Berechnungen zur Kinetik der Bildung von Chloro-Bromo-Iodo-Osmaten(IV)

Kinetic Calculations for the Formation of Chloro-Bromo-Iodo-Osmates(IV) Rate constants of formation and ligand exchange reactions of mixed hexahaloosmates(IV) of the type [OsCl_xBr_yI_6?x?y]^2?, x + y = 2?5, are computable taking into account the relative cis- (f = 1, f = 1.75, f ≈? 6) and trans-effects (f = 1, f = 6, f ≈? 10³) of the ligands as well as statistic factors. Using this kinetic data concentration-time diagrams are calculated for reactions including several parallel and consecutive steps. They agree well with the experimentally determined distribution of products in the reaction mixtures. For the preparation of particular mixed ligand complexes the best way of synthesis and maximum yield can be precalculated.     

Kinetics and mechanism of acetylacetonate transfer from acetylacetonatomanganese(III) to iron(III) in acetonitrile catalysis and inhibition effects

The reaction between tris(acetylacetonato)magnanese(III) and hexa(N,N-dimethylformamide)iron(III) perchlorate in acetonitrile proceeds in two stages. The first stage corresponds to the reaction of pentacoordinated Fe(DMF) with Mn(acac)₃, and the rate-determining step of the second stage consists mainly in the elimination of a DMF ligand from Fe(DMF) to yield Fe(DMF) which reacts rapidly with the manganese complex. The formation of Fe(DMF) is catalyzed by Mn(acac)₃, this catalytic effect being decreased by manganese products. The rate-determining step for the formation of Fe(acac)₃ is the transfer of the first acetylacetonate to yield Fe(acac)²⁺. The final products of iron depend on the ratio of reactant concentrations. With Mn or Fe in excess, Fe(acac)₃ or Fe(acac)²⁺ are mainly produced.     

Ternäre Komplexe in Lösung IV. Einfluss von 2,2′-Bipyridyl auf Stabilität und Acidität des Cu2+-Adenosin-5′-monophosphat-N(1)-oxid-1:1-Komplexes

The ternary Cu²⁺?2,2′-bipyridyl-adenosine-5′-monophosphate-N(1)-oxide complex was investigated and compared with the binary Cu²⁺-adenosine-5′-monophosphate-N(1)-oxide complex (I) (cf. [2]). In both complexes Cu²⁺ is bound to the o-amino-N-oxide group of adenosine-5′-monophosphate-N(1)-oxide (HL). The stabilities of the complexes monoprotonated at the phosphate group are of the same order: log K = 11,20, and log K = 11,19. The acidity constants for the deprolonation of the phosphate group in these complexes are slightly different (pK = 5,55, and pK = 5,88), but as expected both values are lower than the corresponding value pK = 6,12 of the ligand.     

Electrochemical sensor for superoxide anion radical using polymeric iron porphyrin complexes containing axial 1‐methylimidazole ligand as cytochrome c mimics

A needle‐type electrochemical sensor for the facile detection of superoxide anion radical (O) was devised using an electrodeposited film of a polymeric porphyrin complex attached to a carbon microelectrode which was placed in a stainless steel 18G needle tube as an auxiliary electrode. The sensing element was prepared by means of electropolymerization of bromoiron(III) meso‐ tetra(3‐thienyl)porphyrin in the presence of 1‐methylimidazole in CH₂Cl₂ containing 100 mM tetrabutylammonium perchlorate (TBAP) as a supporting electrolyte, which gave a smooth film of the corresponding polymer. The film was electrochemically active to give a redox response near −0.05 V versus Ag/AgCl due to the iron(II/III) couple. The microsensor was applied to detect O produced by xanthine oxidation catalyzed by xanthine oxidase. The amperometric response for O was monitored at an electrode potential of 0.5 V versus the auxiliary electrode in a 10 mM phosphate buffer. The microsensor displayed a high catalytic activity for the oxidation of O and showed a linear relationship between the current and the O concentration. Axial coordination of an imidazole ligand to the iron porphyrin center enhanced selectivity for O by impeding the undesired coordination of H₂O₂ that resulted from the dismutation of O. Copyright © 2005 John Wiley & Sons, Ltd.     

Molecular Recognition in Anion Coordination Chemistry. Structure,Binding Constants and Receptor-Substrate Complementarity of a Series of Anion Cryptates of a Macrobicyclic Receptor Molecule

The crystal structures of four anion cryptates [X^? ? BT -6H⁺] formed by the protonated macrobicyclic receptor BT -6H⁺ with F^?, Cl^?, Br^? and N have been determined. They provide a homogeneous series of anion coordination patterns with the same ligand. The small F^?-ion is tetracoordinated, while Cl^? and Br^? are bound in an octahedron of H-bonds. The non-complementarity between these spherical anions and the ellipsoïdal cavity of BT -6H⁺ is reflected in ligand distortions. Structural complementarity is achieved for the linear triatomic substrate N, which is bound by two pyramidal arrays of three H-bonds, each interacting with a terminal N-atom of N. The formation constants of the complexes formed by BT -6H⁺ with a variety of anions (halides, N, NO, carboxylates, SO, HPO, AMP^2?, ADP^3?, ATP^4?, P₂O) have been determined. Very strong complexations are found, as well as marked electrostatic and structural effects on stability and selectivity; in particular the binding of F^?, Cl^?, Br^?, and N may be analyzed in terms of the crystal structure data. The cryptand BT -6H⁺ is a molecular receptor containing an ellipsoïdal recognition site for linear triatomic substrates of size compatible with the size of the molecular cacity. Further developments of various aspects of anion coordination chemistry are considered.     

Hydration structures and energetics of phospholipid

Using previously reported ab initio potentials of the intermolecular interaction energies of phospholipid (PL), Lysophosphatidyl Ethanolamine, with one Na⁺ ion and one water molecule, we performed Monte Carlo simulations for PL-water and PL-Na⁺-water systems. Water-water and PL-water interaction energetics of PL hydration sites are analyzed to understand, in a qualitative way, why the PL head part shows hydrophilicity and the tail part shows hydrophobicity. The interaction of Na⁺ with PL, as well as the interaction of water with PL, is visualized from the analysis of the hydration structures near PL, and the radial distribution functions are analyzed for selected hydration sites. The PL molecule shows much stronger interaction with Na⁺ than with water. The Na⁺ ion is likely to be strongly bound to PO, even to the extent of being trapped, whereas, for water, there exist two strong binding regions near NH and PO. Three water molecules near NH are much more strongly bound than four water molecules near the double-bonded oxygens of PO. The hydrogens of CH₂ adjacent to NH show somewhat strong hydrophilicity, while the hydrogens of CH₂ adjacent to PO does not show such characteristics. The CH₂ groups at the PL tail part give repulsive interactions with water molecules, showing hydrophobicity. Water molecules near the PL tail are stabilized only by water-water interactions.     

Metal Complexes with Macrocyclic Ligands. XI. Ring size effect on the complexation rates with transition metal ions

The 12-16 membered tetraazamacrocycles 1 - 6 were synthesized, their protonation constants and complexation kinetics measured at 25° and I = 0.50. The results of Table 1 Show that pK is strongly influenced by the ring size whereas pK and pK are relatively insensitive to it. This can be understood in terms of electrostatic interactions of the positive charges when located on adjacent amino groups. The kinetics of complex formation between the macrocyclic ligands and several transition metal ions have been studied by pH-stat and stopped-flow techniques and the results have been analyzed as bimolecular reactions between the metal ion and the different protonated species of the ligands. The rate constants, given in Table 2, show that the macrocycles react less rapidly than analogous open chain amines. However, for a given protonated species of the ligand the rate of complexation follows the order Cu²⁺ > Zn²⁺ > Co2⁺ > Ni²⁺ which parallels the sequence of their water exchange rates. For the diprotonated tetraamines LH reacting with Cu²⁺ the slower rates seem to be mainly a consequence of electrostatic interactions, since a correlation between logk and pK exists. For LH⁺, however, the complexation rates of a metal ion with the different macrocycles are all in one order of magnitude and do not depend in a regular way on the ring size or the basicity of the ligand. It is therefore suggested that in this case other factors such as unfavourable preequilibria must be considered as important.     

Assembly of Chiral Two- and Three-dimensional Copper(I) Pseudohalide Based Coordination Polymers with Asymmetrically Substituted Pyrazine and Pyrimidine Ligands

The coordination polymers [(CuCN)₂(μ-2 Mepyz)], [CuCN(μ-2 Mepyz)] and [CuCN(μ-4 Mepym)] ( 1 – 3 ) (2 Mepyz = 2-methylpyrazine; 4 Mepym = 4-methylpyrimidine) may be prepared by self-assembly in acetonitrile solution at 100 °C ( 1 , 3 ) or without solvent at 20 °C ( 2 ). All three contain [CuCN] chains that are bridged by the bidentate aromatic ligands into sheets in 1 and 3 D frameworks in 2 and 3 . Reaction of CuSCN with these heterocyclic diazines at 100 °C leads to formation of the lamellar coordination polymers [(CuSCN)(μ-2 Mepyz)] ( 4 ) and [CuSCN · (4 Mepym-κN1)] ( 5 ), which contain respectively [CuSCN] chains and trans-trans fused [CuSCN] sheets as substructures. The presence of an asymmetric substitution pattern in 2 Mepyz and 4 Mepym induces the adoption of a chiral structure by 2 and 5 (space groups P2₁2₁2₁ and P1).     

Darstellung,Kristallstrukturen und Schwingungsspektren von [OsBr(acac)(PPh3)] und [OsBr(acac)(AsPh3)]

Synthesis, Crystal Structures, and Vibrational Spectra of [OsBr(acac)(PPh₃)] and [OsBr(acac)(AsPh₃)] By reaction of tetrabromoacetylacetonatoosmate(IV) with PPh₃ or AsPh₃ in ethanol the complexes [OsBr(acac)(PPh₃)] ( 1 ) and [OsBr(acac)(AsPh₃)] ( 2 ) are formed, which are purified by chromatography on silica gel. X-ray structure determinations of single crystals of ( 1 ) (monoclinic, space group P 2₁/n, a = 13.035(2), b = 18.2640(14), c = 16.636(3) Å, β = 112.776(14)°, Z = 4) and ( 2 ) (monoclinic, space group P 2₁/c, a = 13.23(5), b = 18.35(2), c = 16.65(2) Å, β = 112.9(5)°, Z = 4) result in mean bond distances Os–P = 2.413, Os–As = 2.483, Os–Br = 2.488 and Os–O = 2.037 Å. The vibrational spectra (10 K) exhibit the inner ligand vibrations of the acac, PPh₃ and AsPh₃ groups with nearly constant frequencies and the stretching vibrations of OsP at 499–522, of OsAs at 330–339, of OsBr at 213–214 and of OsO in the range 460–694 cm^–1.     

Subgroup 4 (Ti,Zr, Hf) derivatives of Cobalt Carbonyls

Bimetallic and trimetallic compounds containing unsupported bonds of subgroup 4 metals (M = Ti, Zr, Hf) and Co were prepared by hydride elimination (A) from RM derivatives (R¹ = PhCH₂; RN; R² = Me, Et)) and by salt elimination (B) from RMX (X = Cl, Br; R.¹ = PhCH₂, RN and R³O; R³= i-Pr, n-Bu)) by reaction with HCo(CO)₄ and Na[Co(CO)₄], respectively. Compounds RMCo(CO)₄ with R¹ = PhCH₂, RM[Co(CO)₄]₂ R.¹ = PhCH₂, were prepared both by methods A and B, while (R³O)₄-n Ti[Co(Co)₄]n (n = 1, 2) compounds were obtained by reaction B. Several tertiary phosphine and phosphite derivatives of the former two types were obtained by substitution of a carbonyl group by PR ligand or by A type reaction of HCo(CO)³(PR with RM compounds.     

Laser ablation of AgSbS2 and cluster analysis by time‐of‐flight mass spectrometry

Thin films of AgSbS₂ are important for phase‐change memory applications. This solid is deposited by various techniques, such as metal organic chemical vapour deposition or laser ablation deposition, and the structure of AgSbS₂(s), as either amorphous or crystalline, is already well characterized. The pulsed laser ablation deposition (PLD) of solid AgSbS₂ is also used as a manufacturing process. However, the processes in plasma have not been well studied. We have studied the laser ablation of synthesized AgSbS₂(s) using a nitrogen laser of 337 nm and the clusters formed in the laser plume were identified. The ablation leads to the formation of various single charged ternary Ag_pSb_qS_r clusters. Negatively charged AgSbS, AgSb₂S, AgSb₂S, AgSb₂S and positively charged ternary AgSbS⁺, AgSb₂S⁺, AgSb₂S, AgSb₂S clusters were identified. The formation of several singly charged Ag⁺, Ag, Ag, Sb, Sb, S ions and binary Ag_pS_r clusters such as AgSb, Ag₃S^?, SbS (r = 1–5), Sb₂S^?, Sb₂S, Sb₃S (r = 1–4) and AgS, SbS⁺, SbS, Sb₂S⁺, Sb₂S, Sb₃S (r = 1–4), AgSb was also observed. The stoichiometry of the clusters was determined via isotopic envelope analysis and computer modeling. The relation of the composition of the clusters to the crystal structure of AgSbS₂ is discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Simple derivation of the potential energy gradient for an arbitrary electronic wave function

The magnitude of reorganization energies in the photoelectron (PE ) spectra of various transition metal compounds with Mn, Fe, and Ni as 3d center is studied by means of a variable INDO Hamiltonian. The Koopmans defects are analyzed as a function of the one-electron resonance integral β and as function of the one- and two-center electron–electron interaction integrals. β has the property of an inverse coupling constant; reorganization effects are enlarged with reduced β values. In the limit of very small resonance integrals a reduction of the calculated Koopmans defects due to modified localization properties of the orbital wave function is encountered. The two-center electron-electron interaction integrals γ have been calculated via an exponential formula with a variable range parameter. In the limit of long-range potentials with flattened γ; gradients a significant reduction of relaxation and correlation is diagnozed; large defects are predicted in the short-range limit with steep gradients in the repulsion potential. The one-center Coulomb and exchange integrals (γ, K) have been modified by a multiplicative factor. With enlarged one-center integrals enhanced Koopmans defects are encountered. The reorganization energies are determined by means of a Green's function approach with a renormalized approximation for the self-energy part.     

Der Jahn-Teller-Effekt des Mn3+-Ions in oktaedrischer Fluorkoordination. Ligandenfeldspektroskopische und magnetische Untersuchungen

Jahn-Teller Effect of Mn³⁺ Ions in Octahedral F^?-Coordination. Ligand Field Spectroscopic and Magnetic Investigations From the ligand field spectra of Mn^IIIF polyhedra in different host lattice structures [AB^IMnF₆ (elpasolite type); B^IIMnF₅; A^IMnF₄ (CsFeF₄ type)] remarkable splittings of the octahedral ⁵E_g groundstate as the consequence of a tetragonal (or lower symmetry) Jahn-Teller component are deduced. The splittings vary between 8500 and 15500 cm^?1 and can be correlated with the extent of Jahn-Teller distortion in the Mn^IIIF polyhedra. While the cooperative Jahn-Teller order is of ferrodistortive symmetry in the elpasolite-structure [exception: (NH₄)₃MnF₆], the tetragonally elongated Mn^IIIF octahedra exhibit an antiferrodistortive order in compounds A^IMnF₄, as was possible to conclude from the magnetic structures found at lower temperatures. The intensities of the sharp, spin-forbidden quintet-triplet transitions in the ligand field spectra vary strongly in dependence on the temperature and the cooperative magnetic order observed for the different classes of compounds.     

Hydration of superoxide studied by molecular dynamics simulation

Molecular dynamics was used to study the hydration of superoxide (O). The Helmholtz free energy of hydration of O was estimated by the thermodynamic integration method. The diffusion of O and the water structure around O were also studied. Two water models were used in the calculations and the results were compared to experiments.     

The role of d orbitals in tetrahedral hybrid orbitals of oxy-ions

The hybrid orbitals of tetrahedral oxy-ions containing some d character have been calculated by maximum overlap method. The d characters of hybrid orbitals increase in the order of SiO, PO, SO, ClO, and decrease in order of GeO, AsO, SeO, BrO. The bond strengths are also obtained for these ions. The hybrid Orbital of VO, CrO, and MnO are of the type d³s as the result of calculation.     

The proton affinity and the structure of protonated species of methylsilane

An ab initio LCAO-MO-SCF calculation was made on the proton affinity (PA ) of methylsilane (CH₃SiH₃) by using STO -3G, MIDI -1, and MIDI -1* basis sets. Three types of protonated methylsilane are taken into account, and their geometrical parameters are optimized. The calculated PA of CH₃SiH₃ is 160.5 kcal/mol, which exceeds that of SiH₄ by 11.5 kcal/mol. The protonated species (I) which refers to Si—C bond protonation is shown to be most favorable, and to be a weak σ-complex between CH₄ and SiH. Other two species are also σ-complexes between H₂ molecule and SiH₃CH or CH₃SiH, and similar to CH, SiH, GeH, and C₂H.     

Darstellung,Kristallstrukturen und Schwingungsspektren von [OsCl(acac)(EPh3)], E = P,As, Sb

Synthesis, Crystal Structures, and Vibrational Spectra of [OsCl(acac)(EPh₃)], E = P, As, Sb By reaction of tetrachloroacetylacetonatoosmate(IV) with PPh₃, AsPh₃ or SbPh₃ in ethanol the complexes [OsCl(acac)(EPh₃)], E = P, As, Sb are formed, which are purified by chromatography on silica gel. X-ray crystal structure determinations of the isotypic single crystals of [OsCl(acac)(EPh₃)] (monoclinic, space group P 2₁/c, Z = 4; E = P ( 1 ): a = 12.972(2), b = 18.255(2), c = 16.517(2) Å, β = 112.61(2)°; E = As ( 2 ): a = 13.173(5), b = 18.299(5), c = 16.429(5) Å, β = 112.346(5)°; E = Sb ( 3 ): a = 13.573(3), b = 18.520(3), c = 16.440(9) Å, β = 111.78(2)°) result in mean bond distances Os–P = 2.412, Os–As = 2.485, Os–Sb = 2.619, Os–Cl = 2.354 and Os–O = 2.032 Å. The IR spectra (10 K) exhibit the inner ligand vibrations of the acac and EPh₃ groups with nearly constant frequencies and the stretching vibrations of OsP at 500–524, of OsAs at 330–339, of OsSb at 271–278, of OsCl at 317–322 and of Os–O in the range 460–694 cm^–1.     

A kinetic study of the autocatalytic permanganate oxidation of formic acid

The kinetics of the permanganate oxidation of formic acid in aqueous perchloric acid has been studied. The results indicate that this reaction is autocatalyzed by both manganese(II) ion (formed as a reaction product) and colloidal manganese dioxide (formed as an intermediate). The apparent rate constants corresponding to the noncatalytic and autocatalytic reaction pathways are given, respectively, by the following equations The activation energies associated with the true rate constants, ??, ??, ??, ??, ??, and ?? are 37.2, 62.5, 70.9, 52.5, 40.8, and 59.9 kJ mol^?1, respectively. The percentage of the total reaction corresponding to each pathway is given for typical experimental conditions. Mechanisms in agreement with the kinetic data are proposed for the six different reaction pathways observed.     

Evaluation of two‐center,three‐ and four‐electron integrals over Slater‐type orbitals in elliptical coordinates

An algorithm for evaluation of two‐center, three‐electron integrals with the correlation factors of the type rr and rrr as well as four‐electron integrals with the correlation factors rrr and rrr in the Slater basis is presented. This problem has been solved here in elliptical coordinates, using the generalized and modified form of the Neumann expansion of the interelectronic distance function r for k ≥ ?1. Some numerical results are also included. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Melt‐state polymer chain dimensions as a function of temperature

The unperturbed chain dimensions (〈R²〉_o/M) of cis/trans‐1,4‐polyisoprene, a near‐atactic poly(methyl methacrylate), and atactic polyolefins were measured as a function of temperature in the melt state via small‐angle neutron scattering (SANS). The polyolefinic materials were derived from polydienes or polystyrene via hydrogenation or deuteration and represent structures not encountered commercially. The parent polymers were prepared via lithium‐based anionic polymerizations in cyclohexane with, in some cases, a polymer microstructure modifier present. The polyolefins retained the near‐monodisperse molecular weight distributions exhibited by the precursor materials. The melt SANS‐based chain dimension data allowed the evaluation of the temperature coefficients [dln 〈R²〉_o/dT(κ)] for these polymers. The evaluated polymers obeyed the packing length (p)‐based expressions of the plateau modulus, G = kT/np³ (MPa), and the entanglement molecular weight, M_e = ρN_anp³ (g mol^?1), where n_t denotes the number (～21) of entanglement strands in a cube with the dimensions of the reptation tube diameter (d_t) and ρ is the chain density. The product np³ is the displaced volume (V_e) of an entanglement that is also expressible as pd or kT/G. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1768–1776, 2002