Doubly Bridged Dinuclear Cadmium(II)azido Schiff Base Complexes: Synthesis, X-Ray Structure and Luminescence Properties of [Cd(L)(N3)]2(Y)2 [L = Schiff Bases, Y = ClO4 −, PF6 −]

Three new Schiff bases, -(bis(pyridin-2-yl)alkylidene)butane-1,4-diamine [(py)(R)C=N-(CH)N=C(R)(py), L: py = pyridine; R = H, -(bis(pyridin-2-yl)formylidene)butane-1,4-diamine (bpfd); R = Me, -(bis(pyridin-2-yl)methylidene)butane-1,4-diamine (bpmd); R = C, -(bis(pyridin-2-yl)bezylidene)butane-1,4-diamine (bpbd)] were prepared and used to synthesize six dinuclear cadmium(II)azido complexes of type [Cd(L)(N)](Y) [L = bpfd, Y = ClO (1a); L = bpfd, Y = PF (1b); L = bpmd, Y = ClO (2a); L = bpmd, Y = PF (2b); L = bpbd, Y = ClO (3a); and L = bpbd, Y = PF (3b)]. Two representative members of the series, 3a and 3b, have been characterized by single crystal X-ray diffraction measurements. Structural study reveals that each cadmium center in both dinuclear compounds is located in a distorted octahedral coordination environment surrounded by six nitrogen atoms—four (N1, N2, N3, N4) from tetradentate ligand, and the fifth and sixth positions occupied by nitrogen atoms (N5, N5^*) of doubly end-on bridging azides. The complexes display intraligand ¹ fluorescence and intraligand ³ phosphorescence in glassy solutions (MeOH at 77 K).     

Liquid-liquid extraction of thorium(IV) and uranium(VI) with three ether-amide type tripodands

N,N,N',N',N',N'-Hexaethyl-2,2′,2'-(nitrilotrisethyleneoxy-2-benzyloxy)tris(acetamide) (L3) has been prepared and characterized by using IR, ¹H NMR and positive-ion FAB mass spectra. The extraction of Th⁴⁺ and UO₂ ²⁺ with N,N,N',N',N',N'-hexaethyl-2,2',2'- (nitrilo-trisethyleneoxy)tris(acetamide) (L1), N,N,N',N',N',N'-hexaisopropyl-2,2',2'-(nitrilotrisethyleneoxy)tris(acetamide) (L2), and L3 was studied at 20±1 °C as a function of diluent, concentration of free extractant in organic phase and concentration of picrate in aqueous phase. It was found that the extracting powers of L1 and L2 for Th⁴⁺ are almost identical. The extracting power of L2 for UO22+ was slightly higher than that of L1. The difference in terminal groups (ethyl or isopropyl) of the extractants (L1 and L2) with same backbone has a little effect on the extracting power for both Th4+ and UO22+. The extracting powers of L3 for both Th4+ and UO22+ were larger than those of L1 and L2. The extractants (L1 and L3) having the same terminal group (ethyl) with different backbones have obviously different extracting powers for Th4+ or UO22+. The extracting powers of all three extractants L1, L2, and L3 for Th4+ were larger than those for UO22+. The compositions of extracted species in organic phase were predominantly ThL(Pic)3NO3 and UO2L(Pic)NO3, respectively (L denotes L1, L2 and L3). This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis,spectral characterisation and redox studies of copper(I) and silver(I) complexes of N(1)-benzyl-2–(arylazo)imidazoles

Complexes of general formula [ML2]ClO4 [M=Cu or Ag; L=N(1)-benzyl-2–(arylazo)imidazole] have been prepared and characterised. Spectroscopic data suggest that the complexes are overall tetrahedral with MN4 coordination spheres. Redox studies show a CuI/II couple of ca. 0.5V versus s.c.e. in MeOH. This revised version was published online in June 2006 with corrections to the Cover Date.     

Chiral activated alkenes induced asymmetric Baylis–Hillman reaction in Me3N/H2O/solvent medium

Chiral‐activated alkenes, L ‐menthyl acrylate and (+)‐N‐α‐phenylethyl acrylamide, induced asymmetric Baylis–Hillman reaction of aromatic aldehydes was realized at 25°C for 7 days in Me₃N/H₂O/solvent homogeneous medium. The corresponding Baylis–Hillman adducts were obtained in good chemical yield with moderate to excellent diastereoselectivity (up to 99% de). © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:317–321, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20209     

Polycondensation of activated L‐valine and L‐leucine esters with various lewis acids

To develop a novel polycondensation method for the preparation of poly (amino acid)s, we screened a transition metal or a rare‐earth triflate as a Lewis acid for the polycondensation of activated amino acid esters in N,N‐dimethylformamide solutions at room temperature. The polymerizations of 4‐nitrophenyl L ‐leucinate ( 1a ) and 4‐nitrophenyl L ‐valinate ( 1b ) scarcely proceeded without any Lewis acid at room temperature. In the presence of 5 mol % metal triflates, especially scandium(III) trifluoromethanesulfonate, the polymerizations of both monomers were promoted effectively. The products, which were collected by the reaction mixture being poured into water, were recognized as poly(L ‐valine)s by Fourier transform infrared spectroscopy, gel permeation chromatography analysis, and ¹H NMR spectroscopy. These results showed that a metal triflate as a Lewis acid could coordinate to a carbonyl oxygen of activated L ‐valinate and L ‐leucinate even in a highly polar solvent, such as N,N‐dimethylformamide; therefore, the polymerizations of activated L ‐valinate and L ‐leucinate were promoted. Because steric hindrance derived from the isobutyl group in 1b was less than that of the isopropyl unit in 1a , the effect of the metals was not as sensitive for the polymerization of 1b . © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 543–547, 2007     

Thermal stability of some azo-derivatives and their complexes

this paper deals with the first investigation concerning the thermal stability of two 1-(2-benzothiazolyl)-3-methyl-4-azo-pyrazil-5-one derivatives and their Cu(II) coordination compounds of type ((C₄H₉)₄N)₂[Cu(L)₂]. The thermal decomposition steps were established. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetics and mechanism of the interaction of pentaammine(pyridine-2-carboxylato)cobalt(III) ions with hexaaquanickel(II) and nickel(II) complexes: the role of chelating ligands

The reversible complexation of the pentaammine(pyridine-2-carboxylato)cobalt(III) ion [N5Co{O2C-(2)-C5H4 N}]2+ [N5=5HN3 and tetraethylenepentaammine (tetren)] with NiIIL(OH2)6-n [L=H2O (N5=tetren); L=bipy, ida2- (iminodiacetate) and nta3- (nitrilotriacetate), N5=5NH3 and tetren] has been investigated by the stopped-flow technique at 20-40 degC, and I= 0.3mol dm-3. At 25degC, the rate constants, kf(dm3 mol-1s-1), DeltaH(kJmol-1) and DeltaS(JK-1mol-1) for the formation of the ternary complexes [(tetren)-CoIII{O2C-(2)-C5H4N} NiIIL(OH2)6-n] are as follows: L=H2O, 530+9, 53+2, -15+7, respectively; L=bipy, 640+30, 37+3, -65+9; L=ida2-, 3900+100, 47+3, -18+11; L=nta3-, 10200+400, 49+1, −2+2. Nickel(II), in the ternary complexes, is chelated by the free pyridyl-N and the carboxylato moiety of the pyridine-2-carboxylate bound to the cobalt centre. The formation rate constant (kf) and the associated activation parameters are relatively insensitive to the N5 moieties for a given ligand L; kf increased in the order: Ni(OH2)62+Ni(bipy)(OH2)42+ Ni(ida)(OH2)3 (nta)(OH2)2-. Data analysis indicated that the mechanism shifted from the dissociative interchange (Id) to the chelation-controlled one, with the decrease of the available sites for coordination in NiIIL(OH2)6−n. The rate constants (kr) for the dissociation of [N5CoIII{O2C-(2)-C5 H4N}NiIIL(OH2) 6-(n+2)] to the parent reactants indicated steric acceleration [krL(5NH3) <krL(tetren)] and followed the trend: krNi(nta)->kr Ni(ida) >krNi(bipy)2+ for both pentaammine substrates. The chelate ring opening rate constants for the ternary complexes were estimated, from which it was apparent that the tetren envelope of cobalt(III) exerted relatively greater steric pressure as compared with 5NH3 in favouring opening up of the chelate ring. This revised version was published online in June 2006 with corrections to the Cover Date.     

Experimental and theoretical investigation of the electronic absorption spectra of 2-H(methyl, methylthio, phenyl)-3,4-dihydro-4-quinazolinylidenecyanoacetic ester

The effect of substituents (Me, SMe, Ph) in position 2 has been studied on the nature of the absorption bands of 2-H-3,4-dihydro-4-quinazolinylidenecyanoacetic esters and a very high sensitivity on the substituent has been detected for the short wave maxima. On the basis of data calculated by the ZINDO/S method the featureless long-wave absorption band was assigned to an electronic transition from HOMO to LUMO caused by charge transfer from fragments of the benzene ring and the N=C—N bond to the >C=C—C=O fragment. Dedicated to Professor L. I. Belen’kii on his 75th birthday. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 227–232, February, 2006.     

Automated calculation of complete Pxy and Txy diagrams for binary systems

An algorithm for the calculation of global phase equilibrium diagrams has been recently developed [M. Cismondi, M.L. Michelsen, Global phase equilibrium calculations: critical lines, critical end points and liquid–liquid–vapour equilibrium in binary mixtures, J. Supercrit. Fluids 39 (2007) 287–295]. It integrates the calculation of critical lines, liquid–liquid–vapour (LLV) lines and critical end points, and was implemented in the software program GPEC: global phase equilibrium calculations [M. Cismondi, D.N. Nuñez, M.S. Zabaloy, E.A. Brignole, M.L. Michelsen, J.M. Mollerup, GPEC: a program for global phase equilibrium calculations in binary systems, in: Proceedings of the CD-ROM EQUIFASE 2006, Morelia, Michoacán, Mexico, October 21–25, 2006; www.gpec.plapiqui.edu.ar]. In this work we present the methods and computational strategy for the automated calculation of complete Pxy and Txy diagrams in binary systems. Being constructed from the points given by the global phase diagram at a specified temperature or pressure, their calculation does not require the implementation of stability analysis.     

Tertiary amine catalyzed polymerizations of α‐amino acid N‐carboxyanhydrides: The role of cyclization

Sarcosine N‐carboxyanhydride, D,L ‐alanine N‐carboxyanhydride, D,L ‐phenylalanine N‐carboxyanhydride, and D,L ‐leucine N‐carboxyanhydride were polymerized with pyridine or N‐ethyldiisopropylamine as the catalyst. With pyridine, cyclic oligo‐ and polypeptides were obtained in addition to water‐initiated or water‐terminated chains. The cyclopeptides were the main products in the case of sarcosine N‐carboxyanhydride and D,L ‐phenylalanine N‐carboxyanhydride. The fraction of cycles was particularly high when N‐methylpyrrolidone was used as the reaction medium. These results suggested the existence of a pyridine‐catalyzed zwitterionic mechanism. However, cyclopeptides were also obtained with N‐ethyldiisopropylamine as the catalyst. In this case, N‐deprotonation of N‐carboxyanhydrides, followed by the formation of N‐acyl N‐carboxyanhydride chain ends, was the most likely initiation mechanism. Various chain‐growth mechanisms were examined. In the case of γ‐benzyl ester‐L ‐glutamate N‐carboxyanhydride, side reactions such as the formation of pyroglutamoyl end groups were detected. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4680–4695, 2006     

Syntheses,characterizations, and crystal structures of tri‐ and diorganotin (IV) derivatives with 2‐mercapto‐5‐methyl‐1,3,4‐thiadiazole

A series of organotin(IV) complexes with 2‐mercapto‐5‐methyl‐1,3,4‐thiadiazole (HL) of the type R₃ Sn(L) (R = Me 1 ; Bu 2 ; Ph 3 ; PhCH₂ 4 ) and R₂Sn(L)₂ (R = CH₃ 5 ; Ph 6 ; PhCH₂ 7 ; Bu 8 ) have been synthesized. All complexes 1–8 were characterized by elemental analysis, IR,¹H, ¹³ C, and ¹¹⁹Sn NMR spectra. Among these, complexes 1 , 3 , 4 , and 7 were also determined by X‐ray crystallography. The tin atoms of complexes 1 , 3 , and 4 are all penta‐coordinated and the geometries at tin atoms of complexes 3 and 4 are distorted trigonal–bipyramidal. Interestingly, complex 1 has formed a 1D polymeric chain through Sn and N intermolecular interactions. The tin atom of complex 7 is hexa‐coordinated and its geometry is distorted octahedral. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:353–364, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20215     

A facile synthesis of 2‐amino‐1,3‐selenazole by reaction of N,N‐unsubstituted selenourea with ketone

2‐Dialkylamino‐1,3‐selenazoles were yielded by the reaction of N,N‐unsubstituted selenoureas with ketones in the presence of ferric chloride. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:88–92, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20180     

Design principles for Brownian molecular machines: how to swim in molasses and walk in a hurricane

Protein molecular motors-perfected over the course of millions of years of evolution-play an essential role in moving and assembling biological structures. Recently chemists have been able to synthesize molecules that emulate in part the remarkable capabilities of these biomolecular motors (for extensive reviews see the recent papers: E. R. Kay, D. A. Leigh and F. Zerbetto, Angew. Chem., Int. Ed., 2006, 46, 72-191; W. R. Browne and B. L. Feringa, Nat. Nanotechnol., 2006, 1, 25-35; M. N. Chatterjee, E. R. Kay and D. A. Leigh, J. Am. Chem. Soc., 2006, 128, 4058-4073; G. S. Kottas, L. I. Clarke, D. Horinek and J. Michl, Chem. Rev., 2005, 105, 1281-1376; M. A. Garcia-Garibay, Proc. Natl. Acad. Sci., U. S. A., 2005, 102, 10771-10776)). Like their biological counterparts, many of these synthetic machines function in an environment where viscous forces dominate inertia-to move they must "swim in molasses". Further, the thermal noise power exchanged reversibly between the motor and its environment is many orders of magnitude greater than the power provided by the chemical fuel to drive directed motion. One might think that moving in a specific direction would be as difficult as walking in a hurricane. Yet biomolecular motors (and increasingly, synthetic motors) move and accomplish their function with almost deterministic precision. In this Perspective we will investigate the physical principles that govern nanoscale systems at the single molecule level and how these principles can be useful in designing synthetic molecular machines.     

Theoretical study of the red‐ and blue‐shifted hydrogen bonds of nitroxyl and acetylene dimers

Ab initio molecular orbital and density functional theory (DFT) in conjunction with different basis sets calculations were performed to study the C? H…O red‐shifted and N? H…π blue‐shifted hydrogen bonds in HNO? C₂H₂ dimers. The geometric structures, vibrational frequencies and interaction energies were calculated by both standard and counterpoise (CP)‐corrected methods. In addition, the G3B3 method was employed to calculate the interaction energies. The topological and natural bond orbital (NBO) analysis were investigated the origin of N? H…π blue‐shifted hydrogen bond. From the NBO analysis, the electron density decrease in the σ* (N? H) is due to the significant electron density redistribution effect. The blue shifts of the N? H stretching frequency are attributed to a cooperative effect between the rehybridization and electron density redistribution. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

The effect of the concentration of platinum nanocolloid stabilizer on the rate of catalytic reactions in aqueous solution

The reduction of methyl viologen with hydrogen in the presence of NaOH and neptunium (VI) ions with formic acid in aqueous solutions catalyzed by platinum nanocolloids is studied. It is established that the rate of reaction with the participation of methyl viologen exponentially decreases with an increase in the concentration of a colloid stabilizer (sodium polyacrylate). The rate of neptunium reduction catalyzed by platinum nanoparticles of various sizes also decreases with an increase in the polyacrylate concentration to 4 × 10⁻³ M. A further increase in the content of stabilizer leads to some acceleration of the reaction. The mechanism of the effect of the stabilizer concentration on the catalytic activity of platinum nanocolloids is discussed. Original Russian Text ? B.G. Ershov, A.V. Anan’ev, N.L. Sukhov, 2006, published in Kolloidnyi Zhurnal, 2006, Vol. 68, No. 2, pp. 172–179.     

Simple and efficient synthesis of new chiral N,N′‐sulfonyl bis‐oxazolidin‐2‐ones

A series of new chiral N,N′‐sulfonyl bis‐oxazolidin‐2‐ones were synthesized starting from 2‐aminoalcohols, sulfuryl chloride, and diethyl carbonate. This method utilizes natural amino acids as a source of chirality for the preparation of oxazolidinones. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:61–65, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20183     

Design,Synthesis, and Structural Analysis of Divalent NI Compounds and Identification of a New Electron‐Donating Ligand

The dative‐bond representation (L→E) in compounds with main group elements (E) has triggered extensive debate in the recent past. The scope and limits of this nonclassical coordination bond warrant comprehensive exploration. Particularly compounds with (L→N←L′)⁺ arrangement are of special interest because of their therapeutic importance. This work reports the design and synthesis of novel chemical species with the general structural formula (L→N←L′)⁺ carrying the unusual ligand cyclohexa‐2,5‐diene‐4‐(diaminomethynyl)‐1‐ylidene. Four species belonging to the (L→N←L′)⁺ class carrying this unconventional ligand were synthesized. Quantum chemical and X‐ray diffraction analyses showed that the electronic and geometric parameters are consistent with those of already reported divalent N^I compounds. The molecular orbital analysis, geometric parameters, and spectral data clearly support the L→N and N←L′ interactions in these species. The newly identified ligand has the properties of a reactive carbene and high nucleophilicity.     

Synthesis,characterization, and immobilization of nickel(II) tetradentate Schiff-base complexes on clay as heterogeneous catalysts for the oxidation of cyclooctene

Nickel(II) tetradentate Schiff-base complexes of N,N′-(bis(pyridin-2-yl)formylidene)ethane-1,2-diamine (L1), N,N′-(bis(pyridin-2-yl)formylidene)cyclohexane-1,2-diamine (L2), N,N′-(bis(pyridin-2-yl)formylidene)benzene-1,2-diamine (L3), N,N′-(bis(pyridin-2-yl)formylidene)meso-stilben-1,2-diamine (L4), and N,N′-(bis(pyridin-2-yl)formylidene)propane-1,3-diamine (L5) were synthesized, characterized, and immobilized on sodium montmorillonite. The complexes were characterized by IR spectroscopy, diffuse reflectance spectra (DRS), and atomic absorption spectroscopy (AAS). IR and DRS data of the heterogeneous catalysts show that the Ni(II) complexes were physically entrapped within the sodium montmorillonite clay. The supported complexes show good catalytic activity for the epoxidation of cyclooctene using tert-butylhydroperoxide (TBHP) as oxygen source in acetonitrile. The Ni-catalyzed oxidation proceeds with 62.3% selectivity for epoxidation with 69% conversion for supported [Ni(L5)].     

Synthesis,characterization, optical and anti-bacterial properties of benzothiazole Schiff bases and their lanthanide (III) complexes

Two new Schiff base ligands comprising benzothiazole derivatives, namely (N,N′,E,N,N′E)-N,N′-(1,3-phenylenebis(methanylylidene))bis(5-nitrobenzo[d]thiazoL2-amine (L1) and (N,N′,E,N,N′E)-N,N′-(1,3-phenylene-bis(methanylylidene))bis(5-methylthiazo-L2-amine (L2), have been synthesized and thoroughly characterized using FTIR, ¹H NMR, mass UV/vis and fluorescence spectral techniques. Further, L1 and L2 lead to the formation of lanthanide complexes 1–6 with Ce(III), Nd(III), and Pr(III) ions in 1:2 (metal:ligand) stoichiometry. UV/vis spectra of L1, L2 and 1–6 exhibit characteristic ligand centered absorptions in the range of 230–350 nm. Besides, both ligands and complexes show significant emissions and good anti-bacterial activity against pathogenic bacteria. Ligands and complexes display anti-bacterial activity against bacteria Staphylococcus aureus (S. aureus) (MTCC 1144) causing skin infection and food poisoning and pimple-causing bacteria propionic bacteria acnes (P. acnes) (MTCC 1951).