Spin localization

The corresponding hydrocarbon species with the same spacer length, the dianthrylundecane [6e], forms a radical anion that always exists as a spin-localized species. The esr spectrum obtained for the radical anion of the structurally related ether [7a] (see Fig. 8) is temperature-dependent, which... 

Computer simulation of the experimental spectra in the frozen solution points to a spin-localized structure independent of the temperature. This interpretation is unambiguous because, in the solid state, the dipolar contributions of the hyperfine interaction A(dip) for all three principal... 

In the radical anions of the di(2-anthryl) system [9] and of the ort/io-cyclophane [13] a spin-localized situation prevails independently of temperature and ion pairing. On the other hand, for the corresponding di(9-anthryl) species and even for the di(l-anthryl) species a rapid hopping process can be detected if suitable ion pairing is established (Becker et al., 1991). Thus, according to both cyclic voltammetric and esr spectroscopic... 

The magnetic moments of the Ni clusters are dominated by the contribution from surface atoms.48,69 The analysis of Wan et al. indicates that the orbital and spin local moments of cluster atoms with atomic coordination 8 or larger are similar to those in the bulk (p spin 0.55 and orb 0.05 pB) 73 that is, the orbital moment is almost quenched for internal cluster atoms. In contrast, there is a large enhancement of the spin and orbital moments for atoms with coordination less than 8. This enhancement increases with the coordination deficit, and it is larger for the orbital moment. Wan et al.48 also analyzed the quantum confinement effect proposed by Fujima and Yamaguchi,56 i.e., the... 

Fig. 4 Stacked Fourier transforms of the NMR spin echoes in D-RADP-25 versus echo delay time at T = 65 K. In contrast to D-RADP-20 (Fig. 2) there are still two rims present at this low temperature indicating the coexistence of two different phase states. The rim at the Larmor frequency vl originates from Rb spins localized in short range ordered glass clusters, whereas the rim at vl + 8 kHz is produced by spins sitting in FE clusters [17]...

The formation of oxidation products a-c in a range of G values (0.7-3.8) during the 7-R of S in 02-saturated DCE suggests that a-c would be produced from complicated reactions of peroxy radicals with S (Table 5). On the other hand, the regioselective formation of 3d with large G values (2.6-3.0) in oxidation of 3 with O2 is explained by spin localization on the p-olefinic carbon because of the contribution of (B) in 3. The results of products analyses are essentially identical with prediction based on k and ko for S measured with PR. It should be emphasized that the reactivities of c-t unimolecular isomerization and reaction of S with O2 can be understood in terms of charge-spin separation induced by p-MeO. 

Remarkable enhancements of the unimolecular c-t isomerization of c-S with p-MeO and oxidation of S with -MeO are explained by charge-spin separation in such S Unimolecular c-t isomerization of such c-S proceeds with a chain mechanism, while regioselective oxidation occurs in such S because of the spin localization. Cycloreversion of t,c,t-TPCB occurs to give a a-St 2, while the photochemical cycloreversion of TPCB and t,t,t-TPCB gives Tr-St 2 and t-St /t-St pair, respectively. Radical cations of phosphorus compounds (9 and 10 form intramolecular rr-dimer between two Nps from which Np 2 forms. Formation of intermolecular a-dimer of aromatic acetylene (11 - and 12 -) and intramolecular dimer of 13 and diarylmethanoT was observed, and the n = 3 rule is not effective for intramolecular dimer -. 

In the same paper, Brooks and Kelly have considered the possible contributions of 5 f orbitals to the bonding of UO2. While the hypothesis of an itinerant picture for these orbitals in the solids leads to a 35% higher atomic volume than the observed one, the assumption of a 5 f Mott-Hubbard spin-localized band, comprising seven states per atom (instead of 14) (see Chap. A) yields the correct value for this quantity. A certain amount of f-p hybridization is found as a weak and diffuse percentage of 5 f character in the predominantly 2p-6d valence band of this oxide. 

Ortho substituents can influence the rate of cyclization to azirines by both steric and electronic (spin localization) effects. Sundberg et alf demonstrated that the steric effect is dominant with simple alkyl substituents. 

A single ortho- (8a) or para- (8b) methyl substituent has no influence on the rate of cyclization of the singlet tolylnitrene to the azirine (Fig. 10, Table 4, Scheme 3). Spin localization effects are not observed as with cyano and phenyl substitution. Cyclization of 2,6-dimethylphenyl or 2,4,6-trimethylphenylnitrenes necessarily proceeds towards a carbon bearing a substituent. The steric effect raises the barrier to cyclization by 1.5-2.0kcal/mol, in excellent agreement with the predictions of Karney and Borden. The steric effect extends the lifetime of 2,6-dimethylphenylnitrene at ambient temperature to 13 ns in freon-113 and of 2,4,6-trimethylphenylnitrene to 8 ns, in the same solvent. 

Product studies (Table 5) demonstrate that 2-cyanophenylnitrene (8c) prefers to cyclize towards the cyano group in pentane solvent. Thus, the spin localization effect and steric effect essentially cancel and there is no... 

In molecules, the interaction of surrogate spins localized at the atomic centers is calculated describing a picture of spin-spin interaction of atoms. This picture became prominent for the description of the magnetic behavior of transition-metal clusters, where the coupling type (parallel or antiparallel) of surrogate spins localized at the metal centers is of interest. Once such a description is available it is possible to analyze any wave function with respect to the coupling type between the metal centers. Then, local spin operators can be employed in the Heisenberg Spin Hamiltonian. An overview over wave-function analyses for open-shell molecules with respect to local spins can be found in Ref. (118). 

The porphyrin-cobalt complex gives rise to the cation radical with charge spin localization at the nitrogen atom of the porphyrin ring. The cation radical thus formed acquires enhanced reactivity and can add tolane (Kochi 1986), Scheme 1-52. The main point... 

When the magnitudes of the dipolar hyperfine interactions in the dimers are compared with a theoretical value of 67.5 G for an unpaired spin localized in a Ni 3d orbital (87), it can be seen that the molecular orbital containing the unpaired spin has a relatively small contribution from Ni (<30%). A similar situation is observed in H2ases. When bacteria are raised on a source of 61Ni, hyperfine is observed in the EPR signal originating from H2ase (22). (In fact, observation of this hyperfine was... 

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