Polynuclear manganese grids and clusters—A magnetic perspective

High nuclearity paramagnetic, spin-coupled transition metal clusters and grids are fascinating chemists and physicists partly because of their structural beauty, and the challenge of creating them, but also because of their novel physical properties. Magnetic interactions between the spin centers are a primary focus. This review will examine a selection of Mn(II) polynuclear grids and clusters, with nuclearities in the range Mn₄ to Mn₉. Theoretical treatments of the magnetic properties are discussed, and approaches to solving the exchange problem for ‘large’ spin systems related to computational difficulties. A freely available software package (MAGMUN4.1) is presented as a means of dealing simply with spin-coupled clusters in general, and symmetry reduction methods are discussed briefly as a means of dealing with ‘large’ spin systems.     

顺磁性聚酯金属配合物的合成及其驰豫性能的研究

本文通过二乙三胺五乙酸（ＤＴＰＡ）或乙二胺四乙酸（ＥＤＴＡ）的双酸酐与二元醇或二元酚进行聚合反应，制备了两个系列共１５种新的聚酯型大分子配体及其顺磁性金属配合物，用核磁、红外光谱以及元素分析表征了配体和配合物的结构。初步试验结果表明，与相应的小分子金属配合物相比，聚酯金属配合物具有较高的弛豫性能。     

THE EFEFCT OF MAGNETIC FIELD ON POLYMERIZATION OF STYRENE IN THE PRESENCE OF POLYVINYL NAPHTHALENE AND POLYVINYL BENZOPHENONE

In the process of bulk photopolymerization of styrene initiated by AIBN decomposition polyvinyl benzophenone (PVB) can supply an effective cage for triplet-triplet energy transfer between PVB macromolecules and small molecules of AIBN to influence the molecular weight of polystyrene in weak magnetic field (less than 0.035T), that was different from the case of polyvinyl naphthalene (PVN) which supplied cages for this system only in the stronger magnetic field (more than 0.2 T) studies. It was found that in the same conditions, PVN could exert more tremendous influences on the bulk photopolymerizatiou system of styrene than PVB because in the stronger magnetic field the triplet PVN had much longer life time than PVB.     

Synthesis,Characterization and Magnetic Properties of New Dinuclear Copper(II) Complexes with N,N′‐Disubstituted Dithiooxamides derived from α‐Amino Acids

Four new dinuclear copper(II) complexes have been synthesized and have the general formula [Cu₂(L)(H₂O)₂], where L = GLYDTO [N,N′‐bis(carboxymethyl)dithiooxamide], ALADTO [N,N′‐bis(carboxyethyl)dithiooxamide], VALDTO [N,N′‐bis(1‐carboxy‐2‐methylpropyl)dithiooxamide] and LEUDTO [N,N′‐bis(1‐carboxy‐3‐methylbutyl)dithiooxamide]. The complexes were characterized by elemental analysis as well as by IR, electronic and EPR spectroscopy. These techniques provided evidence for the presence of the CuNO₂S chromophore. Magnetic susceptibility measurements on all the complexes in the range 4–300 K show the existence of a dominant antiferromagnetic interaction with ?J values greater than 300 cm^?1. Thermal decomposition behaviour of the complexes was studied by thermogravimetry.     

利用DPN技术直接构建磁性纳米图形

在纳米尺度下构建有序的磁性模板和图形是当前的研究热点之一 [1,2 ] .这种模板在生物样品的分离[1] 、磁电子学研究和信息存储 [2 ] 等领域具有重要意义 .目前 ,光刻 [3] 、微触点印刷 [4 ] 和自组装 [5] 等多项技术已被用来构建各种纳米模板 .1 999年 ,美国西北大学 Mirkin小组 [6 ]发明的 Dip- pen纳米刻蚀技术 (简称 DPN技术 )更在可控组装方面显示出巨大优越性 .这项技术是在一定驱动力作用下 ,使吸附在原子力显微镜 ( AFM)针尖上的分子“墨水”逐渐转移到基底表面上 ,实现纳米模板的可控构建 .与传统技术相比 ,DPN技术可在纳米尺…     

Non empirical quantum mechanical calculations of the1H,13C,15N and17O magnetic shielding constants and of the spin-spin coupling constants in formamide,hydrated formamide and N-methylformamide

The magnetic shielding constants of the different atoms of formamide, hydrated formamide and N-methylformamide are calculated by anab initio method. For the protons of formamide the measured differences between their chemical shifts are correctly reproduced by theory, provided that the molecular geometry used as input is carefully chosen. The differences between the values of the magnetic shielding constants calculated for formamide and hydrated formamide show that intermolecular hydrogen bonding produces variations of chemical shifts for all the atoms of the molecule except the formyl proton. The calculated chemical shift variations between formamide and N-methylformamide are compared to the experimental values and discussed in relation with different hydrogen bonding possibilities of the two molecules. The calculation of the contact term of the spin-spin coupling constants of formamide and hydrated formamide shows that in most cases the measured trends are satisfactorily reproduced and that the variations of these terms upon hydration are less than 3%.     

Magnetic Orbitals and Mechanisms of Exchange I. Direct Exchange

Summary. The problem of direct exchange is examined in the simplest cases (formal coupling of two electrons initially isolated and hydrogen molecule). Then we consider the general case of a solid characterized by weak overlaps between the atomic orbitals of first-nearest neighbours so that the involved electrons are quasi-localized. We recall the physical origin of spin-orbit coupling. Its influence on direct exchange allows one to revisit Hunds rules and to express phenomenological Hamiltonians describing anisotropic couplings as well as the antisymmetrical Dzialoshinski-Moriya coupling.     

Transition metal complexes with thiosemicarbazide-based ligands,IV: Synthesis and molecular structure of 5-nitrosalicylaldehyde S-methylisothiosemicarbazonato-piperidine-copper(II)

Summary The reaction of warmDMF solutions of Cu(II) perchlorate, 5-nitrosalicylaldehyde S-methylisothiosemicarbazone (H₂ L) and piperidine (Pip) yielded the paramagnetic (_eff=2.19 B.M.) Cu(L)Pip complex, whereL is the dianionic form of H₂ L, formed as a result of deprotonation of the phenolic hydroxyl and NH₂ group. Crystal data of the complex are: monoclinic P2₁,a=11.902(4),b=6.765(3),c=11.343(4)Å; =112.92°,V=841.20(8)ų,M=400.9,Z=2,d ₀=1.60 gcm^–3,d _c =1.58 gcm^–3,F(000)=424. The structure was refined to a residualR=0.047. The copper(II) ion is coordinated in a square-planar arrangement by the piperidine nitrogen and the NNO set of donor atoms ofL.

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Komplexe der Übergangsmetalle mit Thiosemicarbazid-Liganden, IV. Synthese und molekulare Struktur von 5-Nitrosalicylaldehyd-S-methylisothiosemicarbazonato-piperidin-kupfer(II)

Zusammenfassung Durch die Reaktion in warmenDMF-Lösungen von Cu(II) Perchlorat, 5-Nitrosalicylaldehyd-S-methylisothiosemicarbazon (H₂ L) und Piperidin (Pip) wurde ein paramagnetischer Komplex (_eff=2.19 B.M.) Cu(L)Pip erhalten, wobeiL nach doppelter Deprotonierung (NH₂- und Phenolhydroxyl-Gruppe) als dianionische Form von H₂ L vorliegt. Die kristallographischen Daten des Komplexes sind: monokline Raumgruppe P2₁,a=11.902(4),b=6.765(3),c=11.343(4)Å, =112.92°;V=841.20ų,M=400.9,Z=2,d ₀=1.60 gcm^–3,d _c =1.58 gcm^–3,F(000)=424. Die struktur wurde bis zu einemR-Wert von 0.047 verfeinert. Die Koordination des Kupfers wird quadratisch-planar über den Piperidin-Stickstoff und die NNO-Donorhülle der Chelatliganden gebildet.

     

Electrical resistivity, optical and magnetic properties of the layered oxyselenide SmCuOSe

The electrical and magnetic properties of the tetragonal phase SmCuOSe are reported as a function of the temperature. The optical properties were studied by means of diffuse reflectance spectrum in the UV-Vis range. The electrical resistivity measurements as well as diffuse reflectance spectrum show that SmCuOSe is a semiconductor with an optical band gap (E_g) of 2.6 eV. In this phase, Cu is at its monovalent oxidation state and, as such, it does not contribute to the total magnetic moment, whereas Sm is in its 3+ oxidation state, with a large VanVleck contribution due to the admixture of the fundamental state with higher energy levels.     

Synthesis of magnetic DDAB vesicles

The synthesis of magnetic vesicles is described. The vesicles are constituted by didodecyldimethylammonium bromide and have a diameter of about 1 m. An aqueous magnetic fluid, constituted by charged magnetic nanoparticles dispersed in water without surfactant, is encapsulated in the vesicle with a volume fraction in particles that may range up to 10%. The first step of the encapsulation is the synthesis of a multiple emulsion the intermediate oily phase being evaporated to obtain the DDAB bilayer. The magnetic vesicles thus synthesized align and change shape when a magnetic field is applied.