摘要:

Recent results of magnetization, susceptibility and muon spin rotation (μSR) measurements and crystal structure determinations of the organic radicals based on α-nitronyl nitroxide are described. Temperasture variation of μpSR and a.c. susceptibility reveals that the organic radicals, which are found to exhibit ferromagnetic intermolecular interactions, undergo magnetic phase transitions at around 0.1-0.7 K. The organic radicals have not only a simply ferromagnetic ordered state but also canted spin magnetic orders. Microscopic views of the magnetically ordered states in the organic radicals are discussed by taking account of the molecular arrangements in the crystals.

ISSN:1058-725X    

DOI:10.1080/10587259508034043

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Magnetic properties and crystal structures of α-and β-2-hydro nitronyl nitroxide radicals (2-hydro-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide) were investigated. Exchange couplings in both phases were estimated from the parainagnetic susceptibility (1.8-300 K) and magnetization (up to 400 kOc) measurements. Assignment of the couplings to molecular packings has been carried out. Close spacing between the ONCNO moietics yields various magnitude of exchange couplings from 0 toca.-30 K. In α-phase crystal, short contacts between the central carbon atoms with negative spin density and the NO groups with positive spin density were observed. However, this packing is assigned to an antiferromagnetic exchange coupling,J/kB= −11 K (ℋ= −2JS1.S2). This case suggests that care must be taken when we refer to McConnell's proposal.

ISSN:1058-725X    

DOI:10.1080/10587259508034044

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

TheN-alkylpyridinium nitronyl nitroxide cations were intercalated into saponite clay (Na0.46[Si3.54Al0.46Mg3O10(OH)2]nH2O) by means of the cation exchange. Up to 70 % of the sodium ions were replaced by the organic radicals. The organic radical-saponite nanocomposites were found to show Curie paramagnetic behavior.

ISSN:1058-725X    

DOI:10.1080/10587259508034045

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

As a novel high-spin molecule, a through-bond spin-frustrated organic molecule 4,4′,4Prime;-trisdiphenylmethyleneamine (TDMA) and its anion and cation was studied by cw-ESR spectroscopy. TDMA is a spin frustrated system composed of three S=1 units coupled antiferromagnetically. This molecule was shown to have a triplet ground-state which is asymmetrical in its exchange interaction as well as its molecular conformation. The TDMA ions were generated at low temperature via successive radiolysis and photolysis of its diazo precursor. It was shown that the ground states of the anion and cation are quartet and sextet, respectively. This means that upon ionization the ground state changed from the intermediate-spin state of TDMA to the high-spin state of the ions, showing the interrelation between spin alignment and excess charge in a molecular field. On the other hand, in order to identify and discriminate the spin multiplicities of complicated spin assemblages in amorphous materials, we have developed electron spin transient nutation spectroscopy based on FT pulsed ESR and applied it to a pseudo one-dimensional high-spin polymer with effective spin S≥2.

ISSN:1058-725X    

DOI:10.1080/10587259508034046

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Intramolecular exchange interactions in bis(arylnitrene)s obey the Borden-Davidson disjointness criterion, although variations in the size of the interaction occur as functions of conformation and -X- in the structure: N-Aryl-X-Aryl-N:.

ISSN:1058-725X    

DOI:10.1080/10587259508034047

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The electronic structure of an ionized high spin molecule, m-phenylenebis(phenyl-methylene), is studied with a semi-empirical model for π and n electrons using the unrestricted Hartree-Fock (UHF) and resonating HF (Res HF) approximations. The injected hole or electron is in the π system and the calculated spin multiplicity of the ground state is the quartet, which is consistent with the experiments. In the UHF approximation, it makes a spin density wave (SDW) polaron localized around a carbene site. The Res HF approximation shows that quantum motion of the SDW polaron between the carbene sites and quantum fluctuations of its spins more stabilize the quartet state.

ISSN:1058-725X    

DOI:10.1080/10587259508034048

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The electronic and molecular structures of a two-dimensional septet-state molecule (S=3), 1,3,5-tris(p-methoxyphenylmethylene)benzene A, were investigated by single-crystal ESR spectroscopy. A was designed for a prototype core model for discotic liquid crystalline organic high-spin molecules. Tris(α-benzoyl)benzene was adopted as the host crystal and its crystallographic parameters were determined by X-ray diffraction: the space group Pi withZ=4,a=11.99 A,b=21.94 A,c=7.82 A, α=98.0°, β=90.9°, and γ=94.1°. The effect of the methoxy functional group on the fine-structure constants was found: the effect showed up in the significant reduction of the fine-structure constant D value, showing the modification of the topologically controlled robust π spin polarization. The observed finite E value is in accord with the molecular symmetry and crystal structure of the host molecule.

ISSN:1058-725X    

DOI:10.1080/10587259508034049

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The potential application of time domain EPR spectroscopy to an organic molecular spin system was examined, particularly focusing upon quantum spin transient nutation phenomena. A nitronyl nitroxide-based biradical with an excited triplet state (S=1),p-phenylenebis(α-nitronylnitroxide), was adopted as a simple model system for studying the nutation spectroscopy which enables us to discriminate between S≥1 andS=½ states. In the low temperature region below 10 K, anS=1 spin of the themally excited biradical molecule and anS=½ spin of an impurity molecule were found to coexist in the crystalline solid state ofp-phenylenebis(α-nitronylnitroxide). Field-swept echo-detected EPR spectra reproduced the cw spectra of the biradical powder. Echo-detected nutation spectra exhibited two distinct maxima of the echo intensity at the nutation frequencies expected forS=1 andS=½ spins, indicating that the biradical solid was identified to be a mixture of theS=1 andS=½ species as expected from the static susceptibility and crystal structure analysis of the biradical. The nutation method based on pulsed EPR spectroscopy was demonstrated to be complementary to conventional cw EPR and susceptibility measurements.

ISSN:1058-725X    

DOI:10.1080/10587259508034050

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A ground-state triplet diphenylmethylene derivative, 2,2′,3,3′,5,5′,6,6′- octamethyldiphenylmethylene (OMDPM) is a model for chemically stable organic high spin molecules. The electronic structure and the stability of OMDPM have been investigated by electron spin resonance, and the molecular conformation responsible for this stability has been shown by AM1 UHF MO calculations and LCAO MO calculations for zero-field splitting parameters. OMDPM was generated by photolysis of the corresponding diazo precursor in organic solvents or single crystals of the precursor at cryogenic temperatures. Based on the simulation of the fine-structure spectra from random orientation, the zero-field splitting parameters have been determined. The single-crystal experiment showed that OMDPM survived up to 250K. The AM1 UHF MO calculations and the LCAO MO calculations made clear the reason of this stability. Both calculations indicated that the phenyl rings of OMDPM were perpendicular to each other and that the reactive center was protected by the eight methyl groups.

ISSN:1058-725X    

DOI:10.1080/10587259508034051

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Recently, organic high-spin polymers and clusters have been emerging. With the increasing effective molecular spin quantum number S and molecular weight of the polymers, however, cw ESR spectroscopy manifests its inherent disadvantages in discriminating high spins from S=½ and in determining the S's for the complex mixture of various spin assemblages. An electron spin transient nutation method based on pulsed ESR spectroscopy has been for the first time applied to a quasi 1D high-spin polymer as one of the most complex amorphous spin assemblages, identifying that the polymer is comprised of high-spin assemblages with the S's greater than two. It can be concluded that electron spin transient nutation spectroscopy is a facile and useful method for the exclusive identification of S and ESR transitions even for the cases of apparently vanishing fine-structure splittings and for spin systems with residual fine-structure terms in the spin Hamiltonian. Fundamental bases for the transient nutation method are described, emphasizing inherent advantages in the nutation spectroscopy from the methodological viewpoint. The salient features of multiple-quantum nutations have been disclosed in this work.

ISSN:1058-725X    

DOI:10.1080/10587259508034052

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor