Square planar complexes of Cu(II) and Ni(II) with N<Subscript>2</Subscript>O donor set of two Schiff base ligands: synthesis and structural aspects

Abstract Two new square planar Cu(II) and Ni(II) complexes, [CuL¹(NCO)] (1) and [NiL²(N₃)] (2) have been synthesized with two different tridentate N₂O donor Schiff base ligands L ¹ H (1:1 condensation product of benzoylacetone and 2-diethylaminoethylamine) and L ² H (1:1 condensation product of benzoylacetone and 2-dimethylaminoethylamine), respectively. Both the complexes 1 and 2 have been characterized by elemental analysis, IR, UV-Vis spectroscopy, room temperature magnetic susceptibility measurement, electrochemical, thermal, and single crystal X-ray diffraction studies. Structural studies reveal that in both the complexes metal centers have square planar environment with N₂O donor set of Schiff base ligands and terminal pseudohalide anions (isocyanate for 1 and azide for 2) at four coordination sites of square plane. Graphical abstract Square planar complexes of Cu(II) and Ni(II) with N ₂ O donor set of two Schiff base ligands: synthesis and structural aspects Subhra Basak, Soma Sen, Samiran Mitra, C. Marschner, W. S. Sheldrick Two new square planar Cu(II) and Ni(II) complexes, [CuL¹(NCO)] (1) and [NiL²(N₃)] (2) have been synthesized with two different tridentate N₂O donor Schiff base ligands L ¹ H and L ² H respectively. Both the complexes 1 and 2 have been characterized by elemental analysis, IR, UV-Vis spectroscopy, room temperature magnetic susceptibility measurement, electrochemical, thermal and single crystal X-ray diffraction studies.      

Silber

Ohne Zusammenfassung     

Thermal conductivity and thermal Hall effect in Bi- and Y-based high-T c superconductors

Measurements of the thermal conductivity (k_xx) and the thermal Hall effect (k_xy) in high magnetic fields in Y- and Bi-based high-T _c superconductors are presented. We describe the experimental technique and test measurements on a simple metal (niobium). In the high-T _c superconductors k_xx and k_xy increase below T _c and show a maximum in their temperature dependence. k_xx has contributions from phonons and quasiparticle (QP) excitations, whereas k_xy is purely electronic. The strong increase of k_xy below T _c gives direct evidence for a strong enhancement of the QP contribution to the heat current and thus for a strong increase of the QP mean free path. Using k_xy and the magnetic field dependence of k_xx we separate the electronic thermal conductivity ( k _xx ^el ) of the CuO ₂ -planes from the phononic thermal conductivity ( k _xx ^ph ). In YBa₂Cu₃O _{7 - δ} k _xx ^el shows a pronounced maximum in the superconducting state. This maximum is much weaker in Bi₂Sr₂CaCu₂O _{8 + δ} , due to stronger impurity scattering. The maximum of k _xx ^el is strongly suppressed by a magnetic field, which we attribute to the scattering of QPs on vortices. An additional magnetic field independent contribution to the maximum of k_xx occurs in YBa₂Cu₃O _{7 - δ} , reminiscent of the contribution of the CuO-chains, as determined from the anisotropy in untwined single crystals. Our data analysis reveals that below T _c as in the normal state a transport (τ) and a Hall ( ) relaxation time must be distinguished: The inelastic (i.e. temperature dependent) contribution to τ is strongly enhanced in the superconducting state, whereas displays the same temperature dependence as above T _c . We determine also the electronic thermal conductivity in the normal state from k_xy and the electrical Hall angle. It shows an unusual linear increase with temperature. Received 23 August 2000     

Coordination chemistry of cyclic disilylated stannylenes and plumbylenes to group 4 metallocenes

Reduction of group 4 metallocene dichlorides with magnesium in the presence of cyclic disilylated stannylene or plumbylene phosphine adducts yielded the respective metallocene tetrylene phosphine complexes. Under the same conditions the use of the respective dimerized stannylene or plumbylene gave metallocene ditetrylene complexes. A computational analysis of these reactions revealed for all investigated compounds multiple-bonded character for the M-E(II) linkage, which can be rationalized in the case of the monotetrylene complex with the classical σ-donor/π-acceptor interaction. The strength of the M-E(II) bond increases descending group 4 and decreases going from Sn to its heavier congener Pb. The weakness of the Ti-E(II) bonds is caused by the significantly reduced ability of the titanium atom for d-p π-back-bonding.     

Role of spin-flip transitions in the anomalous Hall effect of FePt alloy

We carry out ab?initio calculations which demonstrate the importance of the non-spin-conserving part of the spin-orbit interaction for the intrinsic anomalous Hall conductivity of ordered FePt alloys. The impact of this interaction is strongly reduced if Pt is replaced by the lighter isoelectronic element Pd. An analysis of the interband transitions responsible for the anomalous velocity reveals that spin-flip transitions occur not only at avoided band crossings near the Fermi level, but also between well-separated pairs of bands with similar dispersions. We also predict a strong anisotropy in the anomalous Hall conductivity of FePt caused entirely by low-frequency spin-flip transitions.     

Origin of the planar Hall effect in nanocrystalline Co60Fe20B20

An angle dependent analysis of the planar Hall effect (PHE) in nanocrystalline single-domain Co(60)Fe(20)B(20) thin films is reported. In a combined experimental and theoretical study we show that the transverse resistivity of the PHE is entirely driven by anisotropic magnetoresistance (AMR). Our results for Co(60)Fe(20)B(20) obtained from first principles theory in conjunction with a Boltzmann transport model take into account the nanocrystallinity and the presence of 20 at.?% boron. The ab initio AMR ratio of 0.12% agrees well with the experimental value of 0.22%. Furthermore, we experimentally demonstrate that the anomalous Hall effect contributes negligibly in the present case.     

The Combination of Cross-Hyperconjugation and σ-Conjugation in 2,5-Oligosilanyl Substituted Siloles

Reaction of a 2,5-dilithiated silole with excess dichlorodimethylsilane gives the respective 2,5-bis(chlorodimethylsilyl) substituted silole. This compound can be converted to 2,5-bis(oligosilanyl) substituted siloles by addition of a suitable oligosilanide. In the UV spectra of the thus obtained compounds the lowest energy absorptions are bathochromically shifted compared to the absorptions of the two constituents, namely the 2,5-disilyl substituted silole and a trisilane. The bathochromic shift is interpreted as being caused by a mixed σ-conjugation/cross-hyperconjugation. This assumption is supported by TD-DFT calculations, which show a significant contribution from Si−Si bonds to the HOMO of the molecule.     

Photoconductivity in Metal–Organic Framework (MOF) Thin Films

Photoconductivity is a characteristic property of semi‐conductors. Herein, we present a photo‐conducting crystalline metal–organic framework (MOF) thin film with an on–off photocurrent ratio of two orders of magnitude. These oriented, surface‐mounted MOF thin films (SURMOFs), contain porphyrin in the framework backbone and C₆₀ guests, loaded in the pores using a layer‐by‐layer process. By comparison with results obtained for reference MOF structures and based on DFT calculations, we conclude that donor–acceptor interactions between the porphyrin of the host MOF and the C₆₀ guests give rise to a rapid charge separation. Subsequently, holes and electrons are transported through separate channels formed by porphyrin and by C₆₀, respectively. The ability to tune the properties and energy levels of the porphyrin and fullerene, along with the controlled organization of donor–acceptor pairs in this regular framework offers potential to increase the photoconduction on–off ratio.