摘要:

The approach to the design of molecular magnets based on metal complexes with 3-imidazoline nitroxides is discussed. Both polymeric bischelate complexes demonstrating bulk magnetization and molecular model compounds are considered. Some aspects of quantum-chemical treatment of exchange interactions in metal-nitroxide exchange clusters are presented.

ISSN:1058-725X    

DOI:10.1080/10587259508031845

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

New nitronyl-nitroxide biradicals based on 2,2′-bipyridine, 1,10-phenanthroline, 1,8-naphtyridine and 3,6-di-(2-pyridyl)-pyridazine have been synthezised and characterized. Aldehyde + hydroxylamine condensation in the presence of a catalytic amount of SeO2afforded, after oxidation a selective way to prepare the corresponding imino-nitroxide biradicals. Two bipyridine nitronyl-nitroxide biradicals (substituted in the 6,6′ and 5,5′ positions) have been characterized by a crystal structure determination. The 6,6′-substituted-2,2′-bipyridine and the 1,10-phenanthroline biradicals formed mononuclear Cu(II) and Ni(II) complexes which coordinate the two radicals to the central metal and display strong antiferromagnetic coupling at low temperature. The X-ray structures of the copper and nickel -2,2′-bipyridine-6,6′-biradical has also been determined.

ISSN:1058-725X    

DOI:10.1080/10587259508031846

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We analysed the temperature and field dependence of the magnetisation of the electron transfer salts meso-(Tetratolylporphinato)manganese(III)-tetracyanoethenide, [MnIIITTP]::+[TCNE]−and meso-(Tetratolylporphinato)manganese(III)-7,7,8,8-tetracyano-p-quinodimethane [MnIIITTP]::+[TCNQ]−. They show cooperative magnetic behaviour for temperatures below 10 K.

ISSN:1058-725X    

DOI:10.1080/10587259508031847

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Polymers containing tetraphenylporphyrin moieties in their side chains were prepared by radical polymerizations of 5-(4-acryloyloxyphenyl)- 10,15,20-triphenylporphine(AOTPP),5-(4-methacryloyloxyphenyl)-10,15,20- triphenylporphine(MAOTPP), 5-(4-acrylamidephenyl)-10,15,20- triphenylporphyrin (AATPP), 5-(4-methacrylamidephenyl)-10,15,20- triphenylporphyrin(MAATPP),5-(4-vinylphenyl)-10, 15, 20- triphenylporphyrin(VTPP), and by polymerizations of 5-(4-ethynylphenyl)- 10,15,20-triphenyl porphyrin (ETPP) with rhodium catalyst ((bicyclo[2,2,1]hepta-2,5-diene)rhodium (I) dimer). The magnetic behavior of their silver (II) complexes was investigated by measuring their magnetic susceptibilities and ESR spectroscopy. Comparison of their magnetic susceptibilities shows that stronger antiferromagnetic interaction was observed in polymers with carbonyl group, and that the origin of the antiferromagnetic interaction is likely due to superexchange interaction through oxygen atoms of carbonyl group.

ISSN:1058-725X    

DOI:10.1080/10587259508031848

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We report in this paper the preparation and magnetic properties of layered metal(II) hydroxynitrates and hydroxyacetates which display, according to the metal ion, either ferro (Co(II) and Ni(II)) or antiferromagnetic (Cu(II)) intralayer interactions. These compounds are shown to be suitable host lattices for organic species. 2,6- and 2,5- pyridine-based nitronyl-nitroxide biradicals have been synthesized and their magnetic properties investigated. They respectively display ferro- and antiferromagnetic behaviors. X-rays studies show an angle of 88° (in the 2,6 case) and 0° (in the 2,5 case) between both radicals. The synthesis of a new imino-nitroxide benzoic acid radical, characterized by classical methods and X-rays diffraction, and preliminary results of exchange reaction with copper(II) basic salts are also discussed.

ISSN:1058-725X    

DOI:10.1080/10587259508031849

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Hexacyanometalates [BIII(CN)6)]3- react with Lewis acids [AL]2+or A2+to give either oligonuclear complexes with high-spin ground states [BIII(CN-AIIL)6)]9+or three-dimensional (3D) networks with variable Curie temperature TC. We report the magnetic properties of (i) an heptanuclenr complex [Cr(CN-Ni(tetren)6](ClO4)9(tetren is tetraethylenepentamine) exhibiting a S = 15/2 ground state and (ii)a series of hexacyanometalates-based magnets, with TCranging from 9K to room temperature. We present the magnetic dichroic properties of some of the 3D materials, in the visible and in the X-ray range.

ISSN:1058-725X    

DOI:10.1080/10587259508031850

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The properties of magnetic solids constructed from cyanometalate building blocks are reviewed. Most of these solids adopt face-centered cubic lattices in which adjacent metal centers are linked by CN bridges; they are analogues of the long-known inorganic coordination polymer Prussian blue. Ferromagnets, ferrimagnets, and metamagnets can be obtained depending on the building blocks used. The effects of linkage disorder, site vacancies, and the inclusion of metal ions with orbitally degenerate ground states on the magnetic ordering temperature and hysteretic behavior are discussed. Substitution of lowvalent early transition metals such as vanadium(II) into the lattice leads to remarkably high magnetic ordering temperatures, in some cases above 200 K. The large exchange couplings in these vanadium-based molecular magnets are attributed to strong π-backbonding interactions with the cyanide π* orbitals.

ISSN:1058-725X    

DOI:10.1080/10587259508031851

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A strategy for the design of molecule-based magnets consists of assembling transition-metal ions in two-dimensional (2D) or three-dimensional (3D) networks in order to maximize the interactions between the magnetic centers. While increasing the dimensionality of the compounds, an increase in Tc, the critical temperature of spontaneous magnetization should, in principal, be favoured.

ISSN:1058-725X    

DOI:10.1080/10587259508031852

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

An X-ray study of a single crystal of the NBu4[MnCr(C2O4)3composition reveals a layered structure with an ordered arrangement of Mn2+and Cr3+ions. According to the data of the orientation dependence of magnetization at 4.5 K, the magnetic easy axis is aligned along the crystalc-axis. Mössbauer data analysis of isostructural NBu4[FeCr(C2O4)3] powdered material gives, on the contrary, the evidence of strong confinement of Fe2+spins to the crystal basal plane. The ferromagnetic system which arises here is a quasi-2D system in terms of the nature of its exchange interactions.

ISSN:1058-725X    

DOI:10.1080/10587259508031853

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A combination of a.c. susceptometry and Fe57Mossbauer spectroscopy measurements confirm valence trapped 3D-ferrimagnetically ordered ground states for the title compounds save (A) that orders antiferromagnetically with a very broad maximum inX′mcentered at - 50K. Their ground state magnetic behavior is contrasted with the previously demonstrated ferromagnetism of Bu4N{FeIICrIII(ox3} and φ4P{MnIICrIII(ox3)}.

ISSN:1058-725X    

DOI:10.1080/10587259508031854

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor