizations.     

K21–δNa2+δIn39 (δ = 2.8): A Cluster-Replacement Clathrate-II Structure with an Alkali Metal M136-Network

K_21–δNa_2+δIn₃₉ with δ = 2.82 was synthesized (melted at 973 K, annealed at 623 K) from the elements in sealed niobium ampoules. The compound forms prismatic crystals with silver metallic lustre and is unstable in air and moisture. The crystal structure of K_21–δNa_2+δIn₃₉ (orthorhombic; space group Pnma, No. 62; a = 17.844(5) Å, b = 17.192(3) Å, c = 25.078(7) Å; Z = 4; Pearson code oP248; δ = 2.82, obtained from the structure refinement) contains eight empty In icosahedra of two types, A (12 exo-bonds) and B (7 exobonds), and four open In₁₅ clusters (15 exo-bonds). The latter are centered by K atoms and belong to C units, which are defined as [K(Na₂M₃In₁₅)] heteroatomic clusters (M = K + Na). The spatial distribution of the In icosahedra A, B and heteroatomic clusters C is that of the atoms in the cubic Laves phase MgCu₂: MgCu₂ ? [K(Na₂M₃In₁₅)][In]₂. All the In_n clusters are interconnected by exo-bonds forming a covalent three-dimensional framework (d(In? In) = 2.832 to 3.301 Å). The remaining alkali metal atoms build up a three-dimensional M₁₃₆ network of the clathrate-II type with (16 + 8) cages, which envelopes the In icosahedra and [K(Na₂M₃In₁₅)] clusters. This structure can be described as a cluster-replacement derivative of the clathrate-II structure: (H₂S)₁₆(CCl₄)₈ · (H₂O)₁₃₆ ? [In]₁₆[K(M₅In₁₅)]₈M₁₃₆, and is one member of a novel hierarchical structure family, based upon cluster-replacement. The bonding as well as the structural relationships to other phases are discussed.     

Kinetics and mechanism of the oxidation of some carboxylates by a nickel (III) oxime-imine complex

The kinetics of the oxidation of formate, oxalate, and malonate by |Ni^III(L¹)|²⁺ (where HL¹ = 15-amino-3-methyl-4,7,10,13-tetraazapentadec-3-en-2-one oxime) were carried out over the regions pH 3.0–5.75, 2.80–5.50, and 2.50–7.58, respectively, at constant ionic strength and temperature 40°C. All the reactions are overall second-order with first-order on both the oxidant and reductant. A general rate law is given as - d/dt|Ni^III(L¹)²⁺| = k_obs|Ni^III(L¹)²⁺| = (k_d + nk_s |R|)|Ni^III(L¹)²⁺|, where k_d is the auto-decomposition rate constant of the complex, k_s is the electron transfer rate constant, n is the stoichiometric factor, and R is either formate, oxalate, or malonate. The reactivity of all the reacting species of the reductants in solution were evaluated choosing suitable pH regions. The reactivity orders are: k_HCOOH > k; k > k > k, and k > k < k for the oxidation of formate, oxalate, and malonate, respectively, and these trends were explained considering the effect of hydrogen bonded adduct formation and thermodynamic potential. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 225–230, 1997.     

A Rational Approach to Selective Recognition of NH4+ over K+

An ion-selective electrode (ISE) based on receptor 1 is highly selective for binding NH₄⁺ over K⁺ (lg K=−2.6); the three imine nitrogen atoms in 1 are ideally positioned for hydrogen bonding with the tetrahedral NH₄⁺ ion. This selectivity is considerably greater than that found for commercial ISEs based on nonactin (lg K=−1.0).     

Molecular mechanics studies of ketene derivatives and related structures

The MM2 and MM3 force fields have now been parameterized for ketene and its various derivatives. With the addition of the C_sp ? O bond stretching and C?C_sp?O bond bending parameters, calculations were performed on ketene and six substituted ketene compounds. The MM2 results are quite good with only minimal errors in the calculation of C? H bond lengths and H-C-H bond angles. Additionally, C? F bond parameters in MM2 have been re-adjusted to give better results in monofluorinated species, but, unfortunately, resulting in greater error in the polyfluorinated compounds. The results of geometry calculations by MM3 are similar to those obtained by MM2 with the exception of a significant improvement in the geometry of dimethylketene. The MM3 vibrational frequencies calculated in this study are also in good agreement with available experimental and ab initio results with the exception of a few low frequency in-and out-of-plane bending modes. © 1992 by John Wiley & Sons, Inc.     

The formation of highly excited H in the reaction H2+(v) + H2 → H + H

A quasiclassical trajectory surface hopping method has been used to study H(v) + H₂ → H + H for v = 0, 3, 7, 10, 13, and 17 with an emphasis on determining the H internal energy and angular momentum distributions for high v. For v = 13 and 17, significant cross sections are found for producing H at energies above its dissociation energy. An average metastable H lifetime of 11.5 ps for v = 13 and 4.7 ps for v = 17 is found, but there is also a much longer lived component to the lifetime distributions that is more important for v = 13 than for v = 17. Some of the longer lived metastables correspond to high angular momentum orbiting states of H, but other sources of metastability are also present.     

Thermodynamic Studies on the Complexation Reactions of copper(II) Macrocyclic Tetramine Complexes with Monodentate Ligands: I. RAC-5, 7, 7, 12, 14, 14-Hexamethyl-l, 4, 8, 11-Tetraazacyclotetradecane-Copper(II) (Blue) with-Halide Ions

The possibility of a trigonal bipyramidal structure for [Cu(tet b)X]⁺ (blue) (where X=Cl, Br, I) is supported by the observation of two distinct d-d bands, which are assigned as and d, d_xy→d and d_xz, d_yz→d transitions respectively. The stability constants for the formation of [Cu(tet b)X]⁺ (blue) from [Cu(tet b)]^z+ (blue) and X^? were determined by spectrophotometric method at 25°, 35° and 45°C. The corresponding δH° and δS° values were obtained from the variations of the stability constants between 25° and 45°C     

Acyl- und Alkylidenphosphane. XXXIV [1]. Methoxycarbonylphosphane – Verbindungen aus dem Umfeld des Phosphaalkins PC?O?Li(dme)2

Acyl- and Alkylidenephosphanes. XXXIV. Methoxycarbonylphosphanes – Compounds closely related to the Phosphaalkyne P?C? O? Li(dme)₂ Whereas methyl fluoroformate reacts with an equimolar amount of bis(tetrahydrofuran)lithium bis(trimethylsilyl)phosphanide ( 1a )

1 Die Numerierung des betreffenden Lithiumphosphanids wird um das Suffix a erweitert, wenn von einer Röntgenstrukturanalyse her Gehalt an koordinierendem Solvens und Konstitution bekannt sind. Nach Möglichkeit beziehen wir uns dann im Text und in den Gleichungen auf derartige Spezies.

in 1,2-dimethoxyethane to give an inseparable mixture of tris(methoxycarbonyl)- ( 3 ) and tris(trimethylsilyl)phosphane, colourless crystals of lithium bis(methoxycarbonyl)phosphanide-1,2-dimethoxyethane (2/3) ( 4a ) are isolated in 84% yield from an analogous reaction with (1,2-dimethoxyethane- O,O ′)lithium phosphanide ( 2a ) in a molar ratio of 2:3. When, however, this ratio is changed to 1:2 or 1:1, the ³¹ P nmr spectra of those solutions show the formation of the by-product lithium methoxycarbonylphosphanide ( 10 ) or methoxycarbonylphosphane ( 6 ) respectively. The function of phosphanide 10 as an important intermediate in the synthesis of the phosphaalkyne P?C? O? Li(dme) ₂ ( Ia ) [1] is discussed in detail. With trifluoroacetic acid in 1,2-dimethoxyethane the diacylphosphanide 4a is converted via a lithium-hydrogen exchange into bis(methoxycarbonyl)phosphane ( 9 ). Unlike 1,3-diketones and other diacylphosphanes [25], solutions of this compound do not show the presence of an enol tautomer even in very unpolar solvents. Tris(methoxycarbonyl)phosphane ( 3 ) obtained in a pure state from methyl chloroformate and phosphanide 2a , might decarboxylate to give the corresponding bis(methoxycarbonyl)methyl derivative 5 when the reaction mixture is worked up. ³¹P and characteristic ³¹C nmr data of these methoxycarbonylphosphanes and their related lithium phosphanides are compared with each other, the tris(phenoxycarbonyl) ( 7 ) and the bis(methoxycarbonyl)phenyl compound 8 being included. An x-ray structure determination (P1 ; a 715.8(2); b = 899.5(1); c = 1262.7(2)pm; α = 99.93(1)°; β = 96.01(1)°; γ = 104.81(1)° at ?100±3°C; Z = 1 dimer; wR₂ = 0.152) shows lithium bis(methoxycarbonyl)phosphanide-1,2-dimethoxyethane (2/3) ( 4a ) to crystallize as a centrosymmetric neutral complex. Either lithium square pyramidally coordinated is bound to both carbonyl oxygen atoms of an almost planar bis(methoxy-carbonyl)phosphanide {Li? O_av. 197.4; O ‥ O 280.9} as well as of an 1,2-dimethoxyethane ligand (210.3; 261.6) and is brigded by another solvent molecule (204.0 pm). Further characteristic average bond lengths and angles are as follows: P$ \ddot - $C 179.5; C$ \ddot - $O 122.2; C? O 136.5; O? CH₃ 143.2 pm; C$ \ddot - $P$ \ddot - $C 98.8°; P$ \ddot - $C$ \ddot - $O 132.5°; P$ \ddot - $C? O 107.9°.     

An insight into optical and EPR properties of AgCl and AgF complexes through MS–Xα and SCCEH calculations

MS-Xα and SCCEH calculations on the Ag²⁺ complexes AgF and AgCl (displaying an elongated D_4h symmetry) have been carried out for a better understanding of their experimental optical and EPR properties. As salient features, the present work supports that the unpaired electron in AgCl spends a little more time on ligands than on Ag²⁺, in agreement with the previous analysis of EPR and optical data for KCl:Ag²⁺. Furthermore, the five experimental optical transitions observed in that case are reasonably assigned. The first transition (observed at 12,500 cm^?1) is assigned to a jump involving the 5a_1g orbital built mainly (∽70%) from 3p orbitals of axial ligands, a fact that reflects the distinct level scheme for AgCl when compared to that for more ionic complexes. Calculations on AgF and AgF performed as a function of the equatorial Ag²⁺ –F^? distance led to a reasonable understanding of experimental gyromagnetic and superhyperfine tensors displayed by Ag²⁺ in fluorides. The different relative decrease undergone by g‖– go (8%) and g ? – go (28%) on passing from CsCdF₃:Ag²⁺ to RbCdF₃:Ag²⁺ is shown to be consistent with the formation of AgF and AgF complexes, respectively, related to the different substitutional position of Ag²⁺ in such lattices. The decrement of about 8.5% experienced by both g‖ – go and g? – go values on going from CsCdF₃:Ag²⁺ to NaF:Ag²⁺ is pointed out to reflect the different electrostatic potential (exerted by the rest of the lattice upon the complex) seen by AgF embedded in NaCl or perovskite-type lattices. © 1994 John Wiley & Sons, Inc.     

Metal Complexes with Macrocyclic Ligands. Part XLIV Kinetics of the Cu2+ incorporation into a macrocyclic ligand conjugated to proteins: Model studies for the d‘post-labeling’ technique

The kinetics of the Cu²⁺ complexation by macrocycles 1 (4-[(l,4,8,11-tetraazacyclotetradec-1-yl)methyl]-benzoic acid) and 2 (N-propyl-4-[(1,4,8,11-tetraazacyclotetradec-1-yl)methyl]-benzamide) as well as by macrocycle 1 conjugated to bovine serum albumin (bsa) and to ribonuclease A (rnase) were studied by stopped flow techniques. For 1 and 2 , the kinetics were followed in the mM range monitoring the d-d* absorption band of the Cu²⁺ complex. From the pH dependence of k_obs, the rate law is v = [Cu²⁺] (k_LH[LH] + k[LH₂]), where k_LH and k are the bimolecular rate constants for Cu²⁺ with the diprotonated (LH₂) and monoprotonated (LH₁) form of the ligand, respectively. The values are k = 1.7( 1 ) M^?1s^?1 and k_LH = 2.3(1) 10⁵ M^?1s^?1 for 1 , and k, = 0.28(9) M^?1s^?1 and k_LH = 2.0(1) 10⁵ M^?1s^?1 for 2. The kinetics of the Cu²⁺ incorporation into 1,2 and 1 conjugated to bsa and rnase, i.e., 3 and 4 , respectively, were also followed using nitroso-R salt as a metal indicator in the μM range, i.e., under conditions typical for the ‘post-labeling’ technique to give radiolabeled monoclonal antibodies. In these cases, the reaction takes place between the 1:1 complex of Cu²⁺ with nitroso-R-salt and the macrocycle. At pH 6.5, the rates are very similar to each other indicating that the complexation properties of the macrocycle attached to a protein are not very different from those of the free ligand under comparable conditions.