Nano palladium supported on high‐surface‐area metal–organic framework MIL‐101: an efficient catalyst for Sonogashira coupling of aryl and heteroaryl bromides with alkynes

Palladium nanoparticle‐incorporated metal–organic framework MIL‐101 (Pd/MIL‐101) was successfully synthesized and characterized using X‐ray diffraction, nitrogen physisorption, X‐ray photoelectron, UV–visible and infrared spectroscopies, and transmission electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL‐101 and high stability of nano‐size palladium particles. Pd/MIL‐101 nanocomposite was investigated for the Sonogashira cross‐coupling reaction of aryl and heteroaryl bromides with various alkynes under copper‐free conditions. The reusability of the catalyst was tested for up to four cycles without any significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Spherically symmetric static inhomogeneous cosmological models

Spherically symmetric static cosmological models filled with black-body radiation are considered. The models are isotropic about a central observer but inhomogeneous. It is suggested that the energy density of the free gravitational field, which is coupled to the isotropic radiation energy density, might play an important role in generating sufficient field (vacuum) energy (when converted into thermal energy) and initiate processes like inflation. On the central world line the energy density of the free gravitational field vanishes whereas the proper pressure and density of the isotropic black-body radiation are constants. Further, it is shown that the cosmological constant is no more arbitrary but given in terms of the central pressure and density. Also, at its maximum value the energy density of the free gravitational field is proved to be equal to one third of the combined value of radiation pressure and density.     

Effect of heavy quark symmetry on the mass difference ofB-system in minimal left right symmetric model

An estimation of the mass difference of system with heavy quark symmetry formalism is presented. The effective Hamiltonian describing the transition (whereh=b forB _d ⁰ -system) is considered in a manifest left right symmetric (MLRS) model along with contribution from neutral Higgs boson. We use the spin and flavor symmetry for heavy quarks to obtain the transition matrix element 〈B _d ⁰ |ℋ_eff(x)| _d ⁰ 〉 in terms of Isgur-Wise function. Assuming thatB _d ⁰ and states are at rest, we find that Isgur-Wise function turns out to be unity. However using the experimental values of ΔM _K and as input, we find thatM _R=835 GeV andM _H⩾2·9 TeV.     

Model Compounds for Iron Proteins. Structures and Magnetic, Spectroscopic, and Redox Properties of Fe(III)M(II) and [Co(III)Fe(III)](2)O Complexes with (&mgr;-Carboxylato)bis(&mgr;-phenoxo)dimetalate and (&mgr;-Oxo)diiron(III) Cores

A series of heterobimetallic complexes of the type [Fe(III)M(II)L(&mgr;-OAc)(OAc)(H(2)O)](ClO(4)).nH(2)O (2-5) and [{Fe(III)Co(III)L(&mgr;-OAc)(OAc)}(2)(&mgr;-O)](ClO(4))(2).3H(2)O (6) where H(2)L is a tetraaminodiphenol macrocyclic ligand and M(II) = Zn(2), Ni(3), Co(4), and Mn(5) have been synthesized and characterized. The (1)H NMR spectrum of 6 exhibits all the resonances between 1 and 12 ppm. The IR and UV-vis spectra of 2-5 indicate that in all the cases the metal ions have similar coordination environments. A disordered crystal structure determined for 3 reveals the presence of a (&mgr;-acetate)bis(&mgr;-phenoxide)-Ni(II)Fe(III) core, in which the two metal ions have 6-fold coordination geometry and each have two amino nitrogens and two phenolate oxygens as the in-plane donors; aside from the axial bridging acetate, the sixth coordination site of nickel(II) is occupied by the unidentate acetate and that of iron(III) by a water molecule. The crystal structure determination of 6 shows that the two heterobinuclear Co(III)Fe(III) units are bound by an Fe-O-Fe linkage. 6 crystallizes in the orthorhombic space group Ibca with a = 17.577(4) ?, b = 27.282(7) ?, c = 28.647(6) ?, and Z = 8. The two iron(III) centers in 6 are strongly antiferromagnetically coupled, J = -100 cm(-1) (H = -2JS(1).S(2)), whereas the other two S(1) = S(2) = (5)/(2) systems, viz. [Fe(2)(III)(HL)(2)(&mgr;-OH)(2)](ClO(4))(2) (1) and the Fe(III)Mn(II) complex (5), exhibit weak antiferromagnetic exchange coupling with J = -4.5 cm(-1) (1) and -1.8 cm(-1) (5). The Fe(III)Ni(II) (3) and Fe(III)Co(II) (4) systems, however, exhibit weak ferromagnetic behavior with J = 1.7 cm(-1) (3) and 4.2 cm(-1) (4). The iron(III) center in 2-5 exhibits quasi-reversible redox behavior between -0.44 and -0.48 V vs Ag/AgCl associated with reduction to iron(II). The oxidation of cobalt(II) in 4 occurs quasi-reversibly at 0.74 V, while both nickel(II) and manganese(II) in 3 and 5 undergo irreversible oxidation at 0.85 V. The electrochemical reduction of 6 leads to the generation of 4.     

Hydrogen Peroxide/Boric Acid: An Efficient System for Oxidation of Aromatic Aldehydes and Ketones to Phenols

Hydrogen peroxide activated by boric acid in the presence of sulfuric acid has been shown to be an efficient oxidizing system for direct conversion of aromatic aldehydes and ketones to phenols.     

Heck cross-coupling of vinyl heteroaromatic compounds with aryl and heteroaryl halides using Pd(II) complex under phosphine-free conditions

The palladium-catalyzed cross-coupling reaction of vinyl heteroaromatic compounds with aryl bromides and heteroaryl bromides is described using air and moisture stable N,N′,N″,O-tetrafunctional Pd catalyst under phosphine-free conditions. As a result a variety of trans-1,2-disubstituted vinyl heterocycles were obtained in high to good yields.     

Synthesis,molecular and supramolecular structures,electrochemistry and magnetic properties of two macrocyclic dicopper(II) complexes: Microporous supramolecular assembly

Synthesis, molecular and supramolecular structures, electrochemistry and magnetic properties of two diphenoxo-bridged dicopper(II) compounds [Cu^II₂L(H₂O)(ClO₄)]·ClO₄·2H₂O (1) and [Cu^II₂L(N₃)₂]·2H₂O (2) derived from a tetraimino diphenolate macrocyclic ligand H₂L, obtained on [2+2] condensation of 4-methyl-2,6-diformylphenol and 2,2′-dimethyl-1,3-diaminopropane, are presented. Supramolecular structure of both 1 and 2 are three-dimensional resulting from hydrogen bonding interactions. Interestingly, the 3-D self-assembly of 2 contains micropores having the dimension of 0.35 nm. Electrochemical analyses reveal that both of these compounds exhibit two-step couples in the reduction window. Variable-temperature (2–300 K) magnetic susceptibilities measurements of the two compounds reveal that the metal centers in both of the complexes are coupled by strong antiferromagnetic interactions with J values (H = ?JS₁·S₂) ?776 and ?836 cm^?1 for 1 and 2, respectively.     

Optical and dielectric properties of isothermally crystallized nano-KNbO3 in Er3+-doped K2O–Nb2O5–SiO2 glasses

Precursor glass of composition 25K₂O–25Nb₂O₅–50SiO₂ (mol%) doped with Er₂O₃ (0.5 wt% in excess) was isothermally crystallized at 800 °C for 0–100 h to obtain transparent KNbO₃ nanostructured glass–ceramics. XRD, FESEM, TEM, FTIRRS, dielectric constant, refractive index, absorption and fluorescence measurements were carried out to analyze the morphology, dielectric, structure and optical properties of the glass–ceramics. The crystallite size of KNbO₃ estimated from XRD and TEM is found to vary in the range 7–23 nm. A steep rise in the dielectric constant of glass–ceramics with heat-treatment time reveals the formation of ferroelectric nanocrystalline KNbO₃ phase. The measured visible photoluminescence spectra have exhibited green emission transitions of ²H_11/2, ⁴S_3/2 → ⁴I_15/2 upon excitation at 377 nm (⁴I_15/2 → ⁴G_11/2) absorption band of Er³⁺ ions. The near infrared (NIR) emission transition ⁴I_13/2 → ⁴I_15/2 is detected around 1550 nm on excitation at 980 nm (⁴I_15/2 → ⁴I_11/2) of absorption bands of Er³⁺ ions. It is observed that photoluminescent intensity at 526 nm (²H_11/2 → ⁴I_15/2), 550 nm (⁴S_3/2 → ⁴I_15/2) and 1550 nm (⁴I_13/2 → ⁴I_15/2) initially decrease and then gradually increase with increase in heat-treatment time. The measured lifetime (τ_f) of the ⁴I_13/2 → ⁴I_15/2 transition also possesses a similar trend. The measured absorption and fluorescence spectra reveal that the Er³⁺ ions gradually enter into the KNbO₃ nanocrystals.     

Magnetism of Fe in SrFe2As2: Local investigation by time differential perturbed angular distribution (TDPAD) spectroscopy

Employing the γ-ray perturbed angular distribution technique, we have measured the magnetic hyperfine field of ⁵⁴Fe in tetragonal and orthorhombic structural phases of SrFe₂As₂. In the tetragonal phase, the magnetic response of ⁵⁴Fe shows Curie-Weiss type local susceptibility, indicating the presence of localized moment on Fe. The temperature dependence of the hyperfine field of ⁵⁴Fe reflects quasi-two dimensional first order magnetic transition at 200 K. Our data indicate that Fe moments in the magnetically ordered phase of SrFe₂As₂ may be canted out of the ab-plane.