How does basis set superposition error change the potential surfaces for hydrogen-bonded dimers?

We describe a simple method to automate the geometric optimization of molecular orbital calculations of supermolecules on potential surfaces that are corrected for basis set superposition error using the counterpoise (CP) method. This method is applied to the H-bonding complexes HF/HCN, HF/H2O, and HCCH/H2O using the 6-31G(d,p) and D95 + + (d,p) basis sets at both the Hartree-Fock and second-order M��ller-Plesset levels. We report the interaction energies, geometries, and vibrational frequencies of these complexes on the CP-optimized surfaces; and compare them with similar values calculated using traditional methods, including the (more traditional) single point CP correction. Upon optimization on the CP-corrected surface, the interaction energies become more negative (before vibrational corrections) and the H-bonding stretching vibrations decrease in all cases. The extent of the effects vary from extremely small to quite large depending on the complex and the calculational method. The relative magnitudes of the vibrational corrections cannot be predicted from the H-bond stretching frequencies alone

New mono- and dinuclear ruthenium complexes containing the 3,5-bis(2-pyridyl)pyrazole ligand. Synthesis, characterization and applications

Se han sintetizado dos nuevos complejos mononucleares de Ru, con formula [RuCl2(Hbpp)(dmso)2], a partir de la reacci��n entre [RuCl2(dmso)4] y Hbpp (3,5-bis(2-piridil)pirazola). El hecho que s��lo tres de los seis posibles estereois��meros se obtengan a partir de esta reacci��n, se ha racionalizado en base a factores estructurales y electr��nicos. Estos complejos se han caracterizado de forma estructural, espectrosc��pica y electroqu��mica. En acetonitrilo en medio b��sico, el is��mero trans,cis-[RuCl2(Hbpp)(dmso)2] da lugar a procesos de isomerizaci��n de enlace de un ligando dmso cuando el Ru(II) se oxida a Ru(III). Las constantes termodin��micas y cin��ticas para el proceso se han determinado por voltametria c��clica. La irradiaci��n de trans,cis-[RuCl2(Hbpp)(dmso)2] y cis(out),cis-[RuCl2(Hbpp)(dmso)2] con luz UV o solar da lugar a reacciones de fotosustituci��n de un ligando dmso por una mol��cula de acetonitrilo para dar un nuevo compuesto el cual ha sido caracterizado en soluci��n por t��cnicas espectrosc��picas y electroqu��micas. Ambos complejos resultan catalizadores ��tiles en la transferencia de hidr��geno de isopropanol a acetofenona, obteni��ndose 1-feniletanol como ��nico producto y un 42.1% de conversi��n (36.1 ciclos met��licos) a 80��C con el is��mero trans,cis-[RuCl2(Hbpp)(dmso)2], que resulta significativamente m��s eficaz que el complejo cis(out),cis-[RuCl2(Hbpp)(dmso)2]. La reacci��n de cis(out),cis-[RuCl2(Hbpp)(dmso)2] con trpy (2,2':6',2"-terpiridina) da lugar a los dos is��meros geom��tricos del complejo [Ru(Hbpp)(trpy)(Cl)]+, el in y el out. Estos complejos se han aislado y caracterizado por t��cnicas estructurales, espectrosc��picas y electroqu��micas. Estos cloro complejos han sido utilizados como precursores para la s��ntesis de los complejos an��logos con ligandos aqua (in,out-[Ru(Hbpp)(trpy)(H2O)]2+) y piridina (in,out-[Ru(Hbpp)(trpy)(py)]2+), los cuales tambi��n han sido aislados y caracterizados. Las propiedades ��cido-base de los aqua complejos, y del complejo out-py se han estudiado detalladamente por voltametria c��clica y mediante valoraciones espectrofotom��tricas ��cido-base. El tratamiento matem��tico de los datos as�� obtenidos nos ha permitido determinar los valores de pKa para los distintos equilibrios de protonaci��n de los complejos en los estados de oxidaci��n II y III. El complejo out-aqua ha demostrado ser un buen catalizador para la oxidaci��n electroqu��mica del alcohol benz��lico, presumiblemente a benzaldehido. La constante de velocidad de segundo orden para el proceso ha sido determinada como 17.1 M-1 s-1, por simulaci��n matem��tica. El d��mero con un puente cloro, [Ru2Cl(bpp)(trpy)2]2+ ha sido preparado por dos rutas sint��ticas diferentes. El d��mero an��logo con un puente acetato se ha obtenido por reacci��n del cloro d��mero con un exceso de acetato s��dico. El d��mero con dos ligandos aqua [Ru2(bpp)(trpy)2(OH2)2]3+ puede obtenerse por hidr��lisis ��cida del complejo con un acetato puente o por hidr��lisis b��sica del complejo con un puente cloro. Estos complejos han sido caracterizados por t��cnicas estructurales, espectrosc��picas y electroqu��micas. Las soluciones del d��mero con dos ligandos aqua en medio ��cido resultan inestables a la coordinaci��n de aniones de la soluci��n con el tiempo. Las propiedades ��cido-base del d��mero con dos aguas coordinadas han sido estudiadas por voltametria c��clica y mediante experimentos de electr��lisis a potencial controlado. El pKa para la desprotonaci��n de uno de los ligandos aqua ha sido determinado mediante una valoraci��n espectrofotom��trica ��cido-base como 6.7. Este valor tan bajo de pKa se atribuye a la formaci��n de la entidad {Ru2O2H3}, favorable termodin��micamente. Los espectros UV-vis para los distintos estados de oxidaci��n del aqua d��mero, de RuIIRuII a RuIIIRuIV, han sido obtenidos por oxidaci��n qu��mica y electroqu��mica del complejo. Se han llevado a cabo estudios cin��ticos de la oxidaci��n, paso a paso, de RuII,II a RuIV,IV , y se han determinado las constantes de oxidaci��n de segundo orden para los distintos procesos de oxidaci��n. La capacidad del aqua d��mero en la oxidaci��n del agua a ox��geno molecular ha sido investigada en soluci��n homog��nea utilizando CeIV como oxidante. La evoluci��n de ox��geno se ha demostrado por cromatografia de gases. Se ha obtenido una eficiencia del 73% y 18.6 ciclos catal��ticos, cuando 1.83 x 10-6 moles de d��mero se han mezclado con un exceso de 100 equivalentes de cerio. El d��mero con dos aguas cataliza tambi��n la oxidaci��n del agua de forma heterog��nea, con el complejo adsorbido sobre una membrana de nafion, aunque la eficiencia es menor. Se ha propuesto un mecanismo intramolecular para la reacci��n de oxidaci��n del agua. Consiste en la oxidaci��n a 4 electrones del d��mero, de RuII,II a RuIV,IV, el cual reacciona con el agua para formar ox��geno y revierte nuevamente al estado de oxidaci��n II,II. Este modelo es consistente con estudios catal��ticos de la evoluci��n de ox��geno en funci��n de las concentraciones de cerio y catalizador, llevados a cabo en soluci��n ��cida homog��nea, que demuestran que la oxidaci��n a 4 electrones del agua se encuentra catalizada por una sola mol��cula de complejo bajo concentraciones elevadas de cerio. La constante de pseudo-primer-orden para la evoluci��n de ox��geno tiene un valor de 1.4 x 10-2 s-1, que es uno de los valores de constante m��s elevados obtenidos hasta la fecha. Desafortunadamente, el aqua d��mero se desactiva durante el proceso de cat��lisis dando lugar a una especie naranja, la cual estamos actualmente tratando de caracterizar.

New Ruthenium complexes containing N, P and S-donor type of ligands: coordination chemistry, characterization and application to asymetric and non-asymetric catalysis

S��ntesi de nous complexos de Ruteni amb lligands no quirals que tenen per f��rmula [Ru(phen)([9]aneS3)X] (on X = H2O, py i MeCN). Caracteritzaci�� espectrosc��pica electroqu��mica i estructural d'aquesta fam��lia de complexos. Estudi de les seves propietats catal��tiques en front a l'oxidaci�� de substrats org��nics com l'alcohol benz��lic en reaccions d'electrocat��lisi. Avaluaci�� cin��tica dels mecanismes de substituci�� entre els complexos Ru-py i Ru-MeCN. Generaci�� d'un interruptor molecular foto-indu��t. S��ntesi de nous complexos quirals de Ru atropoisom��ricament purs amb lligands oxazol��nics que tenen per f��rmula [Ru(trpy)(Ph-box-R)X] on (X = Cl, H2O, py, MeCN, 2-OH-py). Caracteritzaci�� estructural exhaustiva en estat s��lid (Raig-X) en soluci�� (RMN) i en fase gas (c��lculs DFT). Avaluaci�� de la seva activitat catal��tica en reaccions asimmetriques d'epoxidaci�� de substrats proquirals. S��ntesi de nous lligands polipirid��lics quirals amb simetria C3. Estudi de la seva qu��mica de coordinaci�� i avaluaci�� de la seva activitat catal��tica en reaccions asimmetriques d'oxidaci�� i reducci��.

S��ntesi i Caracteritzaci�� de Nous Complexos de Ruteni contenint Lligands Quirals. Aplicacions en Cat��lisi Asim��trica

La Tesis describe una serie de complejos de Rutenio conteniendo ligandos quirales y su aplicaci��n en cat��lisis asim��trica. Por un lado se describe el complejo [RuCl(bpea)((S)-BINAP)](BF4), donde (S)-BINAP es una difosfina quiral y bpea un ligando N-tridentado. Su aplicaci��n en cat��lisis de hidrogenaci��n asim��trica de sustratos olef��nicos y carbon��licos, tanto en fase homog��nea como heterog��nea (tras inmovilizaci��n sobre soportes alumino-fosfato), ha mostrado excelentes resultados de conversi��n y excesos enantiom��ricos. Aparte, se ha desarrollado una familia de complejos con f��rmula [Ru(T)(B)X], donde T representa un ligando tri-N-dentado, B una di-oxazolina quiral y X es Cl o H2O. Se ha estudiado la actividad catal��tica de los aquocomplejos con T = tpm en epoxidaciones, determin��ndose la influencia de los sustituyentes en B sobre el rendimiento y la quimioselectividad, favorecidos por interacciones de tipo π-stacking. El uso de otros ligandos tridentados ha llevado a su rotura, habi��ndose caracterizado sin embargo los correspondientes complejos

Systematic studies on 3d-3d and 3d-4f multimetallic complexes with interesting magnetic and/or luminescent properties

324 p.

Aqueous geochemistry and oxygen isotope compositions of acid mine drainage from the R��o Tinto, SW Spain, highlight inconsistencies in current models

The Rio Tinto river in SW Spain is a classic example of acid mine drainage and the focus of an increasing amount of research including environmental geochemistry, extremophile microbiology and Mars-analogue studies. Its 5000-year mining legacy has resulted in a wide range of point inputs including spoil heaps and tunnels draining underground workings. The variety of inputs and importance of the river as a research site make it an ideal location for investigating sulphide oxidation mechanisms at the field scale. Mass balance calculations showed that pyrite oxidation accounts for over 93% of the dissolved sulphate derived from sulphide oxidation in the Rio Tinto point inputs. Oxygen isotopes in water and sulphate were analysed from a variety of drainage sources and displayed delta O-18((SO4-H2O)) values from 3.9 to 13.6 parts per thousand, indicating that different oxidation pathways occurred at different sites within the catchment. The most commonly used approach to interpreting field oxygen isotope data applies water and oxygen fractionation factors derived from laboratory experiments. We demonstrate that this approach cannot explain high delta O-18((SO4-H2O)) values in a manner that is consistent with recent models of pyrite and sulphoxyanion oxidation. In the Rio Tinto, high delta O-18((SO4-H2O)) values (11.2-13.6 parts per thousand) occur in concentrated (Fe = 172-829 mM), low pH (0.88-1.4), ferrous iron (68-91% of total Fe) waters and are most simply explained by a mechanism involving a dissolved sulphite intermediate, sulphite-water oxygen equilibrium exchange and finally sulphite oxidation to sulphate with O-2. In contrast, drainage from large waste blocks of acid volcanic tuff with pyritiferous veins also had low pH (1.7). but had a low delta O-18((SO4-H2O)) value of 4.0 parts per thousand and high concentrations of ferric iron (Fe(III) = 185 mM, total Fe = 186 mM), suggesting a pathway where ferric iron is the primary oxidant, water is the primary source of oxygen in the sulphate and where sulphate is released directly from the pyrite surface. However, problems remain with the sulphite-water oxygen exchange model and recommendations are therefore made for future experiments to refine our understanding of oxygen isotopes in pyrite oxidation. (C) 2009 Elsevier B.V. All rights reserved.

Availability of heavy metals for uptake by Salix viminalis on a moderately contaminated dredged sediment disposal site

Extractability of Cd. Cr, Cu, Ni, Pb, and Zn in a dredged sediment disposal site was assessed using single extraction Procedures (H2O; 0.01 M CaCl2; 1 M NH4OAc NH4OAc-EDTA. CaCl2-TEA-DTPA). Only Cd and Zn were Found to exceed statutory threshold values for total content. The field was planted with Salix viminalis "Orm" and accumulation of heavy metals in bark, leaves, roots, and wood was evaluated at seven sampling locations along an observed gradient in texture and pollution. Biomass production was high, ranging from 13.2 to 17.8 t ha(1) y(1) dry weight. Metal accumulation in aboveground Plant parts Was low. amounting to the following annually extracted mass or metals per ha: 5034 g Zn, 83 g Cd. W g Cu. 83 g Pb, 12 g Ni and 6 g Cr. The use of accumulating clones and the use of soil amendments might enhance extraction efficiency in future research. (C) 2005 Elsevier Ltd. All rights reserved.

Factors influencing the dissolution of phosphate rock in a range of high P-fixing soils from Cameroon

A laboratory incubation experiment was conducted to evaluate the soil factors that influence the dissolution of two phosphate rocks (PRs) of different reactivity (Gafsa, GPR, reactive PR; and Togo-Hahotoe, HPR, low reactivity PR) in seven agricultural soils from Cameroon having variable phosphorus (P)- sorption capacities, organic carbon (C) contents, and exchangeable acidities. Ground PR was mixed with the soils at a rate of 500 mg P kg 21 soil and incubated at 30 degrees C for 85 days. Dissolution of the PRs was determined at various intervals using the Delta NaOH-P method ( the difference of the amount of P extracted by 0.5 M NaOH between the PR-treated soils and the control). Between 4 and 27% of HPR and 33 and 50% of GPR were dissolved in the soils. Calcium (Ca) saturation of cation exchange sites and proton supply strongly affected PR dissolution in these soils. Acid soils with pH-(H2O), < 5 (NKL, ODJ, NSM, MTF) dissolved more phosphate rock than those with pH-(H2O) > 5 (DSC, FGT, BAF). However, the lack of a sufficient Ca sink in the former constrained the dissolution of both PRs. The dissolution of GPR in the slightly acidic soils was limited by increase in Ca saturation and that of HPR was constrained by limited supply in protons. Generally, the dissolution of GPR was higher than that of HPR for each soil. The kinetics of dissolution of PR in the soils was best described by the power function equation P At B. More efficient use of PR in these soils can be achieved by raising the soil cation exchange capacity, thereby increasing the Ca sink size. This could be done by amending such soils with organic materials.

The origin of brines underlying Lake Kinneret

Lake Kinneret (LK) is a relatively fresh water take situated in the Dead Sea Rift (DSR) Valley. The pore water (PW) in the sediments underlying LK pelagic zone have significantly higher salinity than that of the lake. The concentrations of major ion solutes (Cl, Br, Na, K, Mg) in PW from six 2.4 m to 5.1 m long sediment cores increase linearly with depth, indicating the occurrence of saline, deep seated brines. The upper part of the PW column is affected by the much fresher boundary with LK water and in most cores is characterized by gradually increasing Br/Cl and decreasing Na, Mg, K/Cl molar ratios, which tend to stabilize at about 2.0 m below the sediment surface. The 'stable' molar ratios in the deeper PW vary spatially and are supposed to represent the ratios in the deep underlying brines at each site. When plotted as Na/Cl vs. Br/Cl, the stable ratios of the northern and central part of the lake fall close to a straight line which characterizes many of the brines in the DSR Valley. However, the respective ratios in the southern part of the lake fall markedly off the DSR line. Moreover, Na/Cl and K/Cl molar ratios in the south are significantly higher than in the central and northern parts. delta Cl-37 measured in present LK water is ca. 0.0 parts per thousand. Along the PW column at the lake center, delta Cl-37 is becoming more positive with depth, reaching values of about +0.5 parts per thousand to +0.6 parts per thousand at 3 m depth. Even more positive values (+0.7 parts per thousand to +0.8 parts per thousand) are detected further north, in PW from deeper sediment layers. In contrast, in PW from the southeastern part of the lake, delta Cl-37 is becoming more negative with depth (-1.0 parts per thousand at similar to 2.6 m). It is suggested that these isotopic differences are also indicative of spatial variability in the PW brine sources. O-18 and D values in the PW of all 3 m long cores are similar and resemble the respective levels in LK. The source of H2O in 3 m deep, bed sediments is claimed to be the overlying lake water, and therefore water isotopes do not provide a clue regarding the original water isotopic composition in the underlying brines. PW from the southeast with higher K/Cl and Na/Cl but lower concentrations of these solutes, suggest leaching by meteoric water of sub-surface halite and post-halite salt formations, while the more saline PW from the northern and central parts, that have lower K/Cl and Na/Cl, and higher Br/Cl, are similar to DSR brines and represent underlying residual brines. (C) 2009 Elsevier B.V. All rights reserved.

Assessment of the consistency of near-infrared water vapor line intensities using high-spectral-resolution ground-based Fourier transform measurements of solar radiation

Calculations of the absorption of solar radiation by atmospheric gases, and water vapor in particular, are dependent on the quality of databases of spectral line parameters. There has been increasing scrutiny of databases such as HITRAN in recent years, but this has mostly been performed on a band-by-band basis. We report nine high-spectral-resolution (0.03 cm(-1)) measurements of the solar radiation reaching the surface in southern England over the wave number range 2000 to 12,500 cm(-1) (0.8 to 5 mm) that allow a unique assessment of the consistency of the spectral line databases over this entire spectral region. The data are assessed in terms of the modeled water vapor column that is required to bring calculations and observations into agreement; for an entirely consistent database, this water vapor column should be constant with frequency. For the HITRAN01 database, the spread in water vapor column is about 11%, with distinct shifts between different spectral regions. The HITRAN04 database is in significantly better agreement (about 5% spread) in the completely updated 3000 to 8000 cm(-1) spectral region, but inconsistencies between individual spectral regions remain: for example, in the 8000 to 9500 cm(-1) spectral region, the results indicate an 18% (+/- 1%) underestimate in line intensities with respect to the 3000 to 8000 cm(-1) region. These measurements also indicate the impact of isotopic fractionation of water vapor in the 2500 to 2900 cm(-1) range, where HDO lines dominate over the lines of the most abundant isotope of H2O.

Hydrolysis of N2O5 on submicron sulfuric acid aerosols

The kinetics of reactive uptake of gaseous N2O5 on submicron sulfuric acid aerosol particles has been investigated using a laminar flow reactor coupled with a differential mobility analyzer (DMA) to characterize the aerosol. The particles were generated by homogeneous nucleation of SO3/H2O mixtures. In the H2SO4 concentration range 26.3���64.5 wt % the uptake coefficient was �� = 0.033 �� 0.004, independent of acid strength. For an acid strength of 45 wt % �� was found to decrease with increasing temperature over the range 263���298 K. From this, temperature dependence values of ���115 �� 30 kJ/mol and ���25.5 �� 8.4 J/K mol were determined for the changes in enthalpy and entropy of the uptake process, respectively. The results are consistent with a previous model of N2O5 hydrolysis involving both a direct and an acid catalyzed mechanism, with uptake under the experimental conditions limited by mass accommodation.

On the relationship of normal modes to local modes in molecular vibrations

A simple model for the effective vibrational hamiltonian of the XH stretching vibrations in H2O, NH3 and CH4 is considered, based on a morse potential function for the bond stretches plus potential and kinetic energy coupling between pairs of bond oscillators. It is shown that this model can be set up as a matrix in local mode basis functions, or as a matrix in normal mode basis functions, leading to identical results. The energy levels obtained exhibit normal mode patterns at low vibrational excitation, and local mode patterns at high excitation. When the hamiltonian is set up in the normal mode basis it is shown that Darling-Dennison resonances must be included, and simple relations are found to exist between the xrs, gtt, and Krrss anharmonic constants (where the Darling-Dennison coefficients are denoted K) due to their contributions from morse anharmonicity in the bond stretches. The importance of the Darling-Dennison resonances is stressed. The relationship of the two alternative representations of this local mode/normal mode model are investigated, and the potential uses and limitations of the model are discussed.

Local modes and x,K relations for ethene and propadiene

The results recently obtained by Mills and Robiette on local-mode effects in H2O, NH3 and CH4 type molecules are extended to ethene (C2H4) and propadiene (C3H4) type molecules. General relations among the anharmonic xrs constants and the Darling-Dennison Krrss constants for the stretching vibrations are derived, called ���x,K relations���, which allow local-mode effects to be generated by adding the appropriate anharmonic and Darling-Dennison constants to the familiar normal-mode model of molecular vibrations. The general utility of x,K relations is discussed, and the results are reviewed for the molecular types for which they have so far been derived.

Quantitative analysis of remote gas temperatures and concentrations from their infrared emission spectra

Techniques for obtaining quantitative values of the temperatures and concentrations of remote hot gaseous effluents from their measured passive emission spectra have been examined in laboratory experiments and on field trials. These emission spectra were obtained using an adapted FTIR spectrometer with 0.25 cm-1 spectral resolution. The CO2 and H2O vapour content in the plume from a 55 m smoke stack and the temperature of these gases were obtained by comparing the measured emission spectra with those modelled using the HITRAN atmospheric transmission database. The spatial distributions of CO2, CO and unburnt CH4 in a laboratory methane flame were reconstructed tomographically using a matrix inversion technique.

Potential energy surface intersections in triatomic molecules

The different types of surface intersection which may occur in linear configurations of triatomic molecules are reviewed, particularly with regard to the way in which the degeneracy is split as the molecule bends. The Renner-Teller effect in states of symmetry ��, ��, ��, etc., and intersections between �� and ��, �� and ��, and �� and �� states are discussed. A general method of modelling such intersecting potential surfaces is proposed, as a development of the model previously used by Murrell and Carter and co-workers for single-valued surfaces. Some of the lower energy surfaces of H2O, NH2, O3, C3, and HNO are discussed as examples.