High yield syntheses of stable, singly bonded Pd2(6+) compounds

A general method for the syntheses of dipalladium compounds having a singly bonded Pd26+ core and the formula R,S-cis-Pd2(C6H4PPh2)2(O2CR)2Cl2 is described. When the alkyl group in the carboxylate ligands is an electron donating group, the compounds are stable and the yields high. The Pd-Pd distances for the diamagnetic compounds with R = CF3 and CMe3 are 2.5434(4) and 2.5241(9) A, respectively. Calculations at the DFT level suggest that the electronic configuration is sigma2pi4delta2delta*2pi*4. These represent rare examples of palladium(III) compounds.     

Plücker environments, wiring and tiling diagrams, and weakly separated set-systems

For the ordered set [n] of n elements, we consider the class Bn of bases B of tropical Plücker functions on ²[n] such that B can be obtained by a series of so-called weak flips (mutations) from the basis formed by the intervals in [n]. We show that these bases are representable by special wiring diagrams and by certain arrangements generalizing rhombus tilings on an n-zonogon. Based on the generalized tiling representation, we then prove that each weakly separated set-system in ²[n] having maximum possible size belongs to Bn, yielding the affirmative answer to one conjecture due to Leclerc and Zelevinsky. We also prove an analogous result for a hyper-simplex .     

The rearrangement of phosphitohydrazide ligand [(ArO)2P-NPh-NPh-] into iminophosphoranate anion [(PhNP(OAr)2-NPh-] {(ArO)2P = [CH2(BuMeC6H2O)2P]} in coordination sphere of divalent cobalt

The reaction of bromophosphite (ArO)₂PBr {(ArO)₂P = CH₂(6-^tBu-4-Me-C₆H₂O)₂P} with lithium salt of 1,2-diphenylhydrazine gave phosphitohydrazine (ArO)₂P-NPh-NPhH (2) in 64% yield. The last one reacted with Co[N(SiMe₃)₂]₂ to afford cobalt(II) iminophosphoranate (PhNP(OAr)₂-NPh-)₂Co (3), which is the result of isomerisation of the phosphitohydrazide ligand in coordination sphere of divalent cobalt.     

Structure,Stereochemistry and Dynamics of Tetranuclear Polyhydride Clusters Containing Chiral Heterobidentate Phosphanes

A novel chiral phosphane (S)‐2‐(4‐isopropyl‐2‐oxazoline‐2‐yl)phenyl‐di‐N‐pyrrolylphosphane (S‐PyrPOx) based on asymmetric oxazoline ring has been prepared and characterised. Reaction of this ligand and its phenyl‐substituted analogue (S‐PhPOx) with H₄Ru₄(CO)₁₂ and H₃RhOs₃(CO)₁₂ gave substituted derivatives H₄Ru₄(CO)₁₀(1,1‐PhPOx) ( 2 ), H₄Ru₄(CO)₁₀(1,1‐PyrPOx) ( 3 ), and H₃RhOs₃(CO)₁₀(1,1‐PyrPOx) ( 4 ), which were structurally characterised by X‐ray crystallography in solid state and by a variety of multinuclear NMR spectroscopic measurements in solution. In all studied clusters the coordinated ligands form five‐membered chelate rings through phosphorus and nitrogen atoms of oxazoline moiety to afford a novel chiral center associated with the substituted metal atom. The substitution reactions demonstrate extremely high stereoselectivity, which results in formation of only one diastereomer in all three cases to give S,S isomer in 2 and S,R isomer in 3 and 4 .     

Photopolymerization of poly(ethylene glycol) dimethacrylates: The influence of ionic liquids on the formulation and the properties of the resultant polymer materials

The photo‐initiated polymerization of poly(ethylene glycol)dimethacrylates [PEGDM(n)] in the presence of various ionic liquids (ILs) is reported. The influence of ILs concentrations as well as of their nature upon the photopolymerization kinetics was studied in detail. It was found that according to reactive ability in bulk and in solution photopolymerization, the investigated monomers can be divided into two groups: PEGDM(1)–PEGDM(2)–PEGDM(3) and PEGDM(4)–PEGDM(7‐8). ILs slightly influence the photopolymerization of monomers from the first group and greatly change kinetics of those from the second. Such behavior was explained by the theory of “kinetically favorable or unfavorable monomer associations.” It was demonstrated that certain ILs accelerate the photopolymerization of the highest PEGDMs and offer access to the polymers derived from low reactive monomers. Relying on the obtained data, the attempt to predict the structure of the “best” ionic additive for the given monomer photopolymerization was performed and proved. Finally, the influence of both residual and specially added ILs quantities upon the properties of obtained polymer materials was investigated. It was revealed that ILs can physically interact with polymer networks increasing their thermal stability, plasticizing films, and blocks, imparting ionic conductivity equal up to 3.62 × 10^?3 Sm/cm at 25 °C. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2388–2409, 2010     

EPR study of intramolecular dynamics in o-semiquinonic nickel complexes with PCP-pincer ligand in solution

A number of square pyramidal o-semiquinonic nickel complexes with 2,6-bis(diphenylphosphinomethyl)phenyl were investigated by EPR spectroscopy in solution. The complexes have flexible coordination spheres and can exist in solution as two isomers rapidly (on the EPR timescale) interconverting one to another at room temperature. The equilibrium is entropy driven and does not significantly depend on the substituents in the semiquinone ring. The spin density distribution depends on mesomeric properties and bulkiness of substituents in ortho-position to oxygen atoms.     

Tailoring of nanoscale porosity in carbide-derived carbons for hydrogen storage

The poor performance of hydrogen storage materials continues to hinder development of fuel cell-powered automobiles. Nanoscale carbons, in particular (activated carbon, exfoliated graphite, fullerenes, nanotubes, nanofibers, and nanohorns), have not fulfilled their initial promise. Here we show that carbon materials can be rationally designed for H2 storage. Carbide-derived carbons (CDC), a largely unknown class of porous carbons, are produced by high-temperature chlorination of carbides. Metals and metalloids are removed as chlorides, leaving behind a collapsed noncrystalline carbon with up to 80% open pore volume. The detailed nature of the porosity-average size and size distribution, shape, and total specific surface area (SSA)-can be tuned with high sensitivity by selection of precursor carbide (composition, lattice type) and chlorination temperature. The optimum temperature is bounded from below by thermodynamics and kinetics of chlorination reactions and from above by graphitization, which decreases SSA and introduces H2-sorbing surfaces with binding energies too low to be useful. Intuitively, pores of different size and shape should not contribute equally to hydrogen storage. By correlating pore properties with 77 K H2 isotherms from a wide variety of CDCs, we experimentally confirm that gravimetric hydrogen storage capacity normalized to total pore volume is optimized in materials with primarily micropores ( approximately 1 nm) rather than mesopores. Thus, in agreement with theoretical predictions, a narrow size distribution of small pores is desirable for storing hydrogen, while large pores merely degrade the volumetric storage capacity.     

Anodic stripping voltammetry with mercury electrode potential-step and current-step methods

Prof. N. Tanaka (Sendai): (1) What is the difference of this method and the method proposed by Dr. Hickling? (2) How can this method be applied when two substances are present in the solution?Prof.P. Delahay: (1) If I recall correctly hickling in his work recently published [Anal. Chim. Acta, 14 (1956) 297] carries out the anodic oxidation with a stirred amalgam 1 would say that method is quite different from that of hickling. (2) The situation is similar to that in polarography. Both metals are deposited, and the potential first switched at a value at which only the nobler metal is oxidized. A second current-time curve is recorded at a potential at which both metals are oxidized. The concentration of the less noble metal is obtained by difference.Prof. H.A. Laitinen (Urbana): (1) What are the relative sensitivity limits of the potential step and current step methods? (2) Would Prof. Delahay care to comment on the application of these methods with solid microelectrodes? Here no diffusion can occur within the electrode and diffusion in the solution is ill-defined.Prof. P. Delahay: (i) Sensitivities are quite comparable although the potential-step method is more sensitive than the current-step method. (2) These methods can be applied to solid electrodes but a coulometric determination must then be made. Direct evaluation of the concentration from the current-time caracterstics (potential-time curves in the current-step method) is only possible when less than a monolayer is involved (or perhaps a few layers for a non-uniform deposit). See the recent work of nicholson published in J.Am.Chem.Soc.Dr. H. Gerischer (Stuttgart): (t) Wenn ich Sie recht verstanden habe, beruht die grosse Empfindlichkeit der Methode darauf, days eine elektrolitische Trennung und Anerkennung der Untersuchungssubstanz in dem kleinen Hg-Tropfen Erfolgt. (2) Wie wird die Auswertung des anodischen Stromstosses vorgenommen; durch einfache graphische Integration? (3) Glauben Sie nicht, dass die starke Konvektion in der Lösung auch eine Konvektion im Amalgam zur Folge hat, was zu einem weitgehenden Konzentrationsausgleich im Amalgam führen sollte wenn t relativ gross ist?Prof. P. Delahay: (1) The gain in sensitivity is indeed due to the extraction of the metal from the solution into a thin layer of mercury. The metal is deposited into mercury at a rate larger than that at which it can diffuse away. (2) There was no current integration but only direct measurement on the recorded current-time curve. (3) Convection obviously interferes but reproducible conditions can be achieved in analytical applications.Dr. Mechelynck (Mol, Belgique):Dans le cas ou les temps d'électrolyse sont longs, le gain expérimental est supérieur an gain théorique. Je pense qu'au point de vue analytique c'est un avantage, puisque ce phénomène, qui est dû à la sph$\text{'}\text{?}$ericité; de 1'électrode, est parfaitement reproductible si les électrolyses sont effectuées pendant (des temps identiques. Est-ce effectivement le cas?Prof. P. Delahay; Tout à fait d'accord. On est toutefois limité par la solubilité du métal dans le mercure.Prof. W. Kemula (Warsaw): Which substances have you studied? Have you met difficulties with purification of basic electrolytes?Prof. P. Delahay :Our study was limited to the development of some fundamental ideas and their verification and not with the details of application. We studied primarily cadmium. I might add that other metals were studied by nikei.ly and cooke in the work they reported at the Lisbon IUPAC meeting (see recent publication in Anal. Chem.).The purification of the supporting electrolyte is a serious problem. Another problem is the necessity of equilibrating the solution with its container. However, these difficulties are often common to many trace analysis methods.     

Dynamics and conformational properties of Rouse polymers in random layered flows

Here we study the dynamics and the conformational properties of Rouse polymers in random layered flows. We obtain explicit expressions for the mean squared displacement of the center of mass of the polymer as a function of time and number of beads. The averages involve both the thermal noise and the realizations of the random flows. We find also an explicit dependence of the equilibrium value of the end-to-end vector on the number of beads and other dimensional parameters. Our results are compared to that for Rouse polymers immersed in non-random steady shear flows.     

Determination of pore size of catanionic icosahedral aggregates

We show that it is possible to measure the porosity of facetted micron-sized hollow icosahedra of catanionic solutions by performing fluorescence recovery after photobleaching measurements. The size of spontaneous permanent pores in bilayers formed via molecular segregation is compatible with what is observed by freeze-fracture electron microscopy and is discussed versus theoretical expressions of bending energy.