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 reacción entre [RuCl2(dmso)4] y Hbpp (3,5-bis(2-piridil)pirazola). El hecho que sólo tres de los seis posibles estereoisómeros se obtengan a partir de esta reacción, se ha racionalizado en base a factores estructurales y electrónicos. Estos complejos se han caracterizado de forma estructural, espectroscópica y electroquímica. En acetonitrilo en medio básico, el isómero trans,cis-[RuCl2(Hbpp)(dmso)2] da lugar a procesos de isomerización de enlace de un ligando dmso cuando el Ru(II) se oxida a Ru(III). Las constantes termodinámicas y cinéticas para el proceso se han determinado por voltametria cíclica. La irradiación 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 fotosustitución de un ligando dmso por una molécula de acetonitrilo para dar un nuevo compuesto el cual ha sido caracterizado en solución por técnicas espectroscópicas y electroquímicas. Ambos complejos resultan catalizadores útiles en la transferencia de hidrógeno de isopropanol a acetofenona, obteniéndose 1-feniletanol como único producto y un 42.1% de conversión (36.1 ciclos metálicos) a 80ºC con el isómero trans,cis-[RuCl2(Hbpp)(dmso)2], que resulta significativamente más eficaz que el complejo cis(out),cis-[RuCl2(Hbpp)(dmso)2]. La reacción de cis(out),cis-[RuCl2(Hbpp)(dmso)2] con trpy (2,2':6',2"-terpiridina) da lugar a los dos isómeros geométricos del complejo [Ru(Hbpp)(trpy)(Cl)]+, el in y el out. Estos complejos se han aislado y caracterizado por técnicas estructurales, espectroscópicas y electroquímicas. Estos cloro complejos han sido utilizados como precursores para la síntesis de los complejos análogos con ligandos aqua (in,out-[Ru(Hbpp)(trpy)(H2O)]2+) y piridina (in,out-[Ru(Hbpp)(trpy)(py)]2+), los cuales también han sido aislados y caracterizados. Las propiedades ácido-base de los aqua complejos, y del complejo out-py se han estudiado detalladamente por voltametria cíclica y mediante valoraciones espectrofotométricas ácido-base. El tratamiento matemático de los datos así obtenidos nos ha permitido determinar los valores de pKa para los distintos equilibrios de protonación de los complejos en los estados de oxidación II y III. El complejo out-aqua ha demostrado ser un buen catalizador para la oxidación electroquímica del alcohol benzílico, presumiblemente a benzaldehido. La constante de velocidad de segundo orden para el proceso ha sido determinada como 17.1 M-1 s-1, por simulación matemática. El dímero con un puente cloro, [Ru2Cl(bpp)(trpy)2]2+ ha sido preparado por dos rutas sintéticas diferentes. El dímero análogo con un puente acetato se ha obtenido por reacción del cloro dímero con un exceso de acetato sódico. El dímero con dos ligandos aqua [Ru2(bpp)(trpy)2(OH2)2]3+ puede obtenerse por hidrólisis ácida del complejo con un acetato puente o por hidrólisis básica del complejo con un puente cloro. Estos complejos han sido caracterizados por técnicas estructurales, espectroscópicas y electroquímicas. Las soluciones del dímero con dos ligandos aqua en medio ácido resultan inestables a la coordinación de aniones de la solución con el tiempo. Las propiedades ácido-base del dímero con dos aguas coordinadas han sido estudiadas por voltametria cíclica y mediante experimentos de electrólisis a potencial controlado. El pKa para la desprotonación de uno de los ligandos aqua ha sido determinado mediante una valoración espectrofotométrica ácido-base como 6.7. Este valor tan bajo de pKa se atribuye a la formación de la entidad {Ru2O2H3}, favorable termodinámicamente. Los espectros UV-vis para los distintos estados de oxidación del aqua dímero, de RuIIRuII a RuIIIRuIV, han sido obtenidos por oxidación química y electroquímica del complejo. Se han llevado a cabo estudios cinéticos de la oxidación, paso a paso, de RuII,II a RuIV,IV , y se han determinado las constantes de oxidación de segundo orden para los distintos procesos de oxidación. La capacidad del aqua dímero en la oxidación del agua a oxígeno molecular ha sido investigada en solución homogénea utilizando CeIV como oxidante. La evolución de oxígeno se ha demostrado por cromatografia de gases. Se ha obtenido una eficiencia del 73% y 18.6 ciclos catalíticos, cuando 1.83 x 10-6 moles de dímero se han mezclado con un exceso de 100 equivalentes de cerio. El dímero con dos aguas cataliza también la oxidación del agua de forma heterogénea, con el complejo adsorbido sobre una membrana de nafion, aunque la eficiencia es menor. Se ha propuesto un mecanismo intramolecular para la reacción de oxidación del agua. Consiste en la oxidación a 4 electrones del dímero, de RuII,II a RuIV,IV, el cual reacciona con el agua para formar oxígeno y revierte nuevamente al estado de oxidación II,II. Este modelo es consistente con estudios catalíticos de la evolución de oxígeno en función de las concentraciones de cerio y catalizador, llevados a cabo en solución ácida homogénea, que demuestran que la oxidación a 4 electrones del agua se encuentra catalizada por una sola molécula de complejo bajo concentraciones elevadas de cerio. La constante de pseudo-primer-orden para la evolución de oxígeno tiene un valor de 1.4 x 10-2 s-1, que es uno de los valores de constante más elevados obtenidos hasta la fecha. Desafortunadamente, el aqua dímero se desactiva durante el proceso de catálisis dando lugar a una especie naranja, la cual estamos actualmente tratando de caracterizar.

Síntesi, estructura i reactivitat de nous complexos de Cu, Ag i Ni contenint lligands triazamacrocíclics. Aplicacions en l'activació d'enllaços

· S'ha preparat i caracteritzat una família de complexos de Cu(III) contenint lligands triazamacrocíclics, estudiant-se les seves propietats estructurals, espectroscòpiques i redox. Aquesta àmplia família de complexos tenen un gran interès perquè permeten descriure les propietats dels complexos de Cu en un estat d'oxidació poc habitual i a més ens han permès mesurar de manera quantitativa l'efecte Meyerstein. · Una nova família de complexos de Cu(I) amb els lligands triazamacrocíclics es sintetitzada i caracteritzada per tècniques espectroscòpiques i estructurals, demostrant que aquests complexos presenten diferents estructures a l'estat sòlid i en dissolució. Així doncs, mentre que en dissolució es demostra per RMN que es tracta d'una espècie monomèrica, la determinació estructural per difracció de raigs X d'aquests complexos de Cu(I), ens confirma la formació d'espècies polimèriques. Per altra banda, s'ha estudiat la seva reactivitat; a) la seva implicació en la formació de lligands deuterats mitjançant l'intercanvi H/D en condicions suaus i b) la formació de complexos bisfenoxo a partir de la reactivitat entre els corresponents complexos de Cu(I) i oxigen molecular. De la mateixa manera, s'ha preparat el corresponent anàleg de Ag(I) en estat sòlid, obtenint la formació d'un polímer de Ag(I), el qual presenta a l'estat sòlid una estructura en forma de ziga-zaga, diferent a l'estructura del polímer de Cu(I), que és lineal. · S'ha determinat i proposat el mecanisme que té lloc en l'activació de l'enllaç C-H i posterior reacció de transferència per tal d'estabilitzar els productes finals mitjançant una reacció de desproporció. El seguiment de la reacció té lloc mitjançant tècniques espectroscòpiques com UV-vis. Dit seguiment, ens permet determinar les diferents influències electròniques sobre la reacció de formació dels complexos organometàl·lics de Cu(III). A més a més, el seguiment de la reacció a baixa temperatura ens permet determinar espectroscòpica i teòricament la formació d'un intermedi de Cu(II), i mitjançant la determinació dels paràmetres cinètics i termodinàmics es proposa un mecanisme de reacció. Posteriorment, s'ha assajat la reactivitat d'una sal de Cu(II) amb un lligand macrocíclic que conté un grup metil en el carboni orientat cap al centre del macrocicle, implicant la formació d'un intermedi agòstic. De la determinació estructural d'aquest intermedi de CuII i del lligand protonat, s'extreuen una sèrie de conclusions molt interessants, com són la demostració estructural de l'activació de l'enllaç C-C en la primera etapa de formació i de manera anàloga poder comparar-ho amb els sistemes macrocíclics HL2-HL6, demostrant la possible formació d'un intermedi agòstic, on es produeix l'activació de l'enllaç C-H. Aquesta similitud estaria d'acord amb els sistemes HL2-HL6, els quals espectroscòpica i teòricament s'havia detectat la presència d'un intermedi de característiques similars. Degut a l'acidesa d'aquest protó, i gràcies a la presència d'una base com és el propi lligand, aquest podia ésser extret donant lloc a la formació dels corresponents organometàl·lics de Cu(III). Dita estructura també representa un dels pocs exemples d'un organometàl·lic de CuII, un estat d'oxidació poc conegut dins d'aquest camp. · S'ha descrit la reactivitat dels nous complexos organometàl·lics de Cu(III), els quals sota medi pròtic i en condicions àcides o neutres són espècies totalment estables, però en condicions bàsiques o reductores aquestes espècies reaccionen donant lloc a la formació de noves espècies de tipus bisfenoxo, on el Cu es troba en estat d'oxidació +2. S'han caracteritzat mitjançant difracció de RX, on es s'observa l'entorn químic del Cu, la geometria del complex bisfenoxo i l'hidroxilació de l'anell aromàtic. · Finalment, s'ha descrit per primera vegada la síntesi i caracterització d'uns nous complexos organometàl·lics de Ni. Aquests són sintetitzats en base als càlculs teòrics realitzats sobre els nostres sistemes macrocíclics. Per aquests complexos hem investigat l'efecte del metall, canviant el coure per altres metalls de la primera sèrie de transició (Mn, Fe, Co, Ni, Cu, Zn) i de la segona sèrie de transició (Ru, Rh, Pd, Ag). Els resultats demostren que el Ni(II), és el metall que presenta una major capacitat de l'activació de l'enllaç C-H en aquests sistemes aromàtics. Aquests compostos s'oxiden lentament cap a complexos de Ni(III). Per altra banda, l'addició d'una sal de clor sobre una solució d'un complex de Ni(II) permet aïllar el corresponent complex de Ni(III), caracteritzat per ressonància de spin electrònic

Langmuir turbulence and deeply penetrating jets in an unstratified mixed layer

The influence of surface waves and an applied wind stress is studied in an ensemble of large eddy simulations to investigate the nature of deeply penetrating jets into an unstratified mixed layer. The influence of a steady monochromatic surface wave propagating parallel to the wind direction is parameterized using the wave-filtered Craik-Leibovich equations. Tracer trajectories and instantaneous downwelling velocities reveal classic counterrotating Langmuir rolls. The associated downwelling jets penetrate to depths in excess of the wave's Stokes depth scale, δs. Qualitative evidence suggests the depth of the jets is controlled by the Ekman depth scale. Analysis of turbulent kinetic energy (tke) budgets reveals a dynamical distinction between Langmuir turbulence and shear-driven turbulence. In the former, tke production is dominated by Stokes shear and a vertical flux term transports tke to a depth where it is dissipated. In the latter, tke production is from the mean shear and is locally balanced by dissipation. We define the turbulent Langmuir number Lat = (v*/Us)0.5 (v* is the ocean's friction velocity and Us is the surface Stokes drift velocity) and a turbulent anisotropy coefficient Rt = /( + ). The transition between shear-driven and Langmuir turbulence is investigated by varying external wave parameters δs and Lat and by diagnosing Rt and the Eulerian mean and Stokes shears. When either Lat or δs are sufficiently small the Stokes shear dominates the mean shear and the flow is preconditioned to Langmuir turbulence and the associated deeply penetrating jets.

Accumulated metal speciation in earthworm populations with multi-generational exposure to metalliferous soils: cell fractionation and high energy synchrotron analyses

Predicting metal bioaccumulation and toxicity in soil organisms is complicated by site-specific biotic and abiotic parameters. In this study we exploited tissue fractionation and digestion techniques, combined with X-ray absorption spectroscopy (XAS), to investigate the whole-body and subcellular distributions, ligand affinities, and coordination chemistry of accumulated Pb and Zn in field populations of the epigeic earthworm Lumbricus rubellus inhabiting three contrasting metalliferous and two unpolluted soils. Our main findings were (i) earthworms were resident in soils with concentrations of Pb and Zn ranging from 1200 to 27 000 mg kg(-1) and 200 to 34 000 mg kg(-1), respectively; (ii) Pb and Zn primarily accumulated in the posterior alimentary canal in nonsoluble subcellular fractions of earthworms; (iii) site-specific differences in the tissue and subcellular partitioning profiles of populations were observed, with earthworms from a calcareous site partitioning proportionally more Pb to their anterior body segments and Zn to the chloragosome-rich subcellular fraction than their acidic-soil inhabiting counterparts; (iv) XAS indicated that the interpopulation differences in metal partitioning between organs were not accompanied by qualitative differences in ligand-binding speciation, because crystalline phosphate-containing pyromorphite was a predominant chemical species in the whole-worm tissues of all mine soil residents. Differences in metal (Pb, Zn) partitioning at both organ and cellular levels displayed by field populations with protracted histories of metal exposures may reflect their innate ecophysiological responses to essential edaphic variables, such as Ca2+ status. These observations are highly significant in the challenging exercise of interpreting holistic biomarker data delivered by "omic" technologies.

Model catalyst studies of the strong metal-support interaction: Surface structure identified by STM on Pd nanoparticles on TiO2(110)

Model catalysts of Pd nanoparticles and films on TiO2 (I 10) were fabricated by metal vapour deposition (MVD). Molecular beam measurements show that the particles are active for CO adsorption, with a global sticking probability of 0.25, but that they are deactivated by annealing above 600 K, an effect indicative of SMSI. The Pd nanoparticles are single crystals oriented with their (I 11) plane parallel to the surface plane of the titania. Analysis of the surface by atomic resolution STM shows that new structures have formed at the surface of the Pd nanoparticles and films after annealing above 800 K. There are only two structures, a zigzag arrangement and a much more complex "pinwheel" structure. The former has a unit cell containing 7 atoms, and the latter is a bigger unit cell containing 25 atoms. These new structures are due to an overlayer of titania that has appeared on the surface of the Pd nanoparticles after annealing, and it is proposed that the surface layer that causes the SMSI effect is a mixed alloy of Pd and Ti, with only two discrete ratios of atoms: Pd/Ti of 1: 1 (pinwheel) and 1:2 (zigzag). We propose that it is these structures that cause the SMSI effect. (c) 2005 Elsevier Inc. All rights reserved.

Insights into the effects on metal binding of the systematic substitution of five key glutamate ligands in the ferritin of Escherichia coli

Ferritins are nearly ubiquitous iron storage proteins playing a fundamental role in iron metabolism. They are composed of 24 subunits forming a spherical protein shell encompassing a central iron storage cavity. The iron storage mechanism involves the initial binding and subsequent O-2-dependent oxidation of two Fe2+ ions located at sites A and B within the highly conserved dinuclear "ferroxidase center" in individual subunits. Unlike animal ferritins and the heme-containing bacterioferritins, the Escherichia coli ferritin possesses an additional iron-binding site (site C) located on the inner surface of the protein shell close to the ferroxidase center. We report the structures of five E. coli ferritin variants and their Fe3+ and Zn2+ (a redox-stable alternative for Fe2+) derivatives. Single carboxyl ligand replacements in sites A, B, and C gave unique effects on metal binding, which explain the observed changes in Fe2+ oxidation rates. Binding of Fe2+ at both A and B sites is clearly essential for rapid Fe2+ oxidation, and the linking of Fe-B(2+) to Fe-C(2+) enables the oxidation of three Fe2+ ions. The transient binding of Fe2+ at one of three newly observed Zn2+ sites may allow the oxidation of four Fe2+ by one dioxygen molecule.

Metal complexes of a tetraazacyclophane: solution and molecular modelling studies

An alternative synthetic approach to yield the compound 2,3,5,6,8,9,11,14-octahydrobenzo[1][ 1,4,7,10]tetraazacyclotetradecine (bz[14]N-4) is presented. The protonation constants of bz[14]N-4 and the stability constants of its complexes with Ni2+, Cu2+, Zn2+, Cd2+, Pb2+ were determined in H2O at 25degreesC with ionic strength 0.10 mol dm(-3) in KNO3 and they were compared with structurally related macrocycles cyclam (1,4,8,11-tetraazacyclotetradecane) and cyclen (1,4,7,10-tetraazacyclododecane). These studies indicate that only 1 : 1 ( M : L) species are formed in solution, and the ligand exhibits a high affinity for larger ions such as Cd2+ and Pb2+. The X-ray study of [bz[14]N4H3](3+) shows that an inclusion compound with a chloride counter-anion is formed through NH...Cl hydrogen bonds. Spectroscopic data in solution ( electronic and NMR spectra) showed that the macrocycle adopts a planar arrangement upon metal complexation. Molecular mechanics calculations reveal that in spite of the presence of the benzene ring in the macrocyclic framework this ligand can encapsulate metal ions with different stereo-electronic sizes in square planar arrangements. Our results indicate that the presence of the benzene ring in the backbone of the bz[14]N-4 confers a coordination behaviour intermediate between that of cyclam and cyclen.

Dinuclear complexes of M-II thiocyanate (M = Ni and Cu) containing a tridentate Schiff-base ligand: synthesis, structural diversity and magnetic properties

A dinuclear Ni-II complex, [Ni-2(L)(2)(H2O)(NCS)(2)]center dot 3H(2)O (1) in which the metal atoms are bridged by one water molecule and two mu(2)-phenolate ions, and a thiocyanato-bridged dimeric Cull complex, [Cu(L)NCS](2) (2) [L = tridentate Schiff-base ligand, N-(3-aminopropyl)salicylaldimine, derived from 1:1 condensation of salicylaldehyde and 1,3-diaminopropane], have been synthesized and characterized by IR and UV/Vis spectroscopy, cyclic voltammetry and single-crystal X-ray diffraction studies. The structure of 1 consists of dinuclear units with crystallographic C-2 symmetry in which each Ni-II atom is in a distorted octahedral environment. The Ni-O distance and the Ni-O-Ni angle, through the bridged water molecule, are 2.240(11) angstrom and 82.5(5)degrees, respectively. The structure of 2 consists of dinuclear units bridged asymmetrically by di-mu(1,3)-NCS ions; each Cull ion is in a square-pyramidal environment with tau = 0.25. Variable-temperature magnetic susceptibility studies indicate the presence of dominant ferromagnetic exchange coupling in complex 1 with J = 3.1 cm(-1), whereas complex 2 exhibits weak antiferromagnetic coupling between the Cu-II centers with J = -1.7 cm(-1). ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Bending, twisting, and breaking CuCN chains to produce framework materials: the reactions of CuCN with alkali-metal halides

The reactions of the low-temperature polymorph of copper(I) cyanide (LT-CuCN) with concentrated aqueous alkali-metal halide solutions have been investigated. At room temperature, KX (X = Br and I) and CsX (X = Cl, Br, and I) produce the addition products K[Cu-2(CN)(2)Br](H2O)-H-. (I), K-3[Cu-6(CN)(6)I-3](.)2H(2)O (II), Cs[Cu-3(CN)(3)Cl] (III), Cs[Cu-3(CN)(3)Br] (IV), and Cs-2[Cu-4(CN)(4)I-2](H2O)-H-. (V), with 3-D frameworks in which the -(CuCN)- chains present in CuCN persist. No reaction occurs, however, with NaX (X = Cl, Br, I) or KCl. The addition compounds, I-V, reconvert to CuCN when washed. Both low- and high-temperature polymorphs of CuCN (LT- and HT-CuCN) are produced, except in the case of Cs[Cu-3(CN)(3)Cl] (III), which converts only to LT-CuCN. Heating similar AX-CuCN reaction mixtures under hydrothermal conditions at 453 K for 1 day produces single crystals of I-V suitable for structure determination. Under these more forcing conditions, reactions also occur with NaX (X = Cl, Br, I) and KCl. NaBr and KCl cause some conversion of LT-CuCN into HT-CuCN, while NaCl and NaI, respectively, react to form the mixed-valence Cu(I)/Cu(II) compounds [Cu-II(OH2)(4)][Cu-4(I)(CN)(6)], a known phase, and [Cu-II(OH2)(4)][Cu-4(I)(CN)(4)I-2] (VI), a 3-D framework, which contains infinite -(CuCN)- chains. After 3 days of heating under hydrothermal conditions, the reaction between KI and CuCN produces [Cu-II(OH2)(4)][Cu-2(I)(CN)I-2](2) (VII), in which the CuCN chains are broken into single Cu-CN-Cu units, which in turn are linked into chains via iodine atoms and then into layers via long Cu-C and Cu-Cu interactions.

An unprecedented mononuclear double helicate with a square planar metal ion

Reactions of the 1:2 condensate (L) of benzil dihydrazone and 1-methyl-2-imidazole carboxaldehyde with Cd(ClO4)(2)center dot xH(2)O and CdI2 yield [CdL2]( ClO4)(2) (1) and LCdI2 (2), respectively. The yellow ligand L, and its yellow complexes 1 and 2 are characterized by NMR and single crystal X-ray diffraction. Though L contains four N-donor centers, 1 is found to be a four-coordinate double helicate with a square planar Cd(II)N-4 core and 2 a spiral coordination polymer with tetrahedral Cd(II)N2I2 moieties. The bidentate nature of L and the occurrence of the square planar coordination of Cd( II) is explained by DFT calculations. (c) 2007 Elsevier B. V. All rights reserved.

Two new Ni-II complexes with mu(1.5)-dicyanamide as bridging ligand

One 3D and one 2D mu(1,5)-dicyanamide bridged Ni-II complexes having molecular formula [Ni(L1)(dca)(2)] (1) and [Ni-2(L-2)(2)(dca)(4)] (.) 0.5H(2)O (2) (L1 = 4-(2-aminoethyl)-morpholine, L2 = 1-(2-aminoethyl)-piperidine and dca = dicyanamide dianion) have been synthesized. X-ray single crystal analyses and low temperature magnetic measurements were used to characterize the complexes. Complex 1 represents a 3D structure where each metal ion is chelated by morpholine ligand (L1) and connected by four mu(1,5)-dca. Whereas complex 2 shows an undulated 2D structure with grid of (4,4) topology having two crystallographically independent Ni-II centers in similar octahedral environment where each metal center is chelated by one piperidine ligand (L2) and coordinated by four mu(1,5)-dca. Magnetic measurements of both the complexes indicate weak antiferromagnetic interactions through the mu-(1,5)-dca bridging ligands. (c) 2004 Elsevier B.V. All rights reserved.

Syntheses, structural analyses, and magneto-structural correlations of three polymeric Fe(II) complexes with azide ligand

Three new metal-organic polymeric complexes, [Fe(N-3)(2)(bPP)(2)] (1), [Fe(N-3)(2)(bpe)] (2), and [Fe(N-3)(2)(phen)] (3) [bpp = (1,3-bis(4-pyridyl)-propane), bpe = (1,2-bis(4-pyridyl)-ethane), phen = 1,10-phenanthroline], have been synthesized and characterized by single-crystal X-ray diffraction studies and low-temperature magnetic measurements in the range 300-2 K. Complexes 1 and 2 crystallize in the monoclinic system, space group C2/c, with the following cell parameters: a = 19.355(4) Angstrom, b = 7.076(2) Angstrom, c = 22.549(4) Angstrom, beta = 119.50(3)degrees, Z = 4, and a = 10.007(14) Angstrom, b = 13.789(18) Angstrom, c = 10.377(14) Angstrom, beta = 103.50(1)degrees, Z = 4, respectively. Complex 3 crystallizes in the triclinic system, space group P (1) over bar, with a = 7.155(12) Angstrom, b = 10.066(14) Angstrom, c = 10.508(14) Angstrom, alpha = 109.57(1)degrees, beta = 104.57(1)degrees, gamma = 105.10(1)degrees, and Z = 2. All coordination polymers exhibit octahedral Fe(II) nodes. The structural determination of 1 reveals a parallel interpenetrated structure of 2D layers of (4,4) topology, formed by Fe(II) nodes linked through bpp ligands, while mono-coordinated azide anions are pendant from the corrugated sheet. Complex 2 has a 2D arrangement constructed through 1D double end-to-end azide bridged iron(11) chains interconnected through bpe ligands. Complex 3 shows a polymeric arrangement where the metal ions are interlinked through pairs of end-on and end-to-end azide ligands exhibiting a zigzag arrangement of metals (Fe-Fe-Fe angle of 111.18degrees) and an intermetallic separation of 3.347 Angstrom (through the EO azide) and of 5.229 Angstrom (EE azide). Variable-temperature magnetic susceptibility data suggest that there is no magnetic interaction between the metal centers in 1, whereas in 2 there is an antiferromagnetic interaction through the end-to-end azide bridge. Complex 3 shows ferro- as well as anti-ferromagnetic interactions between the metal centers generated through the alternating end-on and end-to-end azide bridges. Complex I has been modeled using the D parameter (considering distorted octahedral Fe(II) geometry and with any possible J value equal to zero) and complex 2 has been modeled as a one-dimensional system with classical and/or quantum spin where we have used two possible full diagonalization processes: without and with the D parameter, considering the important distortions of the Fe(II) ions. For complex 3, the alternating coupling model impedes a mathematical solution for the modeling as classical spins. With quantum spin, the modeling has been made as in 2.

Cu(I) and Ag(I) complexes of chalcogenide derivatives of the organometallic ligand dppf and the dppa analogue

New Cu(I) and Ag(I) complexes were prepared by reaction of [M(NCCH3)(4)][X] (M = Cu or Ag; X = BF4 or PF6) with the bidentate chalcogenide ligands Ph2P(E)NHP(E)Ph-2 (E = S, S(2)dppa; E = Se, Se(2)dppa), and dpspf (1, 1'-bis(diphenylselenophosphoryl)ferrocene). Copper and silver behaved differently. While three molecules of either S(2)dppa and Se(2)dppa bind to a distorted tetrahedral Cu-4 cluster, with deprotonation of the ligand, 1:2 complexes of the neutral ligands are formed with Ag(l), with a tetrahedral coordination of the metal. The [Cu-4{Ph2P(Se)NP(Se)Ph-2}(3)](+) clusters assemble as dimers, held together by weak Se...Se distances interactions. Another dimer was observed for the [Ag(dpspf)](+) cation, with two short Ag...Se distances. DFT and MP2 calculations indicated the presence of attracting interactions, reflected in positive Mayer indices (MI). The electrochemistry study of this species showed that both oxidation and reduction took place at silver. (C) 2004 Elsevier B.V. All rights reserved.

Oxovanadium(V) complexes of bis(phenolate) ligands with acetylacetone as co-ligand: synthesis, crystal structure, electrochemical and kinetics studies on the oxidation of ascorbic acid

Two vanadium(V) complexes, [VO(L-1)]acac)] (1) and [VO(L-2)(acac)] (2), where H2L1 = N,N-bis(2-hydroxy-3-5-di-tert-butyl-benzyl)propylamine and H2L2 = 2,2'-selenobis(4,6-di-tert-butylphenol), have been synthesized and characterized by elemental analyses, IR, V-51 NMR, both in the solid and in solution, and cyclic voltammetric studies. Single crystal X-ray studies reveal that in complex 1 the vanadium atom is octahedrally coordinated with an O5N donor environment, where the oxygen atom of the V-V=O moiety and the N atom of the ONO ligand occupy the axial sites while two oxygen atoms (O1 and O2) from the bisphenolate ligand and two oxygen atoms (O3 and O4) from the acac ligand occupy the equatorial plane. A similar bonding pattern has also been encountered for 2 with the exception that a Se atom instead of N is involved in weak bonding to the metal center. Both complexes showed reversible cyclic voltammeric responses and E-1/2 appears at -0.18 and 0.10 V versus NHE for complexes 1 and 2, respectively. The kinetics of oxidation of ascorbic acid by complex 1 were carried out in 50% MeCN-50% HO (v/v) at 25 degrees C. The high formation constant value, Q = 63 +/- 7 M-1, reveals that the reaction proceeds through the rapid formation of a H-bonded intermediate. The low k(2)Q(2)/k(1)Q(1) ratio (13.4) for 1 points out that there is extensive H-bonding between the oxygen atom of the V-V=O group and the OH group of ascorbic acid. (c) 2007 Published by Elsevier Ltd.

The Crucial Role of Polyatomic Anions in Molecular Architecture: Structural And Magnetic Versatility of Five Nickel(II) Complexes Derived from A N,N,O-Donor Schiff Base Ligand

A series of five Ni(II)-complexes containing the same tridentate Schiff base but different monoanionic ligands (N-3(-), NO3-, PhCOO- and NO2-)reveals that the competitive as well as the cooperative role of the monoanions and phenoxo group in bridging the metal ions play the key role in the variation of molecular architecture.