Magnetic properties zero-field splitting

Magnetic exchange, 1,257, 267 polymetallic complexes, 1,138 Magnetic moment, 1, 259 Magnetic properties atomic systems, 1,260 cubic field systems, 1,263 free-atom states and terms, I, 260 lower symmetry, 1, 264 zero-field splitting, 1,262 Magnetic susceptibility, 1,256, 259 Magnetism... 

While the stoichiometries of the Mn SOD enzymes appear to vary, the properties of the Mn-binding site do not. This is borne out in the electronic spectra of these proteins, which display a great degree of similarity despite the diversity of sources from which they have been isolated (Table II). This type of spectrum is distinctive for manganese in the trivalent oxidation state (3). The native enzymes are EPR silent, as might be anticipated if they contained Mn solely as the trivalent ion (S = 2) (1, 6,12,18-20, 24). However, when the enzymes are denatured, the characteristic six-line pattern of Mn(II) (I = 5/2) appears. Magnetic susceptibility studies with the E. coli SOD were consistent with the presence of a monomeric Mn(III) complex with a zero-field splitting of 1 to 2 cm-1 (4). The enzymes are additionally metal specific (however, see Refs. 36 and 37) metal reconstitution studies with E. coli and B. stearothermophilus revealed a strict requirement for Mn for superoxide dismutase activity (2, 22, 23). 

The realization that measurements of the intensity of an MCD spectrum into the region where it is nonlinear in field and temperature could be analyzed to yield ground-state g values enabled the magnetic properties of individual paramagnetic centers in a multicentered me-talloprotein to be probed for the first time (iO). The detailed analysis of the temperature dependence of the MCD spectrum at magnetic field strengths that are within the linear limit enable the zero-field splitting... 

Returning now to the magnetic properties, the plot of /-T vs T (Figs. 7-8) reveals, at very low temperatures, the influence of intercluster interactions and zero-field splitting for Ni(II) ions. Due to this last effect, the system is then anisotropic, and the complete Hamiltonian must be written ... 

Unusual magnetic and electrical properties might also arise from quasi one-dimensional crystal structures of these compounds. The acceptor stacks /especially TCNQ/ may be either regular, i, e. with equally spaced molecules, or alternating when composed of diads, triads or tetrads. In the latter case some substances exhibit EPR spectrum characteristic of mobile, thermally activated triplet states /triplet excitons/, The spectrum may result from the excitation of two or more coupled TCNQ entities /6, 7/. The triplet character of the paramagnetic excitation is shown by the anisotropic two-lines EPR spectrum which results from a zero field splitting of the triplet levels being described by the spin Hamiltonian /8/j... 

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