Magnetism tuned by intercalation of various metal ions in coordination polymer

Insertion of various metal ions have changed the ferromagnetic coordination frameworks into paramagnetic, superparamagnetic, or ferromagnetic. The net charge and radius of the ions determined the magnetism of the host frameworks.     

新型磁性Fe3O4/EDTA复合纳米粒子的制备及性能研究

采用氨羧络合剂EDTA对纳米磁性Fe3O4粒子进行表面改性,制备出能够螯合金属离子和放射性核素离子的磁性Fe3O4/EDTA复合纳米粒子.用X射线衍射、红外光谱、透射电子显微镜、光电子能谱、振动样品磁强计和原子吸收光谱对复合粒子进行了表观形貌、结构、磁学及螯合性能表征.结果表明,纳米磁性Fe3O4和EDTA之间能够有效地以化学键合方式进行复合.改性后,Fe3O4/EDTA纳米复合粒子可以对包括放射性金属离子在内的多种金属离子具有良好的络合效果.     

The binary gallide Eu5Ga9 - crystal structure, chemical bonding and physical properties

The title compound was prepared from the elements by reaction in a sealed tantalum tube at 1320 K followed by slow cooling to 970 K or, alternatively, in glassy carbon crucibles with HF melting. The crystal structure of Eu₅Ga₉ was refined from single-crystal data: Cmcm, a=4.613(1) Å, b=10.902(3) Å, c=26.097(6) Å, Z=4, R_F=0.036, 811 structure factors and 46 variables. The structure is described as a three-dimensional network formed by gallium atoms with europium atoms embedded in the cavities. The bonding analysis (LMTO, ELF) confirmed this representation of the structure. Magnetic susceptibility measurements show Curie-Weiss behavior above 60 K with a magnetic moment per Eu atom of 8.12(1) μ_B, indicating divalent europium. Eu₅Ga₉ orders antiferromagnetically at 19.0(5) K with re-ordering at 6.0(5) K. The electrical resistivity shows a metallic temperature dependence and magnetic scattering. ¹⁵¹Eu Mössbauer spectroscopic experiments are compatible with divalent europium and show complex magnetic hyperfine field splitting below the ordering temperature.     

Synthesis, crystal structure, spectroscopy and magnetic properties of a dinuclear Cu complex with 3,5-bis(2-pyridyl)pyrazole bridging ligand

A dinuclear Cu^II complex [Cu₂(bpp)₂(H₂O)₂](ClO₄)₂ (1) with 3,5-bis(2-pyridyl)pyrazole (Hbpp), has been synthesized and characterized by elemental analyses, thermal analysis, conductance, UV-vis and IR spectra. The crystal structure of 1, determined by X-ray diffraction technique, reveals that two centrosymmetric Cu^II centers are bridged by a pair of tetradentate anionic bpp ligands, adopting a square-pyramidal environment with the water ligand occupying the axial site. An interesting feature of this structure is the formation of a two-dimensional supramolecular network through O-H?O hydrogen bonds between the water moieties of the cationic [Cu₂(bpp)₂(H₂O)₂]²⁺ subunits and perchlorate anions. The magnetic properties of 1 have been investigated by variable-temperature magnetic susceptibility and EPR measurements. Very strong antiferromagnetic interaction between the Cu^II centers (with H=−JS₁S₂, J=−368.3 cm⁻¹) has been observed, and the magneto-structural correlations was analyzed.     

Octaisopropylchromocen: Das erste Chromocen mit kontinuierlichem low spin/high spin-Übergang

Octaisopropylchromocene: The First Chromocene with Gradual low spin/high spin-Transition Octaisopropylchromocene ( 1 ) exists in a low spin state at very low temperatures and undergoes a gradual spin transition on warming up. At 300 K a high spin state with four unpaired electrons has been found for solid 1 by investigation of its magnetic properties.     

Structure and magnetic properties of a copper(II) compound with syn–anti carboxylato- and linear Cu–Cl–Cu chloro-bridges

The copper(II) polymer Cu(2-qic)Cl (2-qic = quinoline-2-carboxylate) was synthesized and then characterized by X-ray crystal structure determination, spectroscopic and magnetic studies. The crystal structure consists of copper(II) ions with two different chromophores: four-coordinated in a square-planar geometry and five-coordinated in an environment between square-pyramidal and trigonal-bipyramidal. The copper ions are bridged sequentially through the carboxylate groups in a syn–anti conformation, forming an infinite one-dimensional zigzag chain with two alternating non-equivalent copper(II) chromophores. The chloride atom acts as a single chloro-bridge link to adjacent chains, forming a ribbon type structure (1D). The variable-temperature (1.8–300 K) magnetic susceptibility data of the complex were interpreted with the dimer law using the molecular field approximation. The results obtained indicate a very weak ferromagnetic (J₂ = 0.37 cm⁻¹) interchain interaction through the syn–anti carboxylate bridge. A relatively strong antiferromagnetic interaction, transmitted through the chloro-bridge with an exchange coupling of J₁ = −57.0 cm⁻¹, dominates the magnetic properties of this complex. The magnitude and the nature of the exchange coupling are explained on the basis of the structural results.     

Metal bis-1,2-dithiolene complexes in conducting or magnetic crystalline assemblies

Crystalline materials studied for their conducting or magnetic properties based on metal complexes of 1,2-dithiolene ligands are discussed emphasising the wide diversity of ligands now available and the variety of materials prepared from these. Complexes have been prepared using electronically delocalised dithiolene ligands where the core complex is extended with units such as thioethers, aromatics, tetrathiafulvalene (TTF) and other heterocycles to explore the influence of these variations on the solid-state structures and properties derived from them. Although superconductivity in dithiolene complexes has so far been limited to [M(dmit)₂]^X− salts, other ligand systems have given rise to numerous conducting and metallic salts and have proven informative in rationalising the criteria for design of the molecular units. Novel material properties have been observed in systems such as hybrid conducting ∣ magnetic materials and mixed dithiolene-metallocene salts. In particular, highly conducting and metallic single-component materials have recently been found uniquely within materials based on metal-bis-1,2-dithiolene complexes. Magnetic materials containing dithiolene-complex building blocks have yielded systems such as ferromagnets, ferrimagnets, metamagnets and spin ladders in addition to other model systems suitable for the study of magnetic ordering. These can involve systems where the dithiolene complex is the only paramagnetic component in addition to more complex systems involving other types of building block.     

Magnetic and electronic structure of TlCo2S2

An extensive investigation of the ferromagnetic compound TlCo₂S₂ has resulted in new information on the electronic and magnetic structure. Electronic structure calculations showed that magnetic ordering is energetically favorable with a clear driving force for ferromagnetic coupling within the cobalt layers. TlCo₂S₂ is metallic and the conductivity is due to holes in the valence band. XPS single crystal measurements did not show evidence of mixed oxidation states of cobalt. Neutron powder diffraction resulted in a ferromagnetic structure with the magnetic moment in the ab-plane. The derived magnetic moment of the cobalt atom is at 10 K and is in very good agreement with the value, at 10 K, inferred from the magnetic hysteresis curve.     

Sol–Gel Synthesis and Magnetic Studies of Titanium Dioxide Doped with 10% M (M=Fe,Mn and Ni)

TiO₂ nanocrystals doped with 1%, 5% and 10% Co/TiO₂ and 10% M (M=Fe, Mn and Ni) were prepared by the sol–gel technique and characterized using X-ray diffraction and SQUID. The as-prepared samples are found to be paramagnetic at room temperature, with the magnetic susceptibility following the Curie–Weiss law in the investigated range of 2–370 K. However, transformation from paramagnetism to room-temperature ferromagnetism (RTFM) for the 5% Co/TiO₂ was observed by hydrogenating the sample at 573 K while the 1% sample remained paramagnetic. As the percentage of Co was increased from 5% to 10% the Curie temperature increased from 390 K to 470 K determined via extrapolation. Transformation from paramagnetism to room-temperature ferromagnetism (RTFM) was also observed by hydrogenation of 10% Fe/TiO₂ at 573 K for 6 h. X-ray diffraction of the hydrogenated sample shows only single phase TiO₂ structure suggesting that the observed RTFM may be intrinsic but magnetic studies may suggest the possibility of Fe nanoparticles.     

Dual-controlled dithienylmaleimide switch containing ferrocene units

A novel photochromic dithienylmaleimide (TMF) appended with two ferrocene units was synthesized from 2,3-bis(5-bromo-2-methylthiophen-3-yl)fumaronitrile. Its photochromic properties, electrochemical properties and magnetism were studied. Both fluorescence emission and redox potential were reversibly changed accompanying the open and closed-ring photoisomerization of TMF with UV/vis light irradiation and electrochemical redox. TMF may be used for fluorescent switch and electrochemical switch controlled by both light and electrochemical redox.