Coordination number

A series of new transparent and magnetic germanoborate glasses in the system (100-x)[60GeO2-25B2O3-10Na2O-4Al2O3-1PbO] -(x) Gd2O3, with x = 0, 1, 2, 5, 10, 15 and 20 mol%, was prepared and studied with respect to their thermal and structural changes in the presence of Gd2O3. Based on Differential Scanning Calorimetre (DSC) analysis, a glass with 5% of Gd2O3 showed a high thermal stability, which progressively decreases for samples with higher content of Gd2O3. By the analysis of Raman and Fourier Transform Infrared (FTIR) spectra, it was possible to identify that by increasing the amount of Gd2O3, a progressive depolymerization of 6-membered Ge [IV] rings is promoted, concomitant with an increase of Ge [IV] tetrahedra units with non-briding oxygens. The structural analysis through the local-sensitive techniques EXAFS (Extended X-ray Absorption Fine Structure) and XANES (X-ray Absorption Near Edge Structure) showed that the short-range structural modification around the elements Ge and Gd 3+ does not change with the addition of Gd2O3 and the presence of germanium four-fold coordination [Ge IV ] and Gd 3+ states, respectively. A simulation of the coordination number (N), the interatomic distance (R) of Ge-O and Gd-O bonds and the Debye-Waller factor was also carried out. The microstructure, after crystallization, of the sample with 15 mol% of Gd2O3 was evaluated using optical and electron microscopes. Finally, the paramagnetic behaviour and ion probe quantification of Gd 3+ ions were obtained based on magnetic susceptibility measurements.

The first and probably the most important step in predicting the tertiary structure of proteins from its primary structure is to predict as many as possible secondary structures in a protein chain. Secondary structure prediction problem has been known for almost a quarter of century. In this paper, new machine learning methods such as LAD, LEM2, and MODLEM have been used for secondary protein structure prediction with the aim to choose the best among them which will be later parallelized in order to handle a huge amount of data sets.

Use of 155 Gd Mössbauer spectroscopy allows a straightforward characterization of heterodinuclear Ln-Ln' complexes (LLnLn'(NO3)3•(H2O)2) with a tripodal ligand L, possessing two different N4O3 and O3O3 coordination sites. Thanks to the isomer shift value, the location of the Gd III ion is confirmed; the Gd atom in the Gd-Ln' series (Ln' = Ce, Nd, Eu) occupies the inner N4O3 site with a eight-coordination (N4O3 + O), but on the other hand the Gd atom in the Ln-Gd series (Ln = Dy, Er, Yb) resides in the outer O3O3 site with a ten-coordination (O3O3 + O2 +O2). The smaller isomer shift values for the former indicate that coordination of the basic nitrogen atoms enhances the 6s orbital population. With the help of 151 Eu Mössbauer spectroscopy, we demonstrate that the Gd-Eu entity is a genuine heterodinuclear complex, in which the Gd III ion is located in the inner site and the Eu III ion in the outer oxygenated site. This result highlights the feasibility of our synthetic process described earlier to introduce in a heterodinuclear complex two consecutive ions of the periodic table. And the slow paramagnetic relaxation observed in the 166 Er Mössbauer spectrum of the Er-Gd complex confirms presence of a magnetic interaction in the genuine Er-Gd complex.

Granular packing structures of cohesive microsized particles with different sizes and size distributions, including monosized, uniform, and Gaussian distribution, are investigated by using two different history dependent contact models with discrete element method (DEM). The simulation is carried out in the framework of liggghts, which is a DEM simulation package extended based on branch of granular package of widely used open-source code LAMMPS. Contact force caused by translation and rotation, frictional and damping forces due to collision with other particles or container boundaries, cohesive force, van der Waals force, and gravity is considered. The radial distribution functions (RDFs), force distributions, porosities, and coordination numbers under cohesive and noncohesive conditions are reported. The results indicate that particle size and size distributions have great influences on the packing density for particle packing under cohesive effect: particles with Gaussian distrib...

Hydrostatic pressure effects up to 907 MPa on absorption spectra of chlorophyll a molecules dissolved in diethyl ether have been studied at ambient temperature both experimentally and theoretically using quantum chemistry methods. The fluorescence spectra are studied only experimentally. The data suggest that coordination interactions between the central Mg atom of the chlorophyll and solvent molecules along with interactions that modify the porphyrin skeleton of the solute are responsible for the observed differences of pressure dependence of the Q y , Q x , and Soret spectral bands. The coordination number of the Mg atom changes from five to six between 400 and 600 MPa.

We consider a general spin-1/2 Ising model with multisite interaction on the Husimi lattice with the coordination number q and derive an analytical expression of correlation functions for stable fixed points of the corresponding recurrence relation. We show that for q=2 our model transforms to the two-state vertex model on the Bethe lattice with q=3 and for the case q=3, with only nearest neighbor interactions, we transform our model to the corresponding model on the Bethe lattice with q=3, using the Yang–Baxter equations.

We present a theoretical study on structural and electronic aspects of K + permeation through the binding sites of the KcsA channel's selectivity filter. Density functional calculations are carried out on models taken from selected snapshots of a molecular dynamics simulation recently reported [FEBS Lett. 477 (2000) 37]. During the translocation process from one binding site to the other, the coordination number of the permeating K + ion turns out to decrease and K + ion polarizes significantly its ligands, backbone carbonyl groups and a water molecule. K + -induced polarization increases significantly at the transition state (TS) between the two binding sites. These findings suggest that polarization effects play a significant role in the microscopic mechanisms regulating potassium permeation.

To examine ion solvation, exchange, and speciation for minority components in molten salts (MS) typically found as corrosion products, we propose a multimodal approach combining extended X-ray absorption fine structure (EXAFS) spectroscopy, optical spectroscopy, ab initio molecular dynamics (AIMD) simulations, and rate theory of ion exchange. Going beyond conventional EXAFS analysis, our method can accurately quantify populations of different coordination states of ions with highly disordered coordination environments via linear combination fitting of the EXAFS spectra of these coordination states computed from AIMD to the experimental EXAFS spectrum. In a case study of dilute Ni(II) dissolved in the ZnCl 2 +KCl melts, our method reveals heterogeneous distributions of coordination states of Ni(II) that are sensitive to variations in temperature and melt composition. These results are fully explained by the difference in the chloride exchange dynamics at varied temperatures and melt compositions. This insight will enable a better understanding and control of ion solubility and transport in MS.

Dissolution of the (104) surface of magnesite (MgCO 3 ) was studied as a function of bulk solution pH over the range 2.0 < pH < 5.0 at 60 °C using atomic force microscopy (AFM) with well-defined hydrodynamics. The experimental data and corresponding solution of the convective-diffusion equation for the system revealed that magnesite dissolution is kinetically inhibited by a factor of 10 2 -10 4 relative to the proton mass transport limit. The dissolution flux was found to vary nonlinearly with the surface concentration of H + , [H + ] y)0 , and that inclusion of the homogeneous chemical kinetics of H + consumption in the system to form carbonic acid was unnecessary. The nonlinear behavior was best represented by a Langmuir isotherm for proton adsorption in which the adsorbed entity consists of a surface complex containing more than one proton. The apparent surface kinetic detachment coefficient, k′ n , for this surface complex was determined to be 5 × 10 -12 mol cm -2 s -1 , but the determination of a particular coordination number, n, of this detachment complex was not possible based on the experimental data. The velocity of dissolving + steps was found to be constant, within error, over the entire experimental pH range, whereas the dissolution flux varied by over an order of magnitude in this same range. The AFM images revealed a dramatic increase in step density associated with a large increase in dissolution flux that was attributed to the protonation of terrace-adsorbed carbonate sites (i.e., adions). We propose that the intrinsic protonation constant, K int , differs for adions, kink, step, and terrace sites based on the AFM observations of surface and step morphology as a function of pH.

resulting large structural models (sets of thousands of atomic coordinates) were subjects of geometrical analyses: distributions of the number of first neighbours, as well as local angular correlations have been calculated. In the cases of molecular liquids investigated (like the case of liquid O 2 ), correlations between orientations of neighbouring molecules have been characterized.

We give a detailed discussion of the recently developed Generalized Dynamical Mean-Field Theory (GDMFT) for a mixture of bosonic and fermionic particles. We show that this method is nonperturbative and exact in infinite dimensions and reliably describes the full range from weak to strong coupling. Like in conventional Dynamical Mean-Field Theory, the small parameter is 1/z, where z is the lattice coordination number. We apply the GDMFT scheme to a mixture of spinless fermions and bosons in an optical lattice. We investigate the possibility of a supersolid phase, focusing on the case of 1/2 filling for the fermions and 3/2 filling for the bosons.

Rare-earth titanates form very fragile liquids that can be made into glasses with useful optical properties. We investigate the atomic structure of 83TiO2-17Nd2O3 glass using pair distribution function (PDF) analysis of X-ray and neutron diffraction with double isotope substitutions for both Ti and Nd. Six total structure factors are analyzed (5 neutron + 1 X-ray) to obtain complementary sensitivities to O and Ti/Nd scattering, and an empirical potential structure refinement (EPSR) provides a structural model consistent with the experimental measurements. Glass density is estimated as 4.72(13) g cm−3, consistent with direct measurements. The EPSR model indicates nearest neighbor interactions for Ti-O at $$\overline{r}_{TiO}$$ r ¯ TiO  = 1.984(11) Å with coordination of $$n_{TiO}$$ n TiO  = 5.72(6) and for Nd-O at $$\overline{r}_{NdO}$$ r ¯ NdO  = 2.598(22) Å with coordination of $$n_{NdO}$$ n NdO  = 7.70(26), in reasonable agreement with neutron first order difference functions for ...

In this work, we have developed a polarizable classical interaction potential to study actinoids(III) in liquid water. This potential has the same analytical form as was recently used for lanthanoid(III) hydration [M. Duvail, P. Vitorge, and R. Spezia, J. Chem. Phys. 130, 104501 (2009)]10.1063/1.3081143. The hydration structure obtained with this potential is in good agreement with the experimentally measured ion-water distances and coordination numbers for the first half of the actinoid series. In particular, the almost linearly decreasing water-ion distance found experimentally is replicated within the calculations, in agreement with the actinoid contraction behavior. We also studied the hydration of the last part of the series, for which no structural experimental data are available, which allows us to provide some predictive insights on these ions. In particular we found that the ion-water distance decreases almost linearly across the series with a smooth decrease of coordinatio...

Ag particle-glass composites produced by ion exchange processes of soda-lime glasses were investigated by EXAFS spectroscopy at the Ag K-edge. The spectra measured at 10 K were used to characterize the structure of nanoparticles as a result of ion exchange. The evolution of Ag K-edge EXAFS oscillations measured by in situ heating at 823 K as a function of time clearly shows an increase of Ag-Ag distance and coordination number caused by annealing. Together with transmission electron microscopy characterization a preferred growth of Ag particles with respect to nucleation has been found that leads to increased particle sizes in deeper glass regions.

Currently, the data mining and machine learning fields are facing new challenges because of the amount of information that is collected and needs processing. Many sophisticated learning approaches cannot simply cope with large and complex domains, because of the unmanageable execution times or the loss of prediction and generality capacities that occurs when the domains become more complex. Therefore, to cope with the volumes of information of the current realworld problems there is a need to push forward the boundaries of sophisticated data mining techniques. This thesis is focused on improving the efficiency of Evolutionary Learning systems in large scale domains. Specifically the objective of this thesis is improving the efficiency of the Bioinforma tic Hierarchical Evolutionary Learning (BioHEL) system, a system designed with the purpose of handling large domains. This is a classifier system that uses an Iterative Rule Learning approach to generate a set of rules one by one using consecutive Genetic Algorithms. This system have shown to be very competitive so far in large and complex domains. In particular, BioHEL has obtained very important results when solving protein structure prediction problems and has won related merits, such as being placed among the best algorithms for this purpose at the Critical Assessment of Techniques for Protein Structure Prediction (CASP) in 2008 and 2010, and winning the bronze medal at the HUMIES Awards for Human-competitive results in 2007. However, there is still a need to analyse this system in a principled way to determine how the current mechanisms work together to solve larger domains and determine the aspects of the system that can be improved towards this aim. To fulfil the objective of this thesis, the work is divided in two parts. In the first part of the thesis exhaustive experimentation was carried out to determine ways in which the system could be improved. From this exhaustive analysis three main weaknesses are pointed out: a) the problem-dependancy of parameters in BioHEL's fitness function, which results in having a system difficult to set up and which requires an extensive preliminary experimentation to determine the adequate values for these parameters; b) the execution time of the learning process, which at the moment does not use any parallelisation techniques and depends on the size of the training sets; and c) the lack of global supervision over the generated solutions which comes from the usage of the Iterative Rule Learning paradigm and produces larger rule sets in which there is no guarantee of minimality or maximal generality. The second part of the thesis is focused on tackling each one of the weaknesses abovementioned to have a system capable of handling larger domains. First a heuristic approach to v set parameters within BioHEL's fitness function is developed. Second a new parallel evaluation process that runs on General Purpose Graphic Processing Units was developed. Finally, post-processing operators to tackle the generality and cardinality of the generated solutions are proposed. By means of these enhancements we managed to improve the BioHEL system to reduce both the learning and the preliminary experimentation time, increase the generality of the final solutions and make the system more accessible for end-users. Moreover, as the techniques discussed in this thesis can be easily extended to other Evolutionary Learning systems we consider them important additions to the research in this field towards tackling large scale domains. vi

In situ X-ray absorption and emission spectroscopies (XAS and XES) are used to provide details regarding the role of the accessibility and extent of redox activity of the Mn ions in determining the oxygen reduction activity of LaMnO 3 and CaMnO 3 , with X-ray absorption near-edge structure (XANES) providing the average oxidation state, extended X-ray absorption fine structure (EXAFS) providing the local coordination environment, and XES providing the population ratios of the Mn 2+ , Mn 3+ , and Mn 4+ sites as a function of the applied potential. For LaMnO 3 , XANES and XES show that Mn 3+ is formed, but Mn 4+ ions are retained, which leads to the 4e -reduction between 0.85 and 0.6 V. At more negative potentials, down to 0.2 V, EXAFS confirms an increase in oxygen vacancies as evidenced by changes in the Mn-O coordination distance and number, while XES shows that the Mn 3+ to Mn 4+ ratio increases. For CaMnO 3 , XANES and XES show the formation of both Mn 3+ and Mn 2+ as the potential is made more negative, with little retention of Mn 4+ at 0.2 V. The EXAFS for CaMnO 3 also indicates the formation of oxygen vacancies, but in contrast to LaMnO 3 , this is accompanied by loss of the perovskite structure leading to structural collapse. The results presented have implications in terms of understanding of both the pseudocapacitive response of Mn oxide electrocatalysts and the processes behind degradation of the activity of the materials.

Ti K-edge XANES spectra have been collected on a series of Ti-bearing silicate glasses with metasilicate and tetrasilicate compositions. The intensity of the preedge feature in these spectra has been found to change with glass composition and varies from 29 to 58% (normalized intensity) suggesting a variation in structural environent around the absorbing atom. The pre-edge peak intensity increases for the alkali titanium tetrasilicate glasses from 35% to 58% in the order Li<Na<K<Rb, Cs whereas for the metasilicate compositions there is a maximum for the K-bearing glass. The pre-edge peak intensity remains constant for the alkaline earth titanium metasilicate glasses, Ca and Sr (34%) but increases slightly for Ba (41%). As the intensity of this feature is inversely correlated with coordination number, a comparison of the pre-edge intensity data for the investigated glasses with those of materials of known coordination number leads us to establish a regression equation and to infer that the average coordination number of Ti in these glasses ranges from 4.8 to 5.8. Large alkali cations appear to stabilize a relatively low average coordination number for Ti in silicate melts. The Ti structural environment results appear also to vary as a function of SiO 2 content within the K20-TiO2-SiO2 system. A number of physical properties of the melts from which these glasses were quenched and of other Ti-bearing silicate melts, have been determined in recent years. Clear evidence of a variable coordination number of Ti, consistent with the interpretation of the present XANES data is available from density measurements. These and other property determinations are compared with the present spectroscopic observations in an attempt to relate structure and properties in these melts which contain a major component with variable coordination number.

Structural parameters of the Sr 2+ and, for the first time, of the Eu 2+ ions in aqueous solution were determined by the XAFS method. For the Sr 2+ , the use of an improved theoretical approach led to a first shell coordination number of 8.0 (3), a Sr-O distance of 2.600 (3) Å and a Debye-Waller factor of σ 2 ) 0.0126 (5) Å 2 . These results were confirmed by an analysis performed with experimental phase and amplitude, extracted from the solid reference compound [Sr(H 2 O) 8 ](OH) 2 . The same theoretical approach was used for the analysis of the Eu 2+ XAFS spectra in aqueous solution. This gives a first coordination shell of Eu 2+ formed by 7.2 (3) water molecules, an Eu-O distance of 2.584 (5) Å, and a high Debye-Waller factor of σ 2 ) 0.0138 ( ) Å 2 . Whereas Eu 3+ occurs as an equilibrium between the [Eu(H 2 O) 8 ] 3+ and the [Eu(H 2 O) 9 ] 3+ ions, Eu 2+ occurs in aqueous solution as an equilibrium between a predominant [Eu(H 2 O) 7 ] 2+ ion and a minor [Eu(H 2 O) 8 ] 2+ species.

From simultaneous X-ray diffraction and EXAFS experiments, structural properties in the Wurtzite phase of ZnO have been measured up to the transition pressure (9 GPa). These results are compared with first-principles calculations and discussed in terms of wurtzite mechanical stability at high pressure.

Mesostructured iron oxyhydroxide (FeO x ) and iron oxyhydroxide-phosphate (FeO x P) composites were organized using dodecylsulfate surfactant as a template. X-ray diffraction studies depicted a lamellar structure of the product. Ion exchange and solvent extraction methods were employed for the removal of the surfactant. Carboxylate ions exchanged lamellar type mesostructured material reorganized to a wormhole-like mesoporous material when heated under N 2 atmosphere. Surfactant was completely removed by carboxylate ions as observed by the Fourier transform infrared spectra. High surface area acetate-exchanged FeO x (230 m 2 g -1 ) was obtained after the surfactant removal from the composite (2.8 m 2 g -1 ). Surface area of acetate-exchanged FeO x P was the highest (240 m 2 g -1 ) after the removal of the surfactant. Local structure of iron species of FeO x was investigated by X-ray absorption fine structure spectroscopy. Further, Fe•••Fe bond appeared at 3.21-3.25 Å with coordination number 2-3, showing a high degree of un-saturation of Fe•••Fe bonds. As compared with bulk iron oxyhydroxide and iron-intercalated montmorillonite, the mesoporous iron materials were highly effective for arsenic removal from low concentrations of aqueous solutions. Furthermore, mesoporous iron materials were stable in aqueous phase.

Statistical fluctuations are observed to profoundly influence the clustering behavior of granular material in a vibrated system consisting of two connected compartments. When the number of particles N is sufficiently large ͑N Ϸ 300 is sufficient͒, the clustering follows the lines of a standard second-order phase transition and a mean-field description works. For smaller N, however, the enhanced influence of statistical fluctuations breaks the mean-field behavior. We quantitatively describe the competition between fluctuations and mean-field behavior ͑as a function of N͒ using a dynamical flux model and molecular dynamics simulations.

Six new lanthanide complexes, [Ln(NO 3 ) 2 (L 1 H 2 )](NO 3 ).xCHCl 3 .yH 2 O fLn ¼ Yb (1), x ¼ 1, y ¼ 2; Nd (3), x ¼ 2, y ¼ 3 and Dy (5), x ¼ 2, y ¼ 2g and [Ln(NO 3 ) 2 (L 2 H 2 )](NO 3 ).xCHCl 3 fLn ¼ Yb (2), x ¼ 1; Nd (4), x ¼ 2 and Dy (6), x ¼ 2g, were prepared by NNNOO-donor pentadentate Schiff base ligands N,N 0 -bis(3-methoxysalicylidene)À2,2 0diaminoethylamine (L 1 H 2 ) and N,N 0 -bis(2-hydroxynaphthalidene)À 2,2 0 -diaminoethylamine (L 2 H 2 ). These synthesized complexes were characterized by elemental analysis, FT-IR, 1 H NMR, UV-vis spectroscopy, and mass spectrometry. The thermal characteristics of complexes were studied by TGA technique. The observation of the fluorescence emission properties of ligands L 1 H 2 and L 2 H 2 and its Ln(III) complexes in DMSO solution at excitation wavelength of 320 nm shows that the ligands favor energy transfers to the emitting energy level of Ln(III) complexes. The computational calculations using density functional theory of ligands and its Yb((III) complexes were performed to obtain optimized molecular geometry, the highest occupied molecular orbital, the lowest unoccupied molecular orbital and other parameters. The Schiff bases, metal salts, and its Ln(III) complexes were screened for their in vitro antibacterial studies against Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, and Salmonella typhi bacterial strains. The results of the antibacterial investigation show that the lanthanide complexes possess more potent bactericide properties than ligands and metal salts.

The structure of Ce 3+ , which is responsible for the low-temperature oxygen storage capacity of ceria, was determined by high-energy-resolution fluorescence detected X-ray absorption spectroscopy at the Ce L 3 and L 1 edges. Well-defined ceria nanoparticles (rods, truncated octahedra, and cubes) were synthesized hydrothermally and promoted by platinum nanoparticles. The electronic structure of Ce 3+ does not depend significantly on the nature of the exposed crystallographic planes of CeO 2 particles; it does, however, differ from the electronic structure of known stable compounds containing Ce 3+ ions, such as CeAlO 3 , Ce(NO 3 ) 3 •6H 2 O, and Ce 2 Zr 2 O 7 . Theoretical simulation of Ce L 1 and L 3 X-ray absorption spectra, quantitative analysis of the oxygen storage capacity, and X-ray diffraction data suggest that Ce 3+ ions form both at the surface and in the near-surface layer. Surface and bulk Ce 3+ ions are characterized by elongated Ce-O distances in the first coordination shell and almost the same Ce-Ce distances in the second coordination shell with respect to Ce 4+ in stoichiometric CeO 2 . Ce 3+ ions on the surface of the nanoparticles surface may have a smaller number of oxygen neighbors (as low as six), while in the near-surface layer they tend to have an 8-fold coordination, thus producing oxygen deficit structures similar to Ce 11 O 20 .

The use of aluminum as an electrode in metal-insulator-semiconductor devices containing lanthanum oxide is impaired by unacceptable leakage current levels. Time of flight secondary ion mass spectroscopy depth profiling shows a significant amount of silicon out-diffusion from the substrate and aluminum in-diffusion towards the oxide. By using titanium nitride as the electrode, the silicon out-diffusion is suppressed, which improves the device performance. This indicates that, despite the larger coordination number of the lanthanum ions in the oxide, aluminum acts as a sink for silicon, thus driving the out-diffusion of silicon.

The intramolecular coordination behaviors of MeOOC(CH 2 ) 2 SnCl 3 and MeOOC(CH 2 ) 2 Sn(C C -Ph) 3 are compared, using multinuclear NMR, including 1 H-119 Sn-HMQC spectroscopy. While MeOOC(CH 2 ) 2 SnCl 3 exhibits intramolecular coordination to tin in solution, through the carbonyl oxygen, unlike CH 3 COO(CH 2 ) 3 SnCl 3 which coordinates through the alkoxy oxygen, no firm evidence could be obtained for the existence of such an interaction in MeOOC(CH 2 ) 2 Sn(C C -Ph) 3 . This is ascribed to the lower electronegativity of an alkynyl group, as compared to a chlorine atom, a result which is, however, in contrast with the fact that hydroxy-functionalized vinylSnPh 3 compounds are known from literature to exhibit such weak intramolecular coordinations.

The complex {[(CH 3 ) 2 Sn] 2 [(CH 3 ) 2 SnO](OCH 3 )(HONZO)-coordination mode leads to one seven-coordinate and two five-coordinate tin centers that are linked by a µ 3 -oxo (ONZO)} ( ) [ONZOH is the oximate residue, o-(-ON=CH-C 6 H 4 -OH), HONZO the corresponding phenolate residue, o-function. The coordination geometries are distorted pentagonal bipyramidal and trigonal bipyramidal, (HON=CH-C 6 H 4 -O-), and ONZO the dibasic species o-(-ON=CH-C 6 H 4 -O-), all derived from salicylaldoxime, o-respectively. The two low-coordinate tin atoms are linked by the alkoxide ion. The corresponding chiral (S)-2-methyl-1-(HON=CH-C 6 H 4 -OH)] reacts with an excess of racemic (d,l)-2-methyl-1-butanol to afford the µ 2 -substitution product 5a butanol reacts analogously to yield 5b. By contrast, reaction of 3 with chiral secondary alcohols (2-butanol or 1-phenyl-1-{[(CH 3 ) 2 Sn] 2 [(CH 3 ) 2 SnO][OCH 2 CH(CH 3 )CH 2 CH 3 ](HONZO)-(ONZO)]}. Crystallographic characterisation of the trinuclear ethanol), in various molar ratios, failed to provide the corresponding µ 2 -alkoxy complex. Instead, pure crystals of microcluster 5a shows the presence of the monobasic HONZO ligand in a tridentate µ 2 -O,N mode and of the {[(CH 3 ) 2 Sn] 2 [(CH 3 ) 2 SnO](OH)(HONZO)(ONZO)} (2a) were isolated. dibasic ONZO ligand in a tridentate O,N,O mode. This

Three different metal ions … …w ere selectively introduced at specific positions of ac luster-like structure with a carefully designed ligand H 6 L. In their Communication on page 960 ff., S. Akine,T . Nabeshima, and T. Matsumoto show that [LNiZn 2 La] 3+ could be quantitatively obtained in astepwise process.Different products were obtained when the metal ions were added in ad ifferent order.H owever,u pon heating to overcome the statistical probability, [LNiZn 2 La] 3+ was almost the only product formed among the 54 possible products.

Starting from microscopic and symmetry considerations, we derive the Hamiltonian describing the exchange interaction between the localized Mn spins and the valence band holes in Ga1-xM nxAs. We find that due to the strong spin-orbit coupling in the valence band, this exchange interaction has a rather complex structure and generates a highly anisotropic effective interaction between the Mn spins. The corresponding ground state has a finite ferromagnetic magnetization but is intrinsically spin-disordered even at zero temperature.

Gold on ceria-zirconia is an active catalyst for the low-temperature water-gas shift reaction (LTS), a key stage of upgrading H2 reformate streams for fuel cells. However, this catalyst rapidly deactivates and the mechanism remains unclear. Using stop-start scanning transmission electron microscopy (STEM) to follow the exact same area of the sample at different stages of the LTS reaction, as well as complementary X-ray photoelectron spectroscopy, we observed the activation and deactivation of the catalyst at various stages. During the heating of the catalyst to reaction temperature, we observed the formation of small Au nanoparticles (1-2 nm) from sub-nm Au species. These nanoparticles then agglomerated further over 48 h on-stream, most rapidly in the first 5 h when the highest rate of deactivation was observed. These findings suggest that the primary deactivation process consists of the loss of active sites through the agglomeration and possible dewetting of Au nanoparticles.

Intermediate phases have been observed in covalent glasses, but ionically bonded network systems have received much less attention in this respect. We have now examined titled glasses in m-DSC, Raman scattering, IR reflectance and Birefringence experiments over wide range of soda concentration, 3 &lt; x &lt; 30%. Thermal experiments reveal a sharp reversibility window (RW) in the 14% &lt; x

The influence of the crystal field on the phase diagrams of the bilayer spin-1 Ising model on the Bethe lattice is studied in terms of the intralayer coupling constants J 1 and J 2 of the two layers and interlayer coupling constant J 3 between the layers for given values of the coordination number q by using the recursion relation scheme. The six distinct ground-state configurations of the model are obtained on the ͑J 2 / J 1 , J 3 / qJ 1 ͒ plane with J 1 Ͼ 0, the ferromagnetic coupling, for given values of the crystal field. Then, the phase diagram of the system is obtained on the ͑kT / J 1 , J 3 / J 1 ͒ plane for given values of the crystal field and ␣ = J 2 / J 1 with q = 4 corresponding to the square lattice in real lattice systems. It was found that the system presents both first-and second-order phase transitions, therefore, tricritical points. The paramagnetic phase was also divided into two phases, P + and P -, by studying the thermal behavior of the quadrupolar moments of the two layers.

Quantitative rock physics analyses were used to determine the lithology and pore fluid of a reservoir in the Niger Delta. Inaccurate prediction of lithology and pore fluid results in the inaccurate determination of other petrophysical properties and parameters such as porosity, permeability, and net pay. This research is to predict lithology and pore fluid using rock physics analysis. However, reservoir zones were also predicted. Density, compressional wave velocity, and shear wave velocity logs were used as input to calculate elastic parameters such as velocity ratio, Poisson's ratio, and bulk modulus. The calculated velocity ratio log was used to differentiate between sand and shale. Poisson's ratio and velocity ratio using Goodway interpretation template were carried out and used to delineate pore fluid content, gas sand, oil sand, and sandstone formation from crossplot analysis.

The effect of ternary addition on the stability of an amorphous binary Ni-P or Co-P has been investigated by studying the kinetics of the crystallization of the amorphous electroless films of NixCoyPl5 alloy with different Cobalt-Nickel ratio using differential scanning calorimetry. The nature of as-deposited and phases formed during annealing are identified using electron microscopy and x-ray diffraction. The kinetics of the phase separation and matrix crystallization reaction are determined by non-isothermal annealing. The activation energy, estimated using Kissinger's method, show a definite trend and tends to peak around equal Cobalt to Nickel ratio.

The interaction between two spherical, rigid inclusions in an infinite, linearly viscous, densifying medium has been studied. The stresses in the vicinity of tihe two spheres are highly anisotropic, with significantly enhanced rates of densification in the gap between these particles. A pairwiseadditive approximation for the densification rate of the composite is presented and compared with the composite-sphere and self-consistent models described by Scherer.

l resolves the distributions of both unactivated CCN and cloud droplets and explicitly treats the warm cloud microphysical processes that affect them. Vertical transport is represented with a turbulent kinetic energy closure scheme [P. G. Duynkerke and A. G. M. Driedonks, ibid. 44, 43 (1987)l. The model uses the radiative transfer scheme of 0 . B. Toon, C. P. McKay, T. P. Ackerman, and K. Santhanam [J. Geophys. Res. 94, 16287 (1 989)l. 10. Similar values were estimated by others to be an average CCN production rate [M. B. Baker and R. J. Charlson, Nature 345, 142 (1 990); D. A. Hegg, Geophys. Res. Lett. 17, 21 65 (1 990)l. The distribution of CCN is specified as log-normal with a (number) mean radius of 0.1 bm and a geometr~c SD of 1.2, similar to surface measurements from the remote, cloud-free Pacific Ocean [A. D. Clarke, N. C. Ahlquist, D. S. Covert, J. Geophys. Res. 92, 41 79 (1987)l. Another potential source of CCN, due to subsidence of air from above the are "Ot suited for studies of Stanford ~;l~vers~ty, Stanford, CA 94305.

The coordination environment of Fe(II) has been examined in seven anhydrous ferrosilicate glasses at 298 K and 1 bar using 57 Fe Mössbauer, Fe K-edge X-ray near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS), UV-Vis-NIR, and magnetic circular dichroism (MCD) spectroscopies. Glasses of the following compositions were synthesized from oxide melts (abbreviation and nonbridging oxygen:tetrahedral cation ratio (NBO/T) in parentheses):

A novel metal-organic framework (MOF), [Zn 2 (tdca) 2 (bppd) 2 ]•2DMF, has been synthesized solvothermally using the ligand thiophene-2,5-dicarboxylic acid (H 2 tdca), coligand N,N′-bis(4-pyridylmethylene)-1,4-benzenediamine (bppd), and Zn(NO 3 ) 2 . Single crystal X-ray crystallography reveals that the titled MOF is a three-dimensional pillared-layered MOF. A layer is constituted by a Zn(tdca) unit, and the layers are stabilized by the long hydrocarbon coligand, bppd, which acts as a pillar. A rectangular pore size of 11.42 × 8.12 Å 2 is found in the framework. The porous framework is found to be an excellent fluorescence sensor for the detection of toxic Cd 2+ ion. The sensor shows high selectivity and sensitivity and a quick response toward Cd 2+ . The synthesized MOF is able to not only detect cadmium ions but also adsorb iodine in the gas phase. The MOF can adsorb ∼66% iodine, verified by thiosulfate-iodine titration and TG analysis. Adsorbed iodine can also be removed easily in acetonitrile as well as in n-hexane, which shows that iodine can be reversibly loaded as well as unloaded into the framework.

A series of phosphinoyldithioformate compounds were synthesized from metathesis reactions of K [R 2 P(O)CS 2 ], and R' n PbCl 4-n and R'HgCl. The compounds isolated were characterized using infrared, UV and multinuclear NMR ( 1 H, 13 C, and 31 P) spectroscopy. Structural diversity of these compounds is revealed through analysis of the infrared and NMR spectroscopy, where variable temperature 31 P NMR spectroscopy data of 6 reveals non-rigid coordination behavior and an equilibrium of aniso bonded S,S 4membered ring, and S,O bonded 5-membered ring bonding modes in [MeHg{S 2 CP(O)(Ph) 2 }], (6e6′). The crystal structure of 6′ shows the mercury atom in a T-shape geometry with S,O-bidentate coordinated ligand although room temperature NMR indicated the coordination to the mercury in 6 is non rigid in solution. Variable temperature 31 P NMR spectroscopy yielded an average value of DG # 6-6 ¼ 45.7 ± 1.7 kJ mol À1 for the temperature range of 190 Ke283 K. The crystal structure of [Ph 2 Pb {S 2 CP(O)(Ph) 2 } 2 (H 2 O)], 1, reveals the lead atom in an unusual seven coordinate geometry with two S,Obidentate coordinated ligands and axial phenyl groups. The seventh ligand is a water molecule bonded to lead forming a pentagonal plane.

Several new polyurethane networks based on hyperbranched polyesters (trade name Boltorn ® ) were synthesized to investigate the influence of the hyperbranched crosslinking agent on molecular dynamics of the linear segments containing urethane groups. For comparison, linear polyurethanes as well as polyurethanes crosslinked with the classical crosslinker trimethylolpropane were prepared. Broadband dielectric spectroscopy, dynamic mechanical analysis, and differential scanning calorimetry yielded consistent results concerning molecular relaxation processes; however dielectric spectroscopy appears to be more sensitive concerning the secondary relaxation processes. In the temperature range up to 150 o C, the molecular relaxations were very similar in all the investigated samples, despite considerable structural differences. The weak influence of the crosslinking on the molecular properties could be explained by the existence of hydrogen bonds forming a physical network, which was very dense in this temperature range in comparison with the chemical crosslinks and therefore dominated the molecular mobility in all the investigated systems. This hypothesis was confirmed by rheological measurements performed at temperatures above 150 o C, when the hydrogen bonds should be thermally destroyed. At these temperatures, the effect of crosslinking was manifested by a strong shift of the flowing point: in the linear polyurethanes, this point occurred at much higher frequencies (and lower temperatures) than in the crosslinked analogues.

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BH4) has been synthesized and shown to contain a triply bridged tetrahydroborate moiety. Multinuclear magnetic resonance data ('H, I'B, and 4sSc) are reported for (C5H5)&(BH4) and for Sc(BH4),; double and tripleresonance experiments have allowed the evaluation of all the coupling constants. It is shown that there is no exchange of ring and borohydride protons in (CsHS)2Sc(BH4) in toluene-d8 at elevated temperature as has been claimed for (C2HS)2Zr(BH4)2. In this light, the proposed exchange process has been reinvestigated for (C5D5)2Zr(BH4)2 with use of 2H NMR. The structures of the known main-group and transition-metal borohydrides are rationalized in terms of a correlation between the number of bridging hydrogens and the number of vacant metal orbitals of suitable energy and symmetry. Finally, the similarities in bonding patterns of chloride, tetrahydroborate, and cyclopentadienide groups are analyzed with use of the concept of isolobalit y. 'H, IlB, and 45Sc NMR spectra were obtained on a Bruker WM250 spectrometer operating at 250, 80.21, and 60.735 MHz, respectively. The 45S~(11B) data were obtained with a Bruker WH90 spectrometer operating in the FT mode at 21.964 MHz; "B decoupling was achieved with a General Radio 1164-A frequency synthesizer, locked to a 5-MHz source from the spectrometer, and an RF Communications Inc. Type 805 amplifier. 2H spectra were also obtained on the WH90 operating at 13.815 MHz. Mass spectrometry was performed on a VG Micromass 7070 spectrometer equipped with a VG 2035 data system; the electron energy was 70 eV and the ion source temperature was 200 OC. Infrared spectra were obtained with a Perkin-Elmer Model 283 spectrometer. (CSHs)2Sc(BH4). Anhydrous scandium trichloride was prepared by heating Sc2O3 (Nucor, Phoenix, AZ) with NH4Cl in a furnace at 200 'C for 6 h. The excess NH4CI was removed by vacuum sublimation at 300 O C 6 Following the method of Manzer,' we heated anhydrous scandium trichloride (1.00 g, 6.61 mmol) and freshly (1) For an excellent, comprehensive review of this topic, see:

The 1,1-ethylboration of dichloro(hexyn-1-yl)silane, Cl 2 Si(H)-C≡C-Bu, affords selectively an alkene which is the first example with dialkylboryl and dichlorosilyl groups in cis-positions at the C=C bond. The analogous reaction of dichloro(trimethylsilylethynyl)silane, Cl 2 (H)Si-C≡C-Si Me 3 , leads to a 4:1 mixture of alkenes, in one of which the boryl and dichlorosilyl groups are in trans-positions. The alkenes were characterized by a consistent set of NMR data.

R 2 O 3 -B 2 O 3 binary glasses (R denotes rare-earth elements or Y) were fabricated in a very wide composition region using a levitation technique. The maximum R 2 O 3 content of light rare-earth compounds reached 63 mol % and decreased with a decrease in the ionic radius of R 3+ . The thermal, optical, vibrational, and structural properties were investigated, particularly for 50R 2 O 3 -50B 2 O 3 glasses. The glass transition temperature increased with a decrease in the ionic radius of R 3+ , while the thermal stability was not affected by the glass composition. The packing density increased with a decrease in the ionic radius of R 3+ due to lanthanoid contraction. Raman scattering and Fourier transform infrared spectra revealed that, in the rare-earth-rich glasses, no conventional threedimensional networks consisting of corner-sharing BO n (n = 3 or 4) units existed because all B atoms were formed as isolated BO 3 units. The simple environment around B atoms in the glasses led to additional IR transmittance regions, irrespective of the kinds of R. The total correlation functions obtained from high-energy X-ray diffraction measurements were analyzed using the pair-function method and compared with those of various RBO 3 crystalline phases. It was suggested that the local structure around R resembles the ν-NdBO 3type crystal structure, and the O coordination number of R ranged from 6.5 to 7.7, smaller than that of the crystalline phase. The glass-forming ability depending on R was discussed based on the structural similarities between the melt, glass, and crystalline phases.