Diamagnetic substitution

Defects in ferrimagnetic structures often lead to noncollinear (canted) spin structures. For example, a diamagnetic substitution or a cation vacancy can result in magnetic frustration which leads to spin-canting such that a spin may form an angle 6c with the collinear spins in the sample [80, 81]. Similarly, the reduced number of neighbor ions at the surface can also lead to spin-canting [80-83]. 

Figure 6.18 shows spectra of the diamagnetically substituted ferrite, Mno.25Zno.75Fe204 [84]. The spectra were obtained in a magnetic field of 6 T... 

Most of the studies of the reactivity of this oxidation state have been carried out with these types of complexes. The low spin d Ni(IV) resembles Co(III) in being diamagnetic, substitution inert and capable of resolution into optical isomers. Reductions are outer-sphere when Co(edta), ascorbate and Co(phen)3+ Ref. 269 are used, intermediate Ni(III) species are detected and characterized. Oxidation of Co(edta) by Ni (S-Me2L) + or Ni (S-MejL), L = 12, R = R]=CH3i R2 = H, produces a =10% excess of (+)-... 

A calculation of the dipolar contribution to the magnetic anisotropy suggested that the diamagnetic substitution method was at least of qualitative value but probably cannot be trusted to provide quantitative values in highly anisotropic systems. 

Isomorphous A1 for Fe substitution in hematite is also a common phenomenon and has been intensively smdied [92,96,98-101]. Hematite can contain more than 15 at % A1 and, similarly to goethite, this diamagnetic substitution has primarily a... 

Al substitution is commonly found in soil-related maghemite. The spectra are somewhat similar to that of Al-free maghemite, but the sextet is often accompanied by a doublet (Fig. 3.16), the contribution of which decreases at lower temperatures. This typical superparamagnetic behavior is a consequence of a combined effect of particle size and diamagnetic substitution [125, 126]. 

In addition to the electron-precise 48e hydrido cluster anion 2, the 47e-radical anion, [Fe3(CO)nl 3, is regarded as a key intermediate in reductive transformation of nitroaromatics to anilines or their carbonylated derivatives. The radical 3 is formed via a redox disproportionation reaction upon treatment of 1 with halide (Cl, Br, I ) or pseudohalide (NCO ) in THF in contrast to the reactions of the Ru and Os derivatives, which afford the diamagnetic substituted anions, [M3(CO)io(/t-X)] Treatment of iron carbonyls such as 1 with trimethylamine iV-oxidc or... 

Planar-octahedral equilibria. Dissolution of planar Ni compounds in coordinating solvents such as water or pyridine frequently leads to the formation of octahedral complexes by the coordination of 2 solvent molecules. This can, on occasions, lead to solutions in which the Ni has an intermediate value of jie indicating the presence of comparable amounts of planar and octahedral molecules varying with temperature and concentration more commonly the conversion is complete and octahedral solvates can be crystallized out. Well-known examples of this behaviour are provided by the complexes [Ni(L-L)2X2] (L-L = substituted ethylenediamine, X = variety of anions) generally known by the name of their discoverer I. Lifschitz. Some of these Lifschitz salts are yellow, diamagnetic and planar, [Ni(L-L)2]X2, others are blue, paramagnetic, and octahedral, [Ni(L-L)2X2] or... 

In the following sections, systems with various numbers of electrons are discussed. When we look for aromaticity we look for (1) the presence of a diamagnetic ring current (2) equal or approximately equal bond distances, except when the symmetry of the system is disturbed by a hetero atom or in some other way (3) planarity (4) chemical stability (5) the ability to undergo aromatic substitution. 

Iron(II) complexes are often included in studies when complexes are prepared from a large number of different metal ions. 2-formylpyridine thiosemicarbazone, 5, forms brown [Fe(5)2A2] (A = Cl, Br) when prepared in ethanol and [Fe(5-H)2] from aqueous alcohol solution [156], All of these complexes are diamagnetic. The resonance Raman and infrared spectra of [Fe(5-H)2] were examined in detail [130] and coordination occurs via the pyridyl nitrogen, azomethine nitrogen and thiol sulfur. There is appreciable d-d sulfur-to-iron(II) Jt-bonding. Solution studies of iron(II) complexes of some 5-substituted-2-formylpyridine thiosemicarbazones have been reported [157], but no solids... 

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