Origin of Ferromagnetism and Magnetic Anisotropy in a Family of Copper(II) Triangles

Previously reported ferromagnetic triangles (NnBu₄)₂[Cu₃(μ₃-Cl)₂(μ-4-NO₂-pz)₃Cl₃] ( 1 ), (PPN)₂[Cu₃(μ₃-Cl)₂(μ-pz)₃Cl₃] ( 2 ), (bmim)₂[Cu₃(μ₃-Cl)₂(μ-pz)₃Cl₃] ( 3 ) and newly reported (PPh₄)₂[Cu₃(μ₃-Cl)₂(μ-4-Ph-pz)₃Cl₃] ( 4 ) were studied by magnetic susceptometry, electron paramagnetic resonance (EPR) spectroscopy and ab initio calculations to assess the origins of their ferromagnetism and of the magnetic anisotropy of their ground S=3/2 state (PPN⁺=bis(triphenylphosphine)iminium, bmim⁺=1-butyl-3-methylbenzimidazolium, pz⁻=pyrazolate). Ab initio studies revealed the d character of the magnetic orbitals of the compressed trigonal bipyramidal copper(II) ions. Ferromagnetic interactions were attributed to weak orbital overlap via the pyrazolate bridges. From the wavefunctions expansions, the ratios of the magnetic couplings were determined, which were indeterminate by magnetic susceptometry. Single-crystal EPR studies of 1 were carried out to extend the spin Hamiltonian with terms which induce zero-field splitting (zfs), namely dipolar interactions, anisotropic exchange and Dzyaloshinskii–Moriya interactions (DMI). The data were treated through both a giant-spin model and through a multispin exchange-coupled model. The latter indicated that ≈62 % of the zfs is due to anisotropic and ≈38 % due to dipolar interactions. The powder EPR data of all complexes were fitted to a simplified form of the multispin model and the anisotropic and dipolar contributions to the ground state zfs were estimated.     

Finitary Spacetime Sheaves

The notion of finitary spacetime sheaves is introduced based on locally finiteapproximations of the continuous topology of a bounded region of a spacetimemanifold. Finitary spacetime sheaves are seen to be sound mathematical modelsof approximations of continuous spacetime observables.     

Selective Isomerization of Epoxides to Allylic Alcohols Catalyzed by TiO2‐Supported Gold Nanoparticles

ReacTiO ₂ ns for rings : Gold nanoparticles supported on TiO₂ are used as a novel heterogeneous catalyst for the isomerization of epoxides to allylic alcohols by a concerted mechanism (see scheme). The reaction proceeds in high yields and the product selectivity is often remarkable.

     

Numerical study of forced and free convective boundary layer flow of a magnetic fluid over a flat plate under the action of a localized magnetic field

The two-dimensional, steady, laminar, forced and free convective boundary layer flow of a magnetic fluid over a semi-infinite vertical plate, under the action of a localized magnetic field, is numerically studied. The magnetic fluid is considered to be water-based with temperature dependent viscosity and thermal conductivity. The study of the boundary layer is separated into two cases. In case I the boundary layer is studied near the leading edge, where it is dominated by the large viscous forces, whereas in case II the boundary layer is studied far from the leading edge of the plate where the effects of buoyancy forces increase. The numerical solution, for these two different cases, is obtained by an efficient numerical technique based on the common finite difference method. Numerical calculations are carried out for the value of Prandl number Pr =  49.832 (water-based magnetic fluid) and for different values of the dimensionless parameters entering into the problem and especially for the magnetic parameter Mn, the viscosity/temperature parameter Θ _r and the thermal/conductivity parameter S*. The analysis of the obtained results show that the flow field is influenced by the application of the magnetic field as well as by the variation of the viscosity and the thermal conductivity of the fluid with temperature. It is hoped that they could be interesting for engineering applications.     

Numerical study of forced and free convective boundary layer flow of a magnetic fluid over a flat plate under the action of a localized magnetic field

The two-dimensional, steady, laminar, forced and free convective boundary layer flow of a magnetic fluid over a semi-infinite vertical plate, under the action of a localized magnetic field, is numerically studied. The magnetic fluid is considered to be water-based with temperature dependent viscosity and thermal conductivity. The study of the boundary layer is separated into two cases. In case I the boundary layer is studied near the leading edge, where it is dominated by the large viscous forces, whereas in case II the boundary layer is studied far from the leading edge of the plate where the effects of buoyancy forces increase. The numerical solution, for these two different cases, is obtained by an efficient numerical technique based on the common finite difference method. Numerical calculations are carried out for the value of Prandl number Pr =  49.832 (water-based magnetic fluid) and for different values of the dimensionless parameters entering into the problem and especially for the magnetic parameter Mn, the viscosity/temperature parameter Θ _r and the thermal/conductivity parameter S*. The analysis of the obtained results show that the flow field is influenced by the application of the magnetic field as well as by the variation of the viscosity and the thermal conductivity of the fluid with temperature. It is hoped that they could be interesting for engineering applications.     

An improved synthesis of diiodonoradamantane

Τhe synthesis of 3,7-diiodo-tricyclo[3.3.1.0^3,7]nonane, the main precursor of noradamantene, by iodination of the corresponding diol via its dimesylate affords a threefold higher yield than the direct iodination of the diol. Neither the dimesylate nor the cyclic sulfate of the diol yields noradamantene upon reduction with sodium amalgam.     

Structural characterization of Elisabatin B and Elisabatin C

X-ray structures of Elisabatin B (1) and Elisabatin C (2) have been determined. Crystal data for 1: Triclinic, P (No. 2), a = 7.528(2) Å, b = 9.404(2) Å, c = 11.414(2) Å, = 75.363(3)°, = 86.668(4)°, = 89.683(4)°, and Z = 2. Crystal data for 2: Monoclinic, P2₁/c (No. 14), a = 8.242(2) Å, b = 14.870(2) Å, c = 13.060(2) Å, = 101.458(3)°, and Z = 4. Both compounds are highly unsaturated leading to extended aromatic conjugation. They show different intermolecular O–HO hydrogen bonds, via which 1 forms dimers, and 2 zig-zag polymeric chains.     

Static and frequency dependent polarizabilities and hyperpolarizabilities of H2Sn

The structure–polarization relationship was investigated in a series of polysulfanes, H₂S_n. The reported results demonstrate that the forms of change of the polarizability components, α_ii, and the second hyperpolarizability components, γ_iiii, as well as the average values α and γ, respectively, of H₂S_n with n are similar. This shows that polarizability components can be easily used to determine corresponding hyperpolarizability data. A remarkable change of the hyperpolarizabilities with the molecular geometry of H₂S_n was found. This result can be used for the design of nonlinear optical materials with optimum properties. The present study uses the flexible σ bonded H₂S_n and is complementary to the works that considered the effect of conformational changes of π-conjugated systems on their hyperpolarizabities. The present computations were performed using the semiempirical approaches MNDO and MNDO/d, as well as ab initio methods with STO-3G, extended with polarization and diffuse functions, and [3s2p/7s5p2d] sets for H₂S_n. At the ab initio level, the electronic and the vibrational contributions to polarizabilities and hyperpolarizabilities were both computed for several members of H₂S_n. The frequency dependence of the above contributions and the static limit were discussed. Electron correlation was taken into account for several test cases using MP2 theory. The selected methods and the variety of the approximations on which they rely allow the systematic consideration of the effect of changes of the geometry of H₂S_n on their polarizabilities and second hyperpolarizabilities. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 1698–1715, 1998