Contrast paramagnetic

D. M., Hsiao, J.K., Chang, C. et al. (2008) High-contrast paramagnetic fluorescent mesoporous silica nanorods as a multifunctional cell-imaging probe. 

NMR is an important teclnhque for the study of flow and diflfiision, since the measurement may be made highly sensitive to motion without in any way influencing the motion under study. In analogy to many non-NMR-methods, mass transport can be visualized by imaging the distribution of magnetic tracers as a fiinction of time. Tracers may include paramagnetic contrast agents which, in particular, reduce the transverse... 

The negative sign in equation (b 1.15.26) implies that, unlike the case for electron spins, states with larger magnetic quantum number have smaller energy for g O. In contrast to the g-value in EPR experiments, g is an inlierent property of the nucleus. NMR resonances are not easily detected in paramagnetic systems because of sensitivity problems and increased linewidths caused by the presence of unpaired electron spins. 

Compounds containing M-C cr-bonds are frequently unstable and do not give rise to an extensive chemistry (p. 999). Vanadium forms a neutral (paramagnetic) hexacarbonyl which, though not very stable, contrasts with that of titanium in that it can at least be prepared in... 

In contrast, Skell and co-workers 169) demonstrated that there could be prepared, by the metal atom method, a reasonably well-defined, paramagnetic, yellow TijCCgHgls compound which, in THF, is rapidly reduced with potassium to yield a fairly stable, green solution of the diamagnetic dianion. The H-NMR spectrum and the analytical data were all consistent with the formulation of the green dianion shown, which appears to be the... 

The electronic absorption spectra of the products of one-electron electrochemical reduction of the iron(III) phenyl porphyrin complexes have characteristics of both iron(II) porphyrin and iron(III) porphyrin radical anion species, and an electronic structure involving both re.sonance forms Fe"(Por)Ph] and tFe "(Por—)Ph has been propo.sed. Chemical reduction of Fe(TPP)R to the iron(II) anion Fe(TPP)R) (R = Et or /7-Pr) was achieved using Li BHEt3 or K(BH(i-Bu)3 as the reductant in benzene/THF solution at room temperature in the dark. The resonances of the -propyl group in the F NMR spectrum of Fe(TPP)(rt-Pr) appear in the upfield positions (—0.5 to —6.0 ppm) expected for a diamagnetic porphyrin complex. This contrasts with the paramagnetic, 5 = 2 spin state observed... 

In contrast to chloride compounds, niobium oxides have a VEC of 14 electrons, due to an overall anti-bonding character of the a2u state, caused by a stronger Nb-O anti-bonding contribution. In some cases, the VEC cannot be determined unambiguously due to the uncertainty in the electron distribution between the clusters and additional niobium atoms present in the majority of the structures. The 14-electron compounds exhibit semiconducting properties and weak temperature-independent paramagnetism. Unlike niobium chlorides, the oxides do not exhibit a correlation between the electronic configuration and intra-cluster bond distances. 

In contrast to 4, 2-acetylpyridine iV-methylthiosemicarbazone, 3a, formed yellow-green, paramagnetic, octahedral [Ni(3a)2A2] complexes with nickel(II) chloride and bromide. The neutral form of the ligand was proposed to be NN eoordinated [180]. Brown, paramagnetic [Ni(3a-H)2] was prepared from nickel(II) acetate with NNS coordination, and its d-d spectrum and ligand field... 

The W(IV) compounds W(Et2C c)4 (14) and [(CU.2)ndtc] (15) are characterised only by analytical data and magnetic susceptibility measurements. They are considered to be paramagnetic with moments of about 1.0 BM, which is in contrast with the diamagnetism of W(R2[Pg.94]

In contrast, soft magnetic solids and paramagnetic systems with weak anisotropy may be completely polarized by an applied field, that is, the effective field at the Mossbauer nucleus is along the direction of the applied field, whereas the EFG is powder-distributed as in the case of crystallites or molecules. In this case, first-order quadrupole shifts cannot be observed in the magnetic Mossbauer spectra because they are symmetrically smeared out around the unperturbed positions of hyperfine fines, as given by the powder average of EQ mj, d, in (4.51). The result is a symmetric broadening of all hyperfine fines (however, distinct asymmetries arise if the first-order condition is violated). 

The trace of D vanishes when dipole coupling between paramagnetic centers determines the ZFS, since dipole interaction is traceless. A typical example is the ZFS of triplets arising from coupled radical pairs, for which SOC is negligible. For transition metal ions in contrast, SOC is the leading contribution to ZFS and the trace of Zl in general has finite values. 

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