PEG‐DIL‐based MnCl42−: A novel phase transfer catalyst for nucleophilic substitution reactions of benzyl halides

Poly(ethylene glycol) dicationic ionic liquid‐based MnCl₄^2? was prepared by nucleophilic substitution of poly(ethylene glycol) dichloride with methylimidazole followed by reaction with MnCl₂. The structural properties of the catalyst were systematically investigated using Fourier transform infrared, UV–visible and Raman spectra and thermogravimetric analysis. The application of this catalyst allows the synthesis of a variety of benzyl thiocyanates and azides in high yield under reflux conditions in water. The main advantages of this method are its easy nature, rapidity, environmental benignity and high yields.     

Modulation of fluorescence emission of 1-(2-pyridyl) pyrazole derived Schiff base ligands by exploiting their metal ion sensitive binding modes

Dioxomolybdenum(VI) complexes [MoO₂(B¹)H₂O] (1), [MoO₂(B²)EtOH] (2), [MoO₂(B³)EtOH] (3) and [MoO₂(B⁴)EtOH] (4) were synthesized using the Schiff base ligands H₂B¹(previously reported), H₂B², H₂B³ and H₂B⁴, respectively. These ligands were prepared by condensation of 1-(2-pyridyl) 5-methyl 3-pyrazole carbohydrazide with salicylaldehyde, o-hydroxy acetophenone, 5-bromo salicylaldehyde and 5-nitro salicylaldehyde respectively. Due to the presence of a substituted 1-(2-pyridyl) pyrazole unit, ligands H₂B¹, H₂B² and H₂B³ exhibit fluorescent emissions, and the most intense emission was obtained for H₂B³. H₂B⁴ is incapable of showing fluorescence emission. As the ligands are capable of using different binding modes, according to the demands of the guest metal ions, their emission properties also change accordingly. The dioxomolybdenum(VI) complex of the ligand H₂B¹, i.e. complex 1, shows quenched emission compared to H₂B¹. Again when Cu²⁺, Co²⁺ or Ni²⁺ ions are added to a solution of 1, in each case a new complex of Cu²⁺ Co²⁺ or Ni²⁺ is formed in solution and further quenching was observed. However, with Zn²⁺ input to a solution of 1, fluorescence recovery was observed up to the level of the free ligand. The copper(II) complex of H₂B¹ (complex 5), produced by adding equivalent amount of Cu²⁺ salt to a solution of 1, was isolated and characterized. One of the dioxomolybdenum(VI) complexes, 3, when subjected to an oxo-transfer reaction with PPh₃ produces complex [MoO(B³)CH₃CN] (6). Complex 6 shows reduced fluorescence emissions compared to 3 in the solid phase. These observations open up the possibilities for these ligands to work as fluorescent signaling system with different metal ion inputs. All the complexes are characterized by elemental analyses, electronic spectra, IR, ¹H NMR, magnetic measurements, EPR and by cyclic voltammetry. Complexes 1 and 5, as well as the ligands H₂B² and H₂B³, have been crystallographically characterized.     

Bianchi type-I string cosmological model in the presence of a magnetic flux: exact and qualitative solutions

A Bianchi type-I cosmological model in the presence of a magnetic flux along a cosmological string is investigated. The objective of this study is to generate solutions to the Einstein equations using a few tractable assumptions usually accepted in the literature. The analytical solutions are supplemented with numerical and qualitative analysis. In the frame of the present model the evolution of the Universe and other physical aspects are discussed.     

A characterization of block graphs

A block graph is a graph whose blocks are cliques. For each edge e=uv of a graph G, let N_e(u) denote the set of all vertices in G which are closer to u than v. In this paper we prove that a graph G is a block graph if and only if it satisfies two conditions: (a) The shortest path between any two vertices of G is unique; and (b) For each edge e=uv∈E(G), if x∈N_e(u) and y∈N_e(v), then, and only then, the shortest path between x and y contains the edge e. This confirms a conjecture of Dobrynin and Gutman [A.A. Dobrynin, I. Gutman, On a graph invariant related to the sum of all distances in a graph, Publ. Inst. Math., Beograd. 56 (1994) 18-22].     

First‐Row Transition‐Metal–Diborane and –Borylene Complexes

A combined experimental and quantum chemical study of Group 7 borane, trimetallic triply bridged borylene and boride complexes has been undertaken. Treatment of [{Cp*CoCl}₂] (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) with LiBH₄ ? thf at ?78 °C, followed by room‐temperature reaction with three equivalents of [Mn₂(CO)₁₀] yielded a manganese hexahydridodiborate compound [{(OC)₄Mn}(η⁶‐B₂H₆){Mn(CO)₃}₂(μ‐H)] ( 1 ) and a triply bridged borylene complex [(μ₃‐BH)(Cp*Co)₂(μ‐CO)(μ‐H)₂MnH(CO)₃] ( 2 ). In a similar fashion, [Re₂(CO)₁₀] generated [(μ₃‐BH)(Cp*Co)₂(μ‐CO)(μ‐H)₂ReH(CO)₃] ( 3 ) and [(μ₃‐BH)(Cp*Co)₂(μ‐CO)₂(μ‐H)Co(CO)₃] ( 4 ) in modest yields. In contrast, [Ru₃(CO)₁₂] under similar reaction conditions yielded a heterometallic semi‐interstitial boride cluster [(Cp*Co)(μ‐H)₃Ru₃(CO)₉B] ( 5 ). The solid‐state X‐ray structure of compound 1 shows a significantly shorter boron–boron bond length. The detailed spectroscopic data of 1 and the unusual structural and bonding features have been described. All the complexes have been characterized by using ¹H, ¹¹B, ¹³C NMR spectroscopy, mass spectrometry, and X‐ray diffraction analysis. The DFT computations were used to shed light on the bonding and electronic structures of these new compounds. The study reveals a dominant B?H?Mn, a weak B?B?Mn interaction, and an enhanced B?B bonding in 1 .     

Reduced sampling and incomplete sensitivity for low‐complexity robust parametric optimization

The paper considers robust parametric optimization problems using multipoint formulations and makes the link with momentum‐based formulations. Optimal sampling issues are discussed, and a procedure is proposed to quantify the confidence level on the robustness of the design. We also discuss incomplete sensitivity evaluations to take into account the computational complexity constraint. This permits to take advantage of what was previously developed for efficient monopoint design where the cost of the optimization is comparable with one state evaluations. The proposed algorithm is fully parallel and the time‐to‐solution is comparable with monopoint situations. Concepts are introduced through simple examples, and the paper ends with the design of the shape of an aircraft robust over a range of transverse winds.Copyright © 2013 John Wiley & Sons, Ltd.     

Thermodynamics of the GaCl3-HCl-H2O System at 25°C

A comprehensive equation for the thermodynamic properties of the systemGaCl₃-HCl-H₂O at 25°C in the ion-interaction (Pitzer) equation form has been generatedon the basis of a recent and comprehensive array of electrochemical cellmeasurements of the HCl activity at total stoichiometric ionic strengths from 0.01 to 3.0mol-kg^–1. Alternate equations with and without explicit consideration of thehydrolyzed product GaOH²⁺ as a separate species have been tested. Excellentagreement is obtained between the calculated and measured cell potentials forthe formulation, which includes GaOH²⁺ as an additional species. The effect offurther hydrolysis as well as that of complex formation has been found to benegligible. While a satisfactory set of Pitzer parameters has been found, it wasnot possible to obtain a unique thermodynamic representation for this systembecause of large uncertainties in the first hydrolysis constant of Ga(III) and becauseof redundancies and intrinsic correlations between some of the Pitzer parameters.Deceased December 26, 1997     

Polyethylene Glycol Functionalized Magnetic Dicationic Ionic Liquids as a Novel Catalyst and Their Application in Ring Opening of Epoxides in Water

A simple and environmentally benign protocol for the aqueous synthesis of 1,2‐azidoalcohols via regioselective ring opening of 1,2‐epoxides using PEG‐MDIL as a novel magnetic phase transfer catalyst is described. The catalyst was studied by UV spectroscopy, IR spectroscopy, and thermogravimetric analysis. The reactions occur in water and furnish the corresponding azidoalcoholes in high yields. No evidence for the formation of by‐product and the products were obtained in pure form without further purification.