Polarized neutron study of covalency effects in yttrium iron garnet

Magnetic structure amplitudes of 170 reflections up to sin $\text{θ}\text{λ}\text{= 1.0}\text{A}\text{?}{}^{\mathrm{?1}}$ were measured by polarized neutron diffraction at T = 295K on yttrium iron garnet. The data set was completed by model calculations and the magnetization density was determined. The magnetic moments obtained by integration and refinement are considerably reduced on both iron sites due to charge density transferred from intervening ligand ions. A residual moment of uncancelled spin of (0.032 ±0.004) μ_B is observed on the oxygen ion. Evidence for magnetization density on the oxygen atom and between oxygen and tetrahedral iron was found. A qualitative discussion in terms of a molecular orbital model is given. A further data set collected at 4.2K showed equally a magnetic moment lower than expected for the free ion.     

Break-up stage restoration in multifragmentation reactions

In the case of Xe + Sn at 32MeV/nucleon multifragmentation reaction break-up fragments are built up from the experimentally detected ones using evaluations of light-particle evaporation multiplicities which thus settle fragment internal excitation. Freeze-out characteristics are extracted from experimental kinetic energy spectra under the assumption of full decoupling between fragment formation and energy dissipated in different degrees of freedom. The thermal kinetic energy is determined uniquely while for the freeze-out volume - collective energy a multiple solution is obtained. The coherence between the solutions of the break-up restoration algorithm and the predictions of a multifragmentation model with identical definition of primary fragments is regarded as a way to select the true value. The broad kinetic energy spectrum of ³He is consistent with the break-up genesis of this isotope.     

Structural characterization of the edge double-bridged triruthenium cluster complex Ru3(μ-Cl)2(CO)8(PPh3)2

The title compound is Ru₃(-Cl)₂(CO)₈(PPh₃)2. Crystal data: formula C₄₄H₃₀O₈Cl2P2Ru₃;f _w =1122.9; monoclinic,P2₁; cell parameters (at 293 K)a=10.971(2) Å,b=17.066(2) Å,c=11.833(2) Å,=92.91(1)°,V=2213 ų,Z=2, _calcd=1.68, _meas=1.68. Final discrepancy indices areR(F)=0.030,R _W (F)=0.036. The structure consists of an open trinuclear unit involving two metal-metal bonds [Ru(1)-Ru(2)=2.845(1) Å, Ru(2)-Ru(3)=2.860(1) Å]. The open edge of the metal framework [Ru(1)Ru(3)=3.254(1) Å] is supported by two symmetric bridging chloride ligands [Cl(1)-Ru(1)=2.461(2) Å; Cl(1)-Ru(3)=2.464(2) Å; Cl(2)-Ru(1)=2.470(2) Å; Cl(2)-Ru(3)=2.472(2) Å]. Both phosphorus ligands are cis to the Cl atoms and trans to the unique ruthenium atom Ru(2). Geometric features of the edge dibridged complex are discussed.     

X-ray and neutron diffraction studies of the hydridotriruthenium cluster complex (μ-H)Ru3(CO)7(μ-As(C6H5)CH2As(C6H5)2) ((C6H5 2AsCH2As(C6H5)·CH2Cl2: an example of dibridged metal-metal bond M(μ-H)(μ-X)M,involving a heavy bridgehead atom

The title compound is (μ-H)Ru₃(CO)₇(μ-As(C₆H₅)CH₂As(C₆H₅)₂)((C₆H₅)₂ AsCH₂As(C₆H₅)₂)·CH₂C1₂. Crystal data: monoclinic,P2₁/n, cell parameters (X-ray)a=12.82(2) Å,b=22.91(2) Å,c=17.83(2) Å, β=99.1(3)°; (neutron)a=12.94(1) Å, β=22.95(2)Å,c=17.93(3)Å,β=99.55(5)°. The structure was solved from X-ray data. FinalR indices areR(F)=0.051,R _w (F)=0.049 (X-ray);R(F)=0.064,R _w (F)=0.048,R(F ²)=0.072,R _w (F²)=0.088 (neutron). The complex is derived from Ru₃(CO)₈(dpam)₂ through reaction with hydrogen. The structure consists of a triangular array of metal atoms involving three metal-metal bonds[Ru(1)?Ru(2)=2.912(7)Å;Ru(1)?Ru(3)=2.829(3) A; Ru(2)?Ru(3)=2.845(6) Å]. The metal-metal edge Ru(1)?Ru(2) is supported by a bridging bis(diphenylarsino)methane ligand which lies in the equatorial plane. Activation of the second dpam ligand has generated the new face-bridging ligand unit μ-As(C₆H₅)CH₂As(C₆H₅)₂. In this unit, the bridgehead As atom spans over the Ru(1)?Ru(2) bond, while the second As atom is only bonded to Ru(3). The metal environment is achieved by CO ligands. The hydride ligand is bridging the Ru(1)?Ru(2) vector [Ru(1)?H=1.791(10) Å; Ru(2)?H=1.818(8) Å]. Geometric features of the dibridged Ru(μ-H)(μ-As)Ru bond are discussed.     

Mean potential phase space theory of chemical reactions

A nonconventional application of phase space theory to the insertion reactions A+H(2), with A=C((1)D) and S((1)D), is presented. Instead of approximating the potential energies of interaction between separated fragments by their isotropic long-range contributions, as in the original theory, the latter are replaced by the accurate potential energies averaged with respect to Jacobi angles. The integral and differential cross sections obtained from this mean potential phase space theory (MPPST) turn out to be in very satisfying agreement with the benchmark predictions of the time-independent and time-dependent statistical quantum methods. The formal and numerical simplicity of MPPST with respect to any approach combining statistical assumptions and dynamical calculations makes it a promising tool for studying indirect polyatomic reactions.     

Convenient method to access new 4,4-dialkoxy- and 4,4-diaryloxy-diaza-s-indacene dyes: Synthesis and spectroscopic evaluation

A straightforward method for the synthesis of original 4,4-dialkoxy- or 4,4-diaryloxy-diaza-s-indacenes (BODIPY) derivatives obtained by treatment of BODIPY 1 with various alcohols in the presence of AlCl3 is described. The novel compounds are characterized by spectroscopic properties similar to those of the parent BODIPY 1, absorption and emission spectra with similar band shapes, high molar absorption coefficients (epsilon lambda max approximately 80,000 M(-1) cm(-1)), and for most of them high fluorescence quantum yields (Phi exp from 0.52 to 0.71). Among all of the new compounds synthesized, the dye 2 h exhibits higher fluorescence quantum yield (0.71) and lifetime (4.09 ns) than compound 1 and a good chemical stability toward conditions compatible with biological cell-based assays.     

Dissociation kinetics of Mn2+ complexes of NOTA and DOTA

The kinetics of transmetallation of [Mn(nota)](-) and [Mn(dota)](2-) was investigated in the presence of Zn(2+) (5-50-fold excess) at variable pH (3.5-5.6) by (1)H relaxometry. The dissociation is much faster for [Mn(nota)](-) than for [Mn(dota)](2-) under both experimental and physiologically relevant conditions (t(?) = 74 h and 1037 h for [Mn(nota)](-) and [Mn(dota)](2-), respectively, at pH 7.4, c(Zn(2+)) = 10(-5) M, 25 °C). The dissociation of the complexes proceeds mainly via spontaneous ([Mn(nota)](-)k(0) = (2.6 ± 0.5) × 10(-6) s(-1); [Mn(dota)](2-)k(0) = (1.8 ± 0.6) × 10(-7) s(-1)) and proton-assisted pathways ([Mn(nota)](-)k(1) = (7.8 ± 0.1) × 10(-1) M(-1) s(-1); [Mn(dota)](2-)k(1) = (4.0 ± 0.6) × 10(-2) M(-1) s(-1), k(2) = (1.6 ± 0.1) × 10(3) M(-2) s(-1)). The observed suppression of the reaction rates with increasing Zn(2+) concentration is explained by the formation of a dinuclear Mn(2+)-L-Zn(2+) complex which is about 20-times more stable for [Mn(dota)](2-) than for [Mn(nota)](-) (K(MnLZn) = 68 and 3.6, respectively), and which dissociates very slowly (k(3)～10(-5) M(-1) s(-1)). These data provide the first experimental proof that not all Mn(2+) complexes are kinetically labile. The absence of coordinated water makes both [Mn(nota)](-) and [Mn(dota)](2-) complexes inefficient for MRI applications. Nevertheless, the higher kinetic inertness of [Mn(dota)](2-) indicates a promising direction in designing ligands for Mn(2+) complexation.     

Tannin fingerprinting in vegetable tanned leather by solid state NMR spectroscopy and comparison with leathers tanned by other processes

Solid state 13C-NMR spectra of pure tannin powders from four different sources--mimosa, quebracho, chestnut and tara--are readily distinguishable from each other, both in pure commercial powder form, and in leather which they have been used to tan. Groups of signals indicative of the source, and type (condensed vs. hydrolyzable) of tannin used in the manufacture are well resolved in the spectra of the finished leathers. These fingerprints are compared with those arising from leathers tanned with other common tanning agents. Paramagnetic chromium (III) tanning causes widespread but selective disappearance of signals from the spectrum of leather collagen, including resonances from acidic aspartyl and glutamyl residues, likely bound to Cr (III) structures. Aluminium (III) and glutaraldehyde tanning both cause considerable leather collagen signal sharpening suggesting some increase in molecular structural ordering. The 2?Al-NMR signal from the former material is consistent with an octahedral coordination by oxygen ligands. Solid state NMR thus provides easily recognisable reagent specific spectral fingerprints of the products of vegetable and some other common tanning processes. Because spectra are related to molecular properties, NMR is potentially a powerful tool in leather process enhancement and quality or provenance assurance.     

Energy measurement and fragment identification using digital signals from partially depleted Si detectors

In this work we devise a new method to study quark-anti-quark interactions beyond simple ladder-exchange that yield massless pions in the chiral limit. The method is based on the requirement to have a representation of the quark-gluon vertex that is explicitly given in terms of quark dressings functions. We outline a general procedure to generate the Bethe-Salpeter kernel for a given vertex representation. Our method allows not only the identification of the mesons' masses but also the extraction of their Bethe-Salpeter wave functions exposing their internal structure. We exemplify our method with vertex models that are of phenomenological interest.