摘要:

No-overlap and orientation principles for ferromagnetic interactions between organic radicals were derived on the basis of approximately spin-projected UMP4(2) and UCC SD(T)/4-31G computations for several typical radical pairs. Ferromagnetic intermolecular interactions are feasible at T-shape and rhombus conformations in parallel interplane orientations for radical pairs because of no-overlap between π*-type SOMOs (no kinetic exchange) and nonzero-potential exchange via the SOMO-SOMO through-space contact, whereas antiferromagnetic kinetic exchange interactions are predominant at many other conformations.

ISSN:1058-725X    

DOI:10.1080/10587259508055279

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The poly(phenylenevinylene) skeleton was selected as a magnetic coupler of polyradicals, because of its developed π-conjugation, coplanarity, and solvent-solubility even after substitution on the phenylene ring. By synthesizing poly(1,4- or 1,2-phenylenevinylene)-2- or -4-substituted with a stable phenoxy or nitroxy radical, an intramolecular, through-bond and long-range, but strong, ferromagnetic exchange interaction was realized for the first time. The polyradicals were chemically stable and, even at their spin concentration ofca. 0.5, displayedSvalues of 2/2 ∼ 4/2.

ISSN:1058-725X    

DOI:10.1080/10587259508055280

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Between 1978 and 1989, Mukai and coworkers demonstrated that a series of spin-labeled benzo-15-crown-5 derivatives gave triplet ESR spectra in ethanol glasses in the presence of diamagnetic alkali and alkaline earth ions. They proposed that the high-spin coupling resulted from a pair of radicals being brought into close contact by a 1:2 complexation of metal ions with the crown ether moieties. The work of Mukai and his colleagues represents an early example of high-spin coupling induced in radical pairs that assemble around diamagnetic metal ions. Herein, we describe ion binding experiments with simple stable free radicals such as TEMPO and galvinoxyl that lack the crown moiety. The triplet state species that we observe require the possibility of unforeseen mechanisms for previously reported high-spin associations in spin labeled crown ethers.

ISSN:1058-725X    

DOI:10.1080/10587259508055281

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A series of substituted alkali metal benzophenone ketyls was prepared and studied by ESR at low temperature. These species form triplet radical pairs in THF solution. Zero-field splitting parameters show that the high-spin behavior of these systems is unaffected by a variety of electronically and sterically perturbing substituents. The use of ketyl radical pairs as building blocks in the construction of molecular magnetic materials is suggested.

ISSN:1058-725X    

DOI:10.1080/10587259508055282

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Poly(phenylenevinylene)s with built-in radical groups are expected to show magnetic interaction caused by spin polarization and/or coplanarity of the π-conjugated chain. Diradical models for the poly(phenylenevinyllene)- based polyradicals were synthesized, and the magnetic properties were discussed based on ESR spectra and magnetic measurement. Magnetization and magnetic susceptibilities of the polyradicals,tert-butylnitroxyl- and 2,6-di-tert-butylphenoxyl-substituted poly(1,2- or 1,4-phenylenevinylene), indicated the occurrence of ferromagnetic interaction corresponding to these oligomeric diradicals.

ISSN:1058-725X    

DOI:10.1080/10587259508055283

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The full-potentail LAPW band calculation in paramagnetic state is carried out for hypothetical square lattices of H2NO chains by assuming two kinds of stacking of H2NO molecule: face-to-face stacking and anti-phase alternating stacking. In the former case the ferromagnetic state is never expected to be realized, but in the latter case there is a possibility of appearance of ferromagnetic phase.

ISSN:1058-725X    

DOI:10.1080/10587259508055284

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A polyfluorotriarylmethane polymer was prepared by the reaction of 3,5-diflurophenol (3,5-DFPh) with pentaflurobenzaldehyde (PFBA). The polymer obtained was characterized by NMR, FT-IR, UVVis, MS and Gel permeation Chromatography (GPC). It was found that phenolic ring in the polymer was connected at meta-position by methine carbon, and that molecular weight distribution of the polymer consists of mainly four components ranging from 6,000 to ca. 1,000,000. Further oxidation of this polymer generates the radicals which are stable in air for at least 3 months.

ISSN:1058-725X    

DOI:10.1080/10587259508055285

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A series of di-, tri-, tetra-, and pentaamines were synthesized as precursors of corresponding aminium radical-cations. Redox properties of these amines were studied by cyclic voltammetry and aminium radical-cations obtained by chemical oxidation of these amines were investigated by ESR and UV-VIS spectroscopy.

ISSN:1058-725X    

DOI:10.1080/10587259508055286

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The charge-transfer (CT) complexes of a series of 4,4,5,5-tetramethylimidazolin-1-oxyls substituted with 4-(N-alkylpyridinium) groups at the 2-position with two radical anions, tetrafluorotetracyanoquinodimethanide (TCNQF4–) and hexacyanobutadienide (HCBD–) were prepared and their magnetic properties were investigated in the temperature range of 5 to 300 K. Ferromagnetic interaction was observed for the three CT complexes. Furthermore, the magnetic measurement at lower temperatures than 5 K showed that these CT complexes exhibited a ferromagnetic phase transition between 0.4 and 0.55 K. Consequently, the present CT complexes make a group of another type of organic ferromagnets without any magnetic metal elements.

ISSN:1058-725X    

DOI:10.1080/10587259508055287

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Room-temperature molecular magnets based on V/TCNE may be prepared via two routes, identified as V(C6H6)2/TCNE/CH2Cl2and V(CO)6/TCNE/CH2Cl2. Both compounds have critical temperatures exceeding 350 K. The magnetization M(T,H) of samples prepared via both routes have been compared. The saturation magnetization of the V(CO)6-derived material (M0∼104emu·Oe·mol−1) is larger than that observed for V(C6H6)6-derived materials (M0∼ 0.6 × 104emu·Oe·mol−1), and the behavior of M(T) at H = 100 Oe is more like that exhibited by crystalline magnets. Whereas V(C6H6)2/TCNE/CH2Cl2has a linear M(T) for 5 ≈ T ≈ 300 K, the magnetization of V(CO)6/TCNE/CH2Cl2follows the Bloch spin-wave form M(T) = M(0)(1 - BT3/2), where the zero-temperature magnetization M(0) is suppressed from M0by the effect of random magnetic anisotropy (RMA). The values of M(0) and the spin-wave dispersion constant B, as well as the range of validity of the T3/2law, vary among different preparations of the magnet, reflecting a correlation between magnetic and structural anisotropies. For the V(CO)6-derived magnet, near Tc≈ 370 K, the large value of the critical exponent β = 0.6 reflects the presence of RMA, consistent with other V/TCNE systems. A scaling analysis is presented.

ISSN:1058-725X    

DOI:10.1080/10587259508055288

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor