摘要:

This paper deals with a polymer version of the topological π-spin polarization interrelated to the topological superdegeneracy of crystal orbitals of infinite or extended polymeric spin systems and also with a VB picture of their spin structure in terms of simple electronic band calculations. We stress that the theoretical models (traveling wave approach) introduced predict essential features of magnetic properties of polymeric systems which yield crucial aspects for their materials design. The model calculation has also been made for various types of inter-polymer interactions in order to understand the topological spin polarization of higher-dimensional infinite or extended polymeric spin systems and the topological nature of inter-polymer contacts (inter-polymer connectedness). The results have shown that the connectedness gives rise to the prominent modulation of band structures and π spin polarizations which is highly dependent on the topology of the contacts. Thus, the results serve for molecular designs for novel intriguing organic magnetic systems such as multifunctionality molecular magnetic materials. The VB representation in the k space has disclosed such a physical picture for the infinite spin system that can not be expected from the simple or intuitive extension obtained for a finite system. Naturally, in the VB picture the contributing weight of a particular spin structure undergoes fluctuation in the k space as the physical consequence of the intersegment interaction in the infinite system.

ISSN:1058-725X    

DOI:10.1080/10587259508055269

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The magnetic behavior of stable free radical crystals ofN-(arylthio)-2,4,6-triarylphenylaminyl are described as studied by the magnetic susceptibility and ESR measurements. The temperature dependence of the magnetic susceptibility and the ESR spectrum were examined from 1.7 K to room temperature. When the temperature is decreased from 298 to 2 K, the line width of the ESR spectrum increases enormously below 5 K in the case ofN-[(2,4-dichlorophenyl)thio]-2,4,6-tris(3-chlorophenyl)phenylaminyl radical crystals, 1. The susceptibility measurements of 1 show the intermolecular ferromagnetic (FM) interaction among the radical spins. The productXmolTincreases with lowering of the temperature. The Weiss constant, Θ, obtained for the Curie-Weiss law, is +5.7 K, indicating ferromagnetic intermolecular interaction among the spins. The magnitude of the FM interaction is fairly large, compared with those of other purely organic ferromagnets.

ISSN:1058-725X    

DOI:10.1080/10587259508055270

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper deals with intramolecular spin alignment in organic high-spin molecules and focus especially on a large negative spin polarization induced by π-topology. Utilizing a topological connectivity of π-electron network, spin inverted moiety with large negative spin densities can be realized in organic high-spin molecules, which are models of polymer-based ferrimagnets. As an example, two different organic high-spin molecules, 3,4′-diphenylmethylenbis(phenylmethylene) and 4-(diphenylmethylene)-4′-(m- phenylenbis(phenylmethylene))-ether, have been investigated. In order to clarify the electronic structure, the spin density distributions have been determined by single-crystal ESR and ENDOR experiments. The analysis of the1H- and13C-hyperfine tensors gives a clear evidence of the large negative spin polarization. The spin alignment in these molecules is discussed in terms of the VB picture based on a generalized Hubbard model.

ISSN:1058-725X    

DOI:10.1080/10587259508055271

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In order to clarify the spin dynamics of the stable radical crystals, we have investigated the magnetic behavior and spin relaxation of low-dimensional antiferromagnetic organic materials,N-[(3-Nitropheny])thio]-2,4,6-triphenylphenylaminyl radical crystals, by cw and pulsed ESR. With decreasing temperature from 298 to 20 K, the line width of the cw ESR spectrum increases. Upon further decrease of temperature, significant exchange narrowing occurs below 10 K. The line broadening is more prominent in the direction ofg// than that ofg1. The temperature dependence of the inverse of the transverse relaxation time,T2, for theg// direction shows a divergence at ca. 20 K as determined by the FID analysis. This temperature is consistent with the magnitude of an antiferromagnetic interaction ofJ/k= -26 K. These findings indicate that the spin relaxation and spin dynamics in this system are governed by low-dimensional antiferromagnetic interactions among the radical species.

ISSN:1058-725X    

DOI:10.1080/10587259508055272

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

C60[TDAE] was the first and so far the only C60CT complex which ex-hibits molecular ferromagnetism with a Curie temperature of about 16 K [1]. Despite extensively investigated a convincing access to the origin of the low temperature phase of this C60CT complex is still missing. The 3 fold degeneracy of the C60HOMO is lifted by a change of the C60conformation, and we find a transition from a static low temperature Jahn-Teller distortion to a dynamic one at about 140 K. The excess electron is concentrated in a belt around the equator of the C60-. The distorted C60molecules have a spin density distribution with an axial symmetry and are aligned along the crystallographic axes. This orientational ordering of the C60- molecules is the necessary precursor to a ferromagnetic spin glass type ordering in C60[TDAE] which was interpreted in terms of spin polarisation between C60- and TDAE+*by Yamaguchi et a1 [2].

ISSN:1058-725X    

DOI:10.1080/10587259508055273

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The synthesis and solution phase EPR spectrum of a new biradical is presented. The H-hyperfine coupling constants of the biradical indicate interaction of the unpaired electrons in the molecule.

ISSN:1058-725X    

DOI:10.1080/10587259508055274

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Organic poly radical ions are molecular spin units which could be used in the construction of magnetic materials. They possess the feature of redox activation / deactivation, a potential means of reversibly controlling the molecular spin state of the unit, thus imparting a magnetic switch function. Here, we describe the prospect of preparing tris arylamines suitably structured to yield long-lived cation, dication, and trication states of successively higher spin mutiplicity. The preparation and oxidation of N,N,N′,N′,N″,N″-hexa-p-anisyl-1,3,5-triaminobenzene (HATAB) are discussed, along with the ESR spectra of the HATAB higher oxidation states. The HATAB2+and HATAB3+ESR signals are assigned to triplet and quartet states respectively which, on the basis of cursory Curie-Weiss data, are tentatively assigned as the ground states of these poly cations, consistent with calculational results (AMI/UHF)on the unsubstituted system, 1,3,5-triaminobenzene dication and trication.

ISSN:1058-725X    

DOI:10.1080/10587259508055275

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A series of new heterocyclic stable free radicals based on the thioaminyl fragment1was designed in order to introduce ax-delocalized spin to the rigid cores of mesogenic molecules. The design allows for preparation of calamitic and discotic liquid crystals. Computational analysis and first experimental results of the radicals (ESR) are presented.

ISSN:1058-725X    

DOI:10.1080/10587259508055276

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A phenyl diethynyl bridge is used as a magnetic coupling unit (MCU) between two iminonitroxide π-radicals. The ethynyl moiety is attached to the central phenyl ring either in the para or in the meta position. The magnetic properties of the resulting bis-imino nitroxide diradicals (p-BIN andm-BIN) are investigated both at the molecular scale and in the condensed phases. An intramolecular through bond spin coupling is observed at an unusual long distance (about 20 ÅS) in both derivatives. However, the ground state is found to be a singlet spin state in both compounds. The results suggest an interplay between the spin polarization and the spin delocalization (π-conjugation). An intermolecular weak antiferromagnetic spin coupling is occuring in both compounds.

ISSN:1058-725X    

DOI:10.1080/10587259508055277

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Orthogonal alignment and variation of the MO-coefficients at the bridgehead postion has been tested for high spin formation in directly linked arylenes. In 2,21-bipyrenyl and para-terpyrenyl possessing very small MO-coefficients but also small steric indrance bi- and triradicalanionss are found to be in low spin groundstate, with thermally excited triplet and quartet states 100-1000 calmol−1higher in energy, respectively. For 9,91-bianthryl biradical formation is well established, such that higher oligomers have been charged resulting in a S = 3/2 for the trimer, a S = 2 for the tetramer and a polyanionradical with descrete S = 1, S = 3/2, and S = 2 states in the polymer, where this highly charged material becomes insoluble. The ground state is again low spin due to increased deviation from orthogonality at low temperatures. The thermally activated higher spin multiplicities are found with AEST= 60 cal/mol (S=1), AEDQua= 120 Cal/mol (S=3/2), and AESQuin= 180 cal/mol (s=2).

ISSN:1058-725X    

DOI:10.1080/10587259508055278

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor